gmw.conservation.ca.gov · •• k. I Gribaldo, Jacobs, Jones and Asso.ciates Consulting Engineers • Soil, Foundation and Geological Engineers 333 Fairchil.d Drive (P.O. Box 669),

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REVISED REPORT

to

WESTBOROUGH HOMES

South San Francisco, California

of

SOIL INVESTIGATION

for

WESTBOROUGH

South San Francisco i,. California·

by

GRIBALDO, JACOBS, JONES AND ASSOCIATES 333 Fairchild Drive

Mountain View, California

November 1964

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Gribaldo, Jacobs, Jones and Asso.ciates Consulting Engineers • Soil, Foundation and Geological Engineers 333 Fairchil.d Drive (P.O. Box 669), Mountain View. California 94042 967-6982 I 739-5823 Oakland /Watsonville

File No. E2204-Ml 5 April 1965

Westborough Homes #1 Westborough Boulevard South San Francisco, California

Subject: Westborough, South San Francisco, California. EARTHQUAKE DESIGN CRITERION.

Gentlemen:

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Further to our Revised Soil Investigation Report of 30 November 1964, it is our opinion that it would be proper and prudent to consider the numerical coefficient for base shear to be 0.16 rather than the.vaiue of o.nrpresently given in the mos& recent edition of the Uniform Building Code.

Very truly yours.,

GRIBALDO, JACOBS, JONES AND ASSOCIATES

·-~~~/J. Ph' p V. Burkland~

Wil~.{~~ C.E. 9565 f-n. PVB:WFJ:pl

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Consulting Engineers • Soil, Foundation and e:.eo1og1ca1 t:ngmeers 333 Fairchild Drive (P.O. Box 669), Mountain View, California 94042 967 -6982 I 739-5823 Oakland I Watsorwille

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File No- E2204-Ml 30 November 1964

Westborough.Homes #1 Westborough Boulevard South San Francisco, California

Subject: Westborough, South San Francisco, California. REVISED SOIL INVESTIGATION REPORT.

Gentlemen:

Transmitted herewith is a revised and updated report of the Soil Investigation for Westborough. Since the submittal of our original report entitled "Preliminary Soil Investigati.on for Callan Park Subdivision," in July 1960, we have. had occasion to make several additional field investigations and engineering studies for various purposes.

The attached report, therefore, includes not only the data and recommendations presented in the 1960 report, but also the results and recommendations culminating from subsequent investigative work.

The basic requirements and recommendations as presented in the 1960 report remain unchanged, except in those instances where the concept of development now differs from that originally contemplated _. as in the case of !!...l.9oe§...being constructed to great~r vertical Q!ights, or significantly lar~er structures being proposed,·· or where soil or ge~ CJm_ifi_tlQ!l_s tiave been revealed which require modification of any of those recommendations originally presented. We have attempted to clearly define in the Revised Report any additions to, or changes from, the data as originally presented.

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File No. E2204-Ml 30 November 1964

We trust this Revised Report will prove more useful in its application to the projects yet unfinished within the Westborough property. It is not, however, all-inclusive since the founrl.atiop recommendat!~ns are general and li:!!Q.ts!f. to one- and twQ-story frame:01ct11r;s of cgnventional gesign.""-Specific foundation design criteria must be provided aeiaratelS for any structures greater than two-s tories Ji heilCt, once their locations and.structural typer:i are known .•

Very truly yours,

ASSOCIATES

PVB:WFJ/lb

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PREFACE

Object


The objectives of this investigation were to determine

the soil and geologic conditions at the property knoWn.

as Westborough (originally referenced as Callan Park),

particularly their engineering characteristics when

subjected to large-scale grading development; to estab

lish criteria (including specifications) whereby safe

and stable mass grading could be accomplished; and to

establish foundation d~~-~ criteria for 2!1~- and E!9-s~ res id~tial s tru~es.

Scope

The Soil Investigation of the Westborough property has

resulted in a detailed drilling program to establish the

areal extent and uniformity of the subsurface materials~

Samples were obtained from which the materials were. mea

sured by means of extensive laboratory tests. Results of

the foregoing studies, along with the information gained

from a geologic inspection of the property, were used in

analyses from which the appropriate recoII1II1endations and

conclusions were made. -

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File No. £2204-Ml 30 November 1964

In addition to the presentation of a single investigation

report, the soil engineering services were extended through

out the subsequent construction work so that supplemental

studies and.recommendat.i-9Ils could be made as the need arose.

Authority

The original work was conducted under the auspices of a

contract; dated 13 April 1960, executed between Pen'insula

Testing and ConJ;i:gkJ~. (our former firm name) and_ Callan

Park Homes, Inc.

i?ubseguent wo:tls has been conducted on the basis of verbal

authorization from Westborough HOi:!!eS, Inc. and has been per

formed on a Fee Schedule basis, in accordance with the rates

applicable at the time the work is being performed.

Personnel

For Westborough Homes, general direction has been given by

.Mr. Michael C. Callaq, assisted at various times by Messrs.

FE!-n~kht__s, Dwili(;ht Ph.illiP.fi_and Jorgen ~und;i,p&:..., Engi

neering for the project has'been provided by the' offices of

~~~ore V. Tronoft, Daly City, and Wilsey. H_IPll and Blair,

San Mateo, California.

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For Gribaldo, Jacobs, Jones and Associates, the work has

been supervised by Mr. William F. Jones, Principal, as

sisted by~ K. Crosby, P~r M. M.QB..k, D~ M. Wilson,

and Philip V. B~, Engineers and Geologists. Others

who contributed to the investigations as technicians were

l',~E~ Brown llnd William Bontadelli.

Dr. :frank W, Atchley, Consulting Geolog!:.!$, has provided

valuable assistance through his observations and indepen

dent reports on the property.

History

At the time the original work was authorized, Callan Park

(Westborough) had been annexed to Daly City, and the engi

neers were involved in preparing a. street and grading plan

conforming to.the ordinances of that city. Problems of

timing required that. soil reports be available at an early

date for a proposed water storage reservoir and for Unit

No. 1 of Callan Park (Westborough). Accordingly, the field

drilling for the reservoir and Unit No. 1 was executed

first, with the field work for the balance of the area con

tinuing while the laboratory testing and analysis was con

ducted, leading to the following reports:

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1. "Preliminary.Soil Investigation for Callan Park Unit

No. 1; Daly Ci_ty, California," dated 12 May 1960.

2. "Subsoil Investigation .for the Proposed DiummAvenue

Reservoir, Callan Park," dated 7 June 1960 . . .

The remainder of work 11eeded to complete the original

report, including preparation of a written draft, was com-- ,: '

pleted by 7 July 1960. However, it was then appari:mt that

the validity of the proceedings by which Callan Park

(Westborough) was·annexed to Daly City was to be questioned

by a referendum vote. Production of the original report

was thus withheld until the influence could be seen of de-

velopment according to CO\lnty standards, involving larger

lot sizes than permitted by Daly City. By the time the

referendum was held reversing the annexation proceedings,

it was clear that development to Cot.mty standards would not

significantly effect either the general concepts of street

layout or the general locations and magnitudes of. proposed·

cut and fill operations. The 1_260 report was subsequently

issued with references to San Mateo County, even though the

original Site Plan reflected tentative street layouts in ac

cordance with Daly City standards.

The Westborough property has now recently been annexed to

South San Francisco, and a new DeveloP1!1ent Plan, prepared as

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is shown in Figure No. l. This plan reflects changes in

eroposed land use and structural improvements; but in no

way requires changes in the-basic rec0111111endations pre

sented in our 1960 report •. Nevertheless, because of these

changes in overall concept, it was felt that an updating

of the Soil Investigation Report was-in order. We have

therefore, taken this opportunity to 'include in this re

port findings of the more recent investigations as well as

those of the original investigation. In addition, we have

had an opportunity to do further research and appraisal of

the potential hazards of d~velopmeht that may exist because

of the p~oximltl; of the San Andreas Fault zone and its re

corded history of earthquakes. A discussion of this sub

ject by ~rir:_ Frank Atchiey, Consulting Geologist, is -in

cluded in this report aiii ~p,pendix D. _,

Synopsis

The Soil Investigation of the Westborough property has re

quired an @Xtensive drilling program to determine the sub

surface conditions_ over the property, and to obtain soil

samples for laboratory testing. Where the qualities of

the soils were suspect, or where the proposed loading made

it desirable to develop maximum information, additional

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drill holes were advanced. Special attention has been

given to the area designated in the Report as Zone II.

Thts major trough, which represents a topographic ex

pression of the San Andreas Rift Zone. was character-. I_

ized by major problems of drainage and soil stabilit"(,

and contained deep deposits of clay and/or highly <~ . .--;

organic soils.

Three major soil or geologic zones are defined in the ' -Report. Zone I occupies the extreme westerly portion . p •

of the pi:'operty,,and is characterized by the rocks and

residually derived soils of the Franciscan formation.

TJ;iese materials are badly weathered, altered, and

pheare4, il!.trusive-type rocks with many serpentine . . -

bodf,.e.s and numerous sP.,rings. ZoJ!e II was occupie.d by .

tectonic sag ponds,. some of which had been artificially

dammed to increase their water storage capacity, and

deposits of soft ~ilts and clays. The--ponds typically .. ' . -

are filled with deep deposits of s9ftpeat. •

Zone III, .

which comprises the majority of the Westborough property,

consists of the unconsolidated sediments of the Merced

f~rmation. Typically they are i:!!!'rin~ d~gosits 'o~ ~'

!!!.t and clay :With ll!.!:nQr limestone beds. These mate

rials have good strength characteristics and are consid-

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ered ~on-expansix.e ,!O moderately exe.;Jna;\Ju! as foundation

soils. They are, however, e~sily. erodible and must be

protected fr_om _the effects of erosive forces. Locally

within Zone III, t~s of o:i:..~o:_ni~~ll,y contami

nated topsnjls occupy the s~ and draws.

Development of the property can be accomplished by mass

grading. Requirements and specifications for grading

are presented in the Report. These requirements call

for extens:f,ye remoya_l of unsuitable soils in areas to '

be filled; installation of e.3tensive subdrainage facili-

.t.ie.s; and the construction of fills to current· standards _..

of compaction. Detailed recommendations are presented

for the construction of safe slopes as well as other

features related to grading.

On the b_asis of· the strength properties of the soils, spe

cific recommendations for design of foundations for ~

a~. two-stg;:y;. resi,Qmt;l.§1 structures are presented. It

is shown that conventional foundation types may be uti

lized under normal conditions of loading and lot develop-

ment.

In development of the Westborough property, the potential

~!_d of earthquake,damagi:.._must be fully recognized. The

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File No. E2204•Ml 30 November 1964

report shows that the line ·of s,urface rupture that took

place during the !2.Qi earthquake gasses through the l!.!S!.

~r,EY (coincidental wit~ ?:,_one !~) and that future earth

quakes of large enough magnitude could result in further

g~ound movemi;AI:.,. A detailed report which discusses the

hazards associated with seismic activity bas been pre

pared by Dr. Frank Atchlex, Consulting'Geologtst, and is

included in the report as Appendix D. It is one of the

purposes of this report to point out that this hazard

exists, as it does at many places within the· San' Fran•

ctsco Bay Area. Once the hazards are made known, it is

then considered the ~ of the Owner-Deyeloper ·- .. ,

and the 1,5!,cal goverllll\ental as.~cte!- -~ e,11t;iRJ;i,.a.h ~

:iJ.mitatio!l~!.. on development. Reconunendations toward this . ' '

end are p:i;esented in-both Dr. Atchley~s.report and .the

Soil Report. One of these recommendations, particularly

related to the pr<?posed \!!;st Park Development,. ~-s- t-~~1: , _

" ••. final proj e~t ·,planning of. structu~e orientation.' ar-' - ' ,,_,

rangemer\t l!!ld de"sign b~ _ceftified by a St:r;uctyral En~-

~ With a rl!!,COgniz~d eminent stature !.,n earthquake. ~

~gp.. '' This may well be applied·- to a~ other than the

We~ Development also. _..... ..

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TABLE OF CONTENTS

LETTER ON EARTHQUAKE DESIGN CRITERION

LETTER OF TRANSMITTAL

PREFACE

Object Scope Authority Personnel History Synopsis

SECTION ONE ~ LOCATION AND DESCRIPTION OF SITE

1.1 Location 1.2 Site Description i.3 Intended Use of Site

SECTION TWO ~ FIELD INVESTIGATIONS

2.1 Reconnaissance 2.2 Subsurface Drilling (1960) 2.3 Special Investigations (1960) 2.4 Special Investigations (Post. 1960)

2.41 Apartment Site at Oakmont Drive and Westborough Boulevard

2.42 Proposed Storage Reservoir Sites 2.43 Slope Easterly of Skyline Boulevard 2.44 Cut Slopes in Unit No. 3 2.45 Sag Ponds in Unit No. 5

(xiii)

Page No.

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(vi) (vi) (vii) (ix)

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File No. E2204-Ml ll 30 November 1964

SECTION THREE ~ LABORATORY TESTING

3.1 General Testing (1960) • 3.2 Corrosivity Tests (1960) 3.3 Special or Additional Testing (Post 1960)

SECTION FOUR ~ SOIL AND GEOLOGIC CONDITIONS

4.1 Regional Geologic Setting .4.2 Site Geology and Topography 4.3 Soil and Geologic Units

4.31 Zone I, Skyline Area 4.32 Zone II, Major Trough Area 4.33 Zone III, Easterly Area

SECTION FIVE ~ DISCUSSIONS, CONCLUSIONS AND RECGIMENDATIONS

5.1 Introduction 5.2 General Recommendations .(1960)

5.21 Grading and Site Development 5.22 Drainage 5.23 Slope Stability 5.24 Residential Construction 5.25 Metal Conduits

5.3 Results of Specific Studies (1960) 5.31 Apartment Site at Oakmont Drive

and Westborough Boulevard 5.32 The Major Trough (Zone II) 5.33 Drainage Swales in Zone III 5.34 Treatment of Limestone Deposits

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15 16 18 18 20 21

25 26 26 29 31 34 37

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5. 4 Results o.f Specific Studies (Poat 1960) s.41 Introduction 5.42 Apartment Site at Oakmont Drive

and Westborough Boulevard

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5.43 Proposed Storage Reservoir Sites 46 5.44 Slope Studies 47 5.45 Sag Ponds in Zone II 5.46 Street Pavements •,

5.47 Settlement Analyses 5.48 Seismic Hazard

52 52 55 57

5.5 Limitations.and Uniformity of Conditions 60

LIST OF TABLES

TABLE I - Summary of Corrosivity Test Results 13 TABLE II Generalized Requirements for Street 54

Pavement Design TABLE III Sutnlllary of Moisture Content, Dry 63

Density and Shear Test Results TABLE IV - Summary of Laboratory Compaction and 66

Shear Test Results on Disturbed Samples

TABLE V - Summary of Swell Test Results TABLE VI - Summary of Direct Shear Test Results

for Slope Studies ~ Westborough Unit No. 4

TABLE VII - Summary of Laboratory Test Results on Typical Zone III Fill Material Placed at West Park Units 1 and 2

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LIST OF FIGURES

Figure No. l - Development Plan

Figure No. 2 - . Location Map Figure No. 3 - Site Plan

Figure· No. 4 - Subdrain Layout

Figures No. 5 through 9 - Moisture-Density Relationship Curves

Figures No. 10 throngh 12 - Consolidation Test Data

Figures No. 13 through 36 - Logs of Test Borings No. l through 89

APPENDICES

Appendix A Labo~atory Test Results

Appendix B - Logs of Te.st Borings

Appendix C - RecOllllnended Grading Specifications - Guide Specifications for Base Rock

under Concrete Slabs

Appendix D - Report on Earthquake Hazard by Dr. Frank W. Atchley, Consulting Geologist

(xvi)

Page No.

Pocket - Inside Back Cover

(xviii) Pocket - Inside

Back Cover Pocket - Inside

Back Cover 71 through 75

77 through 79

83 through 106

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30 November 1964

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Figure No. 2 - LOCATION MAP

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SECTION ONE LOCATION AND DESCRIPTION OF SITE

1.1 Location

The Westborough property consists of approximately 650

ac:res of hilly terrain located in northern San Mateo

County within the old Buri Buri'llan_cho: As show on

the ''Location Map." Figure. No.· _2. the westeriy boundary

of the property is Skyline Boulevard, while_ the easterly

limit is Junipero Serra Boulevard •. The irregular. south

ern boundary is common with the limits of the City of San

Bruno, while the northern boundary of Westbox-'ough is com-.·-.

mon with other !lndeveloped lands within San Mateo County,

. most of which were once. Lands of. Christen~

1.2 Site Description

The property is composed of rolling hills and well-de

fine4· drainage channels, ·forming the :western portion of

the Twelvemile Creek Drainage Bas.in. Prior to 1960 the

. property had been used fox- truck farming and the pastur

ing of cattle, Several groups of hODleS and outbuildings,

associated with the farming activities, were located

within th~ area of inves.tigation. Numerous water wells

and several active springs were noted on the property.

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The locations of three of the water wells are indicated

on the "Site Plan," Figure No. 3; enclosed in the pocket

at the end of this report. Several ponds, some of which

have been artificially formed, were noted throughout the

property. Many of these are also shown on Figure No. 3.

Most of the ponds are natural sag ponds within the San ~ ' ' ~

Andreas Rift zone. Utility lines and easements of both '

the North Coast County Water District and Pacific Gas

and Electric Compan~ cross the site at various locations.

1.3 Intended Use of Site

The investigation of 1960 was conducted on the basis of

a preliminary plan for the property which called for pri

marily single-family residential development requiring

extensive and massive grading. Subsequent development

plans have not altered the grading concept appreciably so ' '

that site devetopn;ent still requires extensive grading and

earth moving. Subsequent plans for structural improvement

indicate that more of the site may be occupied by ~1;1ltiple-. -

family structures and commercial developments than was or'i

ginally considered. The primary recommendations contained ·'

herein are for the execution of hillside grading, whether

it be for single-family residential structures or any other

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The reco1D1Dendations for foundation design as presented

in this report are limited to ~- ~r two-sto~ sj.ngle

family residential structures. Any structures different

from that will r!!quire ad_ditionaj_studies and 's.!lparate 4

recOlllDlendations depending on the s.f!.e, tl!?.e ~nd exact

location of the particular structure.

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SECTION TWO ~ FIELD INVESTIGATIONS

2.1 Reconnaissance


The first step in the field investigation was a thorough

site inspection by an engineering geologist. The prop

erty was fully studied and such features as topography, ., draina_ge, vegetation and improvements were noted. At

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the same time, areas of potential soil problems, such as

~_!~age a~~~. oversteepened banks anq deposits of highly

~rganic mater~al, were noted. It was on the basis of ,.

this preliminary. inspection that the subsurface drilling

program was laid out.

2.2 Subsurface Drilling (1960)

The. 1960 driJ:,lifl$ program was carried out to give adequate

general.cover~~e of the subsurface soil conditions. Addi· --t;!_~al bgrJn,g~ were scheduled at all points where. known

~~ existed or ~here sP._ecific inf~was desired~

The cµ;;iginal investigative work resulted in the drilling

of J±._!~st b9ritl~• the locations of which are indicated

on Figure No. 3. All borings, except Nos. 27, 28 and 29, l'-- _._ "'

were made with a truck-mount~_ti:._g, using l!J~;.;luch."""di.ame.t,eJ:..

c;,gp.J;,!..nugµs .UJ,gbt; aJ.l~. The three exceptions were drilled

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with a hand powered, wash boring rig using shelby tubes

for sampling, while the regular borings utilized a 2-1/2

inch O.D. split-spoon sampler for obtaining "undisturb

ed" samples. As the borings were made, ~ogl!_ were kept,

showing the depths and thicknesses of materials encoun

tered and the locations of "~isturbed" samples. The

~.08~ of the borings made for the 1960 investigation are

represented graphically as Figures No. 13 through 36,

presented in Appendix B. -The known borrow ar~ were sampled for laboratory test

ing to determine the properties of the soil when recom

pacted. The locations of d!!E.!:Irbed sa~s are shown as

D-1 through D-5 on Figure No. 3. -- - .

2.3· ·Special Investigations (1960)

Three special investigations were made at various loca

tions throughout the site during the initial work of the

1960 investigation. The first consisted of tl:i.ree test

holes (Nos. 50 through 52) drilled in giid area 8-J and

8-K, as shown on the grid of the Site Plan. These holes

were drilled to determine the soil conditions at the pro-

posed site of a water storage reservoir. The second was

a series of three holes (Nos. 27, 28 and 29) to check the

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depth of the <;>rsanic deposits in ~o pon4s in the north

west corner of the property. The third was to check the

elttent of a lj.mestone conglomerate. The latter investi

gation consisted of a surface inspection by an engineer-

ing geologist and the drilling of o,ne test hole (No, 32).

2.4 Special Investigations (Post 1960)

2.41 -!Y>artment Site. at Oakmont Drive and Westborough

Boulevard

In J_uly 1963 a specific Soil Investigation was made of

the proposed apartment site southwesterly of the inter

section of Oakmont Drive and Westborough Boulevard. As

indicated in the 1960 report, the east facing sloee in

this particular area showed signs of instability and a

significant program of !!lope recoti.struc,tion -and stabili-'

zation was recommended. As of this. writing that recon

struction has not yet beep. ac~ompli~he£._. In fact; the

gaster~ haU of V{~.§_tbqt_q__~((IX~~ (where it is un

improved above Oakmont Drive) is ·undexl ai n by fi 11 which --is µpacceptahle..,. and which m.!:lBt be remoy~g and incorpor

ated into a reconstruction program for the entire slope.


The purpose of this special investigation then was to

establish criteria by which Westborough Boulevard

could be completed and by which the. 10-acre site could

be developed utilizing terraced, hillside sites for

apartment pads. ~4!!!.t...i.QD.Jll~ test borings were dril

led at this site in J,9,6J.. They are Nos . ..f>3 through ~7,

located on Figure No. 3. Their logs are represented

graphically on Figures No. 26 and 27, presented in Ap

pendix B. A detailed report of that investigation was

issued under separate cover in July 19§J. A sunnnarized

discussion of the basic conclusions contained in that

report is included in Subsection 5.42 of this report.

2.42 Proposed Storage Reservoir Sites

In October 1963 several subsurface investigations were

made in the westerly end of grids ,7-J and ·s-J for the

Westborough County Water District. The purpose of these

investigations was to establish a location of suitable

foundation condit;ions for a l.arge water storage rese~

voir. The results. of those studies· cannot be included -~

in this report, but the findings proved helpful in gain

ing added information regarding subsurface geologic and

ground water conditions in that particular area.

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2.43 Slope Easterly of Skyline Boulevard

In January 1964 a detailed investigi.titm of the subsur

face soil and geolggic cg_ruJ.itigns along the east faciiu; ' . .

sloee easterly of Skyl;i.n~ Boulevard was undertaken after

it was learned that a significant cut was proposed for

that area. Six test borings were made along the area of

proposed cut to depths ranging from 26 to 73 feet. The

locations of these borings (Nos. 2§. th~-6A) are shown

on Figure No. 3, .while their logs are presented graphi

cally on Figures No. 27 through 29, presented in Appendix

B. Rec0Im11endations culminating from the results of the

above described investigation were presented in various

correspondence to Westborough Homes. They are summarized

in Subsection 5.44 of this report. --2.44 Cut Slopes in Unit No. 3

In March 1964 several borings were made in the then com

pleted Unit No. 3 of the Westborough subdivision. The

purpose of that investigation was to explore the soil con

ditions along the numerous cut embankments. The locations

of the additional borings (Nos. §!!- through §J) are shown . \

in the area of Unit No. 3 on Figure No. 3, while their logs

are presented on Figures No. 27 through 34, presented in

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Appendix B. Results of this additional investigation

are discussed briefly in Subsection 5.44 of this report.

2.45 Sag Ponds in Unit No. 5

During the grading operations which are currently under-...

way in Unit No, 5 (now referred to as West Park Planned

Community), it became necessary to make additional bor

ings in the organic deposits o.f the ponds in the north

westerly corner of the property. The purpose of the

borings was to more accurately define the depths and

areal extent to which excavation of the organic sediments

was to be made. Results of these borings (Nos . E through

Jill on Figure No. 3) were used to control and direct the

grading operations in that area. Logs of the above des

cribed borings are presented on Figures No. 34. through 36,

presented in Appendix B.

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SECTION THREE ~. LABORATORY TESTING

3.1 General Testing (1960)


The laboratory testing was organized to ~ive information

on the strength and bearing properties of the soil; on

the suitability of material proposed for use in fill; on

the extent of shrinkage or swell in recompacted soil; and

on the corrosivity of the soil in the seepage zones.

Strength parameters from which bearing values and stability

factors could be established were obtained from results of ·

direct shear tests. Undisturbed specimens of the soil were

placed in contact with water for a minimum of 24 hours and

then allowed to drain before and during the shearing. The

same test was performed on soil to be used for compacted

fill. The soil was first prepared by remoulding disturbed

samples to the same density specified for compacted fill.

These specimens were similarly soaked and drained, and then

sheared under normal loads ranging from 1,000 to 4,000 p.s.f.

The materials proposed for use as fill were subjected to the

laboratory compaction test, A, S. T. M. Dl557-58T, Method A,

by which their maximum dry densities and optimum moisture

contents for use in field control of fill operations were de-

termined.

File No. E2204.-Ml 30 November 1964

Undisturbed samples were tested for their.in-place mois

ture content and dry density. These were measured by

weighing a known volume of soil before and after oven

drying. The average dry density of the in-place soil was

compared to the specified density for fill from the above

test. This comparison indicated the relative shrinkage

or swell factor of the soil when placed as compacted fill.

Expansion properties of the soils were determined by com

paring the percentage of volume increase to percentage of

moisture increase as measured from the direct shear test.

The results of the foregoing tests are shown summarized in

TABLES III, IV and V, presented in Appendix A. The com

paction test.results are shown graphically in Figures No.

5 through 9, presented in Appendix A.

3 .. 2 Corrosivity Tests (1960)

To establish their potential corrosivity on underground

metal conduits, tests were performed on soils taken.from

Unit No. 1 of Westborough. The selected procedure was

that referred to as the Williams-Corfield nipple-and-can

test, in which the loss in weight the n.ipple suffers is

considered as proportional to the maximum potential cor

rosiveness of the soil, and is termed the Corrosion Index

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Number. Classifications have been arbitrarily determined

as follows:

Corfield Corrosivity Index

Corrosion Index Nu~ber . (Weight Loss of Specimen)

Corrosivity of Soil

3 gm. or ,over '

2. 00 to 2. ~9 gm.

1.00 to 1.99 gm.

Less than. 1.00 gm.

Very severe

Severe

Moderate

Low

The results of the tests performed in_ this manner are

shown in TABLE I.

Sample No.

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TABLE I

Summary of Corrosivity Test Results

Williams~Corfield Method

Corrosion Index Number

0.85

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Corrosivity of Soil

Low

Moderate


3.3 Special or Additional Testing (Post 1960)

Subsequent to the initial. testing program as described

above, ~utnerous routine tests of soil properties have

been made. These have included laboratory compaction·

tests (necessary for.proper testing and inspection of

grading operations); direct shear tests~ on both un

disturbed and recompacted soil samples; in-place mois

ture density determinations of samples taken during ad

ditional investigative studies; and a recently completed

series of tests from which settlement characteristics and

permeability data could be obtained. Results of any sig

nificant testing subsequent to- the 1960 work are presen

ted in 'UJHFS Y! and Y!J, and in Figures No, 10 through

12, presented in Appendix A.

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SECTION FOUR ~ SOIL AND GEOLOGIC CONDITIONS

4.1 Regional Geologic Setting

The Westborough property is located on the easterly flank

of the northwest-southeast trending coastal mountain range

that forms the San Francisco Peninsula. Within this gen

eral area of the Peninsula, some 10 miles south of San

Francisco, its westerly portion is made .. up of consolidated --~~..:.....:.~~·~I- .

rocks of the Franciscan formation 'of Cretacegu~ and J~;as~

~ age, while. its ~ste~!:i portion is made up of uncon

solidated rocks of the Merced and Colma fqxmatign.s of

r1iocgne and P~stocene a~e. To the northeast, beyond

the Merced and Colma materials, Fran_GJ,~ rocks outcrop

again in the vicinity of San B~E£>Ji'l4'!}~~~-·

The Fi;ancil!J;:.ilfl formation in this general area of the

Peninsula consists. of interbedded s_imdsto,n_e and ~h,1i!,,l&;

chert interbedded with shale; and greenstone (al;ered ~~

~lt!.£ rocks). Basic and ultrabasic intrusive rocks, pre

dominantly s~pentine and diabas~ are often associated with

the Franciscan rocks.

The tl~d formation consists mostly of friable to firm

~al!_d, ~£~ and ~1~Y. Locally, l,imeeJ:;p_i;Jg...§.!l,gll..~bA~&,U;.

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The Merced unconformably overljes, g;r is in. fault contact

with, the Franciscan formation. The Merced formation is

in turn unconformably overlain.J:!y the Colma formation,

·which consists mostly of friable well-sorted s.and.

4.2 Site Geology and Topography

Within the Westborough property only the Franciscan and

Herced formations are exposed. They are clearly separated,

near the westerly boundary of the property·, J:?y the trace

of the SJ!n_Ali,ch;ga§ F;:w,l!:. This northwest-southeast trend

ing ~1,;..J;Q:\}e is well-expressed topographically along most

of its length by a well-defined lineation of valleys and

canyons and numerous sag-ponds, and includes the deep, nar

row canyon that parallels Skyline Boulevard some 600 to

900 feet easterly of Skyline at this particular location ..

The area along Skyline and eJU;ending easterly ~ what shall

be referred to as the major trough, is composed of rocks of -the Franciscan formation and their weathered products, while

the remaining majority of the property which !!_es easterl.1

of the fault trace, is characterized by the ~ and silts

of the Merced formation. A detailed description of the

geologic formations and the soil units derived from them is

included in Subsection 4.3.

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Topographically, the property grades downward from an

elevation of 675+ at the westerly limit to a low of

approximately elevation 150 where Twelvemile Creek

. drained beneath Junipero Serra Boulevard. Except near

the westerly boundary where the drainage is controlled

by the northwest-southeast trending fault zone, drain-,

age of the property is to the east through two major

drainage channels: one at the northern boundary of the

property; and the other at the upper reaches .. of Twelve

mile Creek in the central portion of the property; · Be

cause of the ~rosivenature of the ~reed folj]latioq_,

several significant contributory channels feed into the

two main easterly-draining canyons. Other significant:

drainage .swales exist near the easterly property line

leading down to Junipero Serra Boulevard.

Within the fault zone, or major trough, near the westerly

limit of the property, draiDa,ge has been dist'Upted by

fault mov.ament, resultu;,g in.the formation of numerous

"sag pond;;" along the trough. Over the;years these ponds

have accumulated several feet of '?rganic sediments of a

true "peat" composition. Widespread spring activity was

noted within the property, particularly along the ~t

zone, by' the presence of ]Nater wells and surface seeQ.S in

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that area. ~pring activity of a lesser nature was ~.

poted in localized areas within the Merced formation

easterly of the fault zone.

4.3 Soil and Geologic Units

Despite its large area, the Westborough property can

easily be divided into areas of well-defined soil types.

In the 1960 report four zones were described, with the

third zone being subdivided into Zones III-A and III-B.

For this report only Zones I, II and III will be used,

with Zones III-A, III-B and IV described as units within

Zone III. · The approKimate boundaries of the three zones

are shown on Figure No. 3.

4.31 Zone I, Skyline Area

Zgne I is the easterly sloping area between Skyli.ne

Boulevard llJld the major trough of the San Andreas Fau.JJ;. ~

It eKtends easterly from Skyline Boulevard approKimately

600 to 900 feet and ~orms the westerli wall of the canyon

that parall~ls s~~-

The t2£.ks of Zone I are typically medium to dark brown,

badly weathered ~~d ~hattere~ rocks of the Franciscan ~ . '

formation. Because of the shearing and fracturing affect

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of the fault movement that has taken place throughout

geologic and recent history, the ~ocks are highly al

tered and weathered. These rocks were originally des

cribed in our 1960 report as weathered shales with

local serpentine intrusions, but closer examination

with the aid of deep excavation and additional borings,

indicates they are primarily altered basaltic rocks,

often referred to as ~eenston~. The weathering has

produced highly fractured rock fragments o.f variable

size and soundness in a matrix of brown clay. The

weal;berfng is variable too, so that the amount of clay

ranges frorn only minor _clay seams and clayey coatings

·in a firm rock mass ·.to pockets of nearly all clay with

minor rock fragments remaining. In addition to the

weathered clay .of the parent ro~k, serpentine zones are

common in this area. Soft, bJ,ue.,gray to greenish.,gray

clay and shattered serpentine rock have been encountered ,.

at shallow depth in Zone I. Ground water is quite com-•

' manly aJ!_sociated with these s~rp_entine bodies·. and was

found in several borings made in that zone.

Because of the nature of the rock· in this zone and the

presence of clay seams or pockets and ~ SJ~~]~gntine.

bodies within the rock, ~nes of w~~Jutess exist which

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~ cause structural failure Qf £!1,t or natural slopes /

where the orientation of the zone of weakness is ad-

verse.

The majority of the Zone I materials, because of their

clay content and the weakened na'ture of the rock par

ticles, will result in moderately ex0ansive sotl of

moderate strength when placed as compacted fill. Re

cent tests on the Zone I material show it to be of

generally poor quality ~r use as subgrade soil in

street pavement sections.

4.32 Zone II, Major Trough Area

Zone_ II, as shown on Figure No. 3, is defined as the

transition zone between Zone I to the west and Zone Ill

to·the east; It consists primarily of sediments on the

floor of the well-defined valley, referred to as the

,ll@jor trough, which reflects the trace of the San Andreas

~t. Within this trough or valley, particularly near

the northern and southern limits of the Westborough pro

perty, horizontal displacements of the ground surface

were in evidence following the e~rthquake of 1906. The "o--

total offset of a fence crossing the line of fault move---ment within this trough is reported to be 13 feet, with

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the westerly side moving noJ>,th with respect to the

easterly side. Displacements of similar magnitudes

are well documented along this portion of the San

Andreas Fault as a result of the 1906 movement.

The valley floor was characterized by deposits of ' ~-

Qiganic silt and isolated ponds of water, which col-

lected surface and subsurface waters .. Two of the

ponds had been dammed ~o increase their storage capa

city and to provide a source of irrigation water. The

soil in the valley floor is generally a clay silt or

silty clay with varying amounts of organic matter. In

the bottom of the two northerly ponds, the or.ganic con

tent is so high that the material is classified as true

peat. The moisture contents of nearly all the soils

within the trough were near or at the s~:t.a.t;.iQ,a. 'level.

4.33 Zone III, Easterly Area .__

The remainder of the Westborough property eas·t of the

fault trough. is composed of the unconsolidated rocks of

the. Merced formation. They are marine. deposits gf sand 1.

til,t and clay,. which have not been sufficiently indur-' ated to produce hard sandstones,' but which have been suf-

ficiently cemented in most cases to allow steep embank-

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ments to stand for short periods of time before ero

sional forces wear them down. The poorly defined bed

ding of the Merced formation indicates, where measur

able, an approximate strike of N 30° W with a dip of

approximately 30°.to the northeast.

Even though the sands and silts of the Merced forma

tion, excluding the organic and topsoil deposits in

the canyons and draws, are firm, dense materials, - -only slightly to mpderately e~p<m§i~e and having good

strength properties; they are V!.Sf friablE:, making

them ~~sceptible to erosion. The erodable nature of i

the Zone III materials is well evidenced by the num~ I

erous and deep erosion scars. The high silt content

of the Zone III materials presents a problem of silt

contamination where runoff is allowed to flow over

these soils unchecked.

There are numerous areas within Zone Ill where deep ~

deposits of soft silt and organic sedimepts, have w:,.

cumulated, These areas include the lower reaches of

drainage swales which lead to Junipero Serra Boulevard.

Boring No. 49, which was drilled in the bottom of the

Twelvemile Creek canyon near Junipero Serra Boulevard,

revealed nearly 30 feet of saturated, low density, com~

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pressible sandy silt. Subsequent investigation of the

canyon indicated that the condition revealed by Boring

No. 49 was a very localized "pot-hole" condition, and

that the typical depth of loose sediment in the canyon

bottom was on the order of five feet or less. -Other areas of significant organic or soft deposits in

clude the two swales in the vicinity of Borings No. 34 -and 39, near Junipero Serra Boulevard. These borings

encountered SQft Sil.ts to depths of .JA. and 8 f~t, res

pectively.

Also included within the Zone III materials are.local

ized strata of limest2ne conglomerate in the southeast

erly portion of the property. These beds, composed pri

~arily of Nell-cemented stutll fragments, are. more resis

tant to weathering than the surrounding.sands and silts

and thus stand out on the hills in the vicinity of Bor

ing No. 32 as.lines or large piles of light $ray rock.

Many of the rock pieces have broken loose from their

original position and moved downhill under the force of

gravity and weathering processes. The resulting scat

tering of the large limestone rocks gives an impression

of a much more extensive deposit than actually exists.

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The conglomerate beds are composed of nearly a11 shell

fragments and whole shells near the center of each bed.

The beds become thinner toward either end of the deposit,

grading into sand and fine gravel material. At the ex

treme ends, the beds grade into pure sands, indicating

a localized condition of deposition. The limestone rock

is hard where fresh, but somewhat soft and porous where

,it is exposed to weathering. These limestone materials

crop out primarily in areas of proposed excavation, and

will probably produce many large rocks ~h will £!.- ·

quire special handling in the grading qperation.

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File No.· E2204-Ml 30 November 1964

SECTION FIVE ~ DISCUSSIONS, CONCLUSIONS AND RECOMMENDATIONS

5.1 Introduction

The Westborough property is, in general, characterized by

materials which can provide suitable foundation conditions

. for the proposed residential, commercial, and educational

development. However, as is common for nearly all exten

sive mass grading proposals in the hilly terrain of the

San Francisco Peninsula, numerous problems exist. The sig

nificance of these problems can be reduced, and in most

cases eliminated by the employment of sound engineering and

construction practices. The one factor which cannot be eli

minated is the potent ii!}. ha~.m;.4, of seismic activity due to

earthguak.~· As is the case for any development in the San

Francisco Bay area, or in fact for any development along the

Pacific Coast, an unknown element of risk with respect to

earthquake hazard is always present. The effect of seismic

forces on earth embankments and filled ground has been·con-- --'sidered in our analyses and studies from which the following

conclusions and recommendations were drawn. In all cases,

current standards of seismic factors and their application

have been followed for this project. A more detailed discus

sion of potential seismic hazard and recommendations ·relating

to it, is included in Subsection 5.48.

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5.2 General Recommendations (1960)

5.21 Grading and Site Development

The great majority of material to be used for fill con

struction on this project consists of the yellow-brown

sand and silt f~ Zone III. These are highly suitable

engineering soils and provide an excellent source of

borrow for f.JJ..l .materials. Similarly, areas of proposed

fill placement can be made suitable for the support of

such fills, provided the. requirements and recommendations

set forth in this report are followed. Included in ,&p.,,

p_endix g are "!S~~q.4.~.9...Q!.1!2_in&...§a~:!,!!,!;:gJ;io~," which

set forth minimum standards necessary to satisfy other

requirements of this report. Without ~ertificatio~ o.J

complian£il with those specifications,.design criteria as - '

presented in this report must be considered invalid.

Nearly all areas where !!9ft, saturaJ;_~d....§pil;;i existed in

any significant quantity have, or will, become filled

land. ·Consequently, consideration of these as foundation

soils for direct support of structures was unnecessary.

It was necessary, however, to consider the t!!.§tment re

quired to make these areas s':!tabl_e f!J.r the s~f-~,,:,~),1pp_9£J:

of" Jj,J:l. The lar_gest ~!E£sits of s~ COil!?.2:!.~~J-1'. .. !,!;,~ so.il

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were in the c_any_on b9_t;.t2!!!._ o}' Zi,m_e-II. Their treatment

is discussed in detail in a later Subsection. Else

where, the deposits are of shallow depth and generally

confined to localized pockets. In most cases, the.ma--terial_s are to be remos.~c;I by over-excavating ~d back

filling with suitable ~~.!!].· In certain areas the

softer_ soils 1!18:Y be J,.~JU!l:;JW!s.e, <!-E.a~i;i~~. with exten

sive herring-bone subdraina.z.e facilites, and consoli

dated by means of e_;:e!g~£!..in,g with cg~E-~~-illl of

prescribed dimensions f~! a pr~~.s-~;f,p~~ ... P~A.~4,,,,a..t.ll!!!!·

The Soft sms, c,~Y.S, 'l!J!il Ol,.&!,~}..$,,!£<~!;i found in the

poE-E:~s, c;.:hannels ~l!K.~J&s may_Q.~...;.IJ...§,fi_d in_J..!!.,~ areas,

PJ:C>Y.lc;IJ!d they are placed in laye:s ~at ~~-~~g -~

~~es in compacted thickness, S_!ndwic!w,i;l...h~~lil.tl t<il.X.;;..

~s of the brown silty sanqs at;_Jeast t.w_Q,.,.fgg,t in thi_s)S

ness. These soi~s are only to be placed in areas where

they can ~~~ after placement for at least tJ:;iree 11)01!,,th!!

\1~£9.!e construction of ;~,s_!i;!..~~A or other structures.

Further, the soft soils excavated from the ponds and

swales m\!St 1/''!£~_J;>J,~g_e.d wj.~l1Jn f~~~-'f'l(;lt e! f,;i.E'ishe~d

grade, including the face of any slope. Similarly, the .X,"ii'~.IMf'EI,

mft, b~y.J\~gl;'.!'!.~ S~;:E!!}lt.t!!g~SlUs f()t,!.r,t<;L_:i,n Z.Q!:t~,,.}, ~t

n~;~_be P.l-~_e~d wit:\11n t?!?. f~.t o:t; _ _Jil}!~l!~g_,$!."!-c.!,1'!, nor_.

within five feet of the surface of any sJ,RJt-~.· ~..., ... ~"'--·----~·"'""""'.ilnlllll- .... , . '

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As indicated in the "Recommended Grading Specifications,"

clearing, grubbing and stripping will require extensive

and careful operations to remove all treji!§_, brush, roots - --and debris from areas to receive g111. Clearing and ______ .. '

stripp_ing is to be d~e to the satisfactlon ~ the Soil

~nginG~..f before fill is placed in any particular area.

Particular attention must be given to the provision of

"!4equ~J<.ex;i where fill is to be placed on the hi,llsf,g~

~J.gpe;;i ~ !a___ the c~~.

fills and side-slope fills,

At the toes of the canyon

the base key should be at ~!Ill: ~ '"

1_£asta.?O ;t;es,S,. in w!!;l.S!1• cut into firm natural ground,

and s):9ped ha~ into the hillside at a gradient of not

less than 3!· Subsequent ~ey:s should be cut at v~e;i;-Nti~~~

1*!ghts of n~t-SP.'!;li! th~n .. Jl ... fJM~.i; ..

Very little volume change is expected for the materials

on the Westborough property when excavated and placed as

compacted fill. The ~ will ~enerally experi

ence a volume shrink~_ge of about ,2!: when placed as fill,

while the d~'.!;..q~t areas are expected

:i,us.r§;a~e of from ~'.z..-!2.2Z- under similar

to show a V.Q.lum,e •

conditions. The

net overall effect should result in a very near balance

of earth guan.~i~.i~·

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Excavation to depths of the anticipated grades can be

accomplished in nearly all areas of the property wJJJ.i

out the need for blasting. Ripping with conventional -.~ ......... ,. ~-------

equipment should allow excavation in all areas, ejtcept

p:rhaps the deeper cut areas in ZJID.W.. ~nd some of the

limest2ne .• r9,s,~ in Zone III. The latter is usually suf

ficiently fractured to allow breakage into l~t&...~&S.'ls§

and boulders.

5.22 Drainage

Drainage, both subsurface and surface, is vital to the

proper development of the property. Subdrains 1111.lSt be

provided beneath all fills occupying the major canyons

~nd drainage_~,:wale~, even though water is not evident

at the time of construction. It may also become neces

sary to provide subdrains b~eat;h s~-_tlope.JJ,.lJ.s, f,J,

during construction, they are deemed p,~CM$.<l,1;,Y,. :RY the

§£!.1.An&.1-n~. The "Si.tbdrain Layout," ~ij_~

which is enclosed in the pocket at the end of this re

port, shows both the existing subdrainage facilities

installed under our direction through October 1964, and

the remainit.l_g recommendruL!!~l!l?.!!i.;&mll for those portions

of the property yet ur1cdeveloped. Included in the

"Recommended Grading Specifications," in Appendix Care


specifications for subdrain installation, which have ~------· .

been used for all subdrain work to date and which are

to be used. for all future work.~.

It should be understood that the proposed future sub

drains shown on Figure No. 4; are to be used as a gen

eral guide, and that additional facilities may be re

quired as grading operations expose appropriate condi

tions. The ~~s.t,,..12,9!,Sj,g.I]., pattern, and extent of sub

drainage facilities are to be ~;in~.19z the §pj.J.

Enginee;r.at the time of construction. - - ~ . ~-·':l"r.:~,~~~

In addition to subdrains beneath fills, other subsur

face drainage facilities may be required in cut areas

exposing seepage or spring activity. Such facilities

may be in the form of French Drains on, or at the F?-£

of, c;:uts; subdrains incorporated into \lnd~,i_un~

utility trench~s in cut areas;'or hg..;j,~a].lx..,,sb::~

hJ!;.~ug~;! in areas where dewatering is necessary.

The installation of such facilities would be at the

recomm~..w;la~~2P an4 U¥~~ the di~ectio~ the .~:hl

Engineer. """•\ •. ,,,,~•"""<'O''~•·

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Con.tro]. of surface mn.s:!.fJ. is important in the develop

ment of hillside properties, particularly where the

~<?,_!].s aE.s.as e~~~~ as .those at the Westborough Pro

perty. In addition to 4,;al~&~~~.! on constructed

slopes, which are discussed in the following Subsection,

it is recommended that proper facilities be constructed

at the .F~E~ cz.~ ~.2,Sh ~~. and £il;!,,,~s,lo12,.~ so that runoff

does not ~ge freely o,x_~ the en;l?,~,l:l;Q.t::· Simi

larly, individual lots and 2.1di\<l;:\:-P.S s~.t~ should be ' .

graded so that positive di;§4J.i.\&!il .~ fJ;,QJll the ~-

~1:1res is provided ,MJ;l so that water is diverted ~!:!l.

~rom the t.2f_S of emb.1t!ll!tP.!1!!.!al .

5. 23 Slope Stability ···

The construction of stable slopes, both cut slopes and

fill banks, is another vital factor in the development

of hillside property. Factors to be considered in the

design of safe slopes include the strength of the ma

terials comprising the embankment, whether it be cut or •'

fill; the structural relationship of any planar features

in the natural rock, such as joints, faults or bedding

planes along which zones of weakness may occur; the pre

sence of weak soil zones, such as serpentine clay bodies;

31 (

File No, E2204-Ml 30 November 1964

the affect of ground w~r activity; and the affect of

seismic forces.

General recommendations for slope gradients as presented

in the 1960Soil Report were as follows: Cut and fill

slopes up to a max.imum vertical he.ight of 50 feet were

to be constructed at gradients of 1.5:1 (horizontal to

vertical) and 2:1 (horizontal to vertical), respectively.

For slopes having vertical heights greater than 50 feet,

the lower_p,o;t;l..Dns of the embankments were to be flat

tened to W (horizontal to vertical) for cuts and 2.5:1

(horizontal to vertical) .for f~. DE'ainag~~, with '

conci:ete l..:i,_TI~.SL.ru!-.Sft~, were recommended at vertical in

tervals of 25 feet' for both cases. It was further rec-

onunended that all exposed slopes be protected as soon as

practicable with a ~P..XQO.t;..e1:t.fil:aS! or other satisfac

tory erosion control planting.

Subseguj!.nt to the issuance of the 1960 report, devia-- ---~g.ns from the foregoing recommendations have been al

lowed in certain cases where specific study of a given

slope has been made. None of these deviations .has al

lowed cut slopes to be steeper than 1.5:1 nor fill slopes

to be steeper than 2: 1. Some have allowed variations in ' --

the spaci~_of ~' while others have resulted in a

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flatter slop~ than was originally recommended because

of conditions revealed in the more detailed and speci

fic investigations and studies. Recommendations for

specific cases are discussed in detail in Subsection

5.44.

The recommended slope gradients given in this report,

both in the above paragraphs and in those of Subsection

5.44, are based on the strength characteristics of the

materials under conditions of normal moisture content

that would result. from rainwater falling directly on

the slope, but do not take into account the additional ~,.~......._.__--..-~ ......... ~··--

activating forces applied by s;epage from spring or

ground water activity. Therefore, in o'rder to maintain

stable slopes at the recommended gradients, it is J,m:

perative that the seepage forces and accompanying hy

drostatic pressures be relieved by aJ!~guate dr.aipJ!~.

Such drainage facilities may include gravel blankets,

r.2_ck-fillcd surface trenches, or horizontally drilled

~li!JJl,3 (hydraugers).

If, during the construction of cut slqpes, w~ak zones

or adversely oriented p!!_nes oJ WE!..~J.9Jg§l.§ are exposed, it

may become necessary to s_9!);ii~ the slope involved EY. either d~!l.&.e, or over-excavation followed by the con-


struction of a buttress fill. A suitable method of.

stabilization will be recommended by the Soil.Engineer

in the event any such conditions are discovered.

5.24 Residential Construction

One or two-story residential structures may be built -.,.....

either on pads cut into firm natural ground or con

structed with. compa_£!:.ed fill in accordance with the

requirements of.this report. This does not limit the

property to the use. of one- or two-story residential

structures, but the following criteria are for those

structures· ~n;ty. F~.!.~~s:i,_gµ. crite?;,1,L,f,.21 o~

type structures should be given by the Soil Engineer

only after specif,&: con..!.t-d.!ra~ion of the building type

to be used at a particular location.

Only material from Zone I and Zone III will comprise

the foundation soils upon which structures will bear

since the Zone II soils will ng,t be e:&lQa.e.t;l at the

surface after grading. Neither Zone I materials nor

Zone III materials will restrict the use of any parti-----cular foundation type, thus any of the current c~nven

tional f~~g_,J:;~s are as.5§11!.!;.?~ble. It is antici

pated that shallow spread footings, using both contin-

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File No. E2204~Ml 30 November 1964; -

µous perimeter a_!!...d is9J,SJJ;~d in~J'~tqL._fqoti,.~gs will be

used for the majority of the residential construction

at Westborough. The following recommendations are

limited, therefore, to that type.

Becau~e a majority of the ~ soils are badly ~~.h;

ered ~~d very c!J!Y~.Y'> it is necessary to use somewhat

more restrictive foundation design criteria for struc

tures founded on Zone I soils than for those founded

on the predominant Zone III soils. It i.s expected

that some of the deeper cut areas in Z9n!-t .. will, how

ever, provide excellent bearing soil and rock. These --· can most practically be delineated after grading in

that area has been completed.

Zone I: For spread footings used for the support of --either one- or two-story residential structures founded

on Zone I soils, it is recommended that both the in

terior and exterior footings be placed at a minimum em

~cl!n~~! of 12 inches below the elevation of the graded

pad, whether it be cut or fill. The graded pad eleva-- - -tion is considered to be the finished pad grade befo~~

any lt~skf:llling ag_~t the e.~t-~uor of the foundations.

It is suggested that at lea;s 4_t!!£.~S of ~Ring back~

fill be placed against the 'outside of the perimeter ---· ....

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footing to allow proper drainage away from the house. _,...,_..._,,._-....,.. - ----~

For footings placed at the above recommended depth,

and having a·12-inch mini.ml.Dll width, the safe allowable

bearing capacity of Zone I soils is 2,100 p.s.f. for -combined ~ plus. r~al live loading. That value may

be increased by one-third for the added affect of

short-term seismic loading. It is recommended that

at least~ 1/2-inch diameter bJ!!_of reinforcing steel

be used in continuous footin.&§ set in Zone I soils.

For £S!!1Cretf,!. sl.abs-on-&!'A!!L including driveway, garage

and living area slabs, founded on Zone I soils, it is

recommended that a 4- inch lay.er of cr~~J!J::9,£!s be

placed beneath the slabs.

Zone Ill: On Zone II!. soils spread footings for one

or two-story residences may be founded at a minimum

embedment depth of 8 inc;;hea,·measured from the-graded

pad elevation before any backfilling against the

footings. F.mbedment depths given in ~his r~port are

considered·to_be c;Jepths of minimum trenching. into.pads

either £_Ut int~ firm _natural ·ground 2F filled With

pro~~_;-lz_s~acted soJ:1~ For footings placed at the ;

above recommended depth, and founded on Zone III soils,

the safe allowable bearing capacity is 2,700 p.s.f. for -·-

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combined ~ plus real live loading. This value may

also be i~a..al'l.d. (!!J..~_-tb.ix_d for combined dead, live

and seismic loading. The use of a rock base beneath -·----concrete slabs-on-grade in areas of Zone III soils is

considered optional, e~s~,eE in the case of sJabs in

l~..:y-~~&...~~~s, where a 4-inch thick gravel p.A§_e is def

initely recommended, .A guide specif:!,.cation for rock

base is included in Appendix .£.of this report.

5.25 Metal Conduits

The results of corrosivity tests indicate that .little

trouble should be experienced from the S9J;:rosi:2_n of

buried metal conduits provided that:

a) Materials of good quality are used in fabriaction;

and

b) dissimilar unprotected metals, e. g. cast-iron

and steel, are n~ u~ :!,_~,close proximity, to each other.

Except in certain instances, and as directed by the Soil

Engineer, the ~~ated metal piee used for subdrain

purposes need not be asehalt dipped . ... ,., .• _..,,...,! ,T, ............ ,~ ... ....,,._,_,:,0.,_ ................

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1IHl•l1~ I I 11111 ~1111

5.3 Results of Specific Studies (1960)

II ' 111 lli~lllil1 l I I I wl"I I I I 11 I~>

5.31 Apartment Site at Oakmont Drive and Westborough

Boulevard

In the course of the 1960 investigation, it became

apparent., that the natural slgp,e occupying the westerly

~e of the main canyon in the area of Grids _! and 10,

1 and ~· contained numerous areas of instability. This

area is now designated as a propos~,S AJ>_~~n~ Si~~.

~Q_un.ded on the west and northwest .Qy W~ugh Boule

~ and on the east by residential property fronting

on Oakmont Drive. Some of the areas of slope insta

bility have ~ow, been eliminated by the construction of

a deep, compacted fill placed in the canyon and span

ning from side to side up to approximately elevation

~ against the westerly slope. Zones of instability

still exist ~e that elevation on the westerly slope

and some have been covered by thin hillside fills, tem

porarily placed for the purpose of access.

Recommendations presented in "the 1960 report for treat

ment of that general slope area occupying the w~!iJ;;.erly

eg_rtion of the proposed ~artme~~te and underlying the

easterJy (unimproved) portion of Wes.tbgQJ,!&h-~q__ul~d __ ,_ ..... ~~-- . ~

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called for removal of materials f;;gm the s_lope face

and reconstruction in the following manner:

a) Excavate so that a k~ 4~ is formed at

the b~e of the slope. The exposed face should be

cut at a slope of 1-1/2:1 (horizontal to vertical).

b) The base key should be graded backward into the

slope at a grade of 2%, and a subdrain laid at the - --back of the key, draining to the nearest controlled -outlet.

c) A blanket of compacted fJ];!:er _fil".!,~l, f...!~$

thick, should be placed on the key, and then com

pacted fill constructed until the finished slQ[!e is

created at a gradient of 2:1 (horizontal to vertical), - '

with a 2-foot thick blanket of fiJJ;.er ro~k being placed

b.~J;~n the fill a.,u.d the l.:::;!./_Z-i_Lgut facli!,

d) Zone III type soil is recommended for construction

of the fill, with the excavated s l~ee niat~r~~]. being

removed and used elsewhere in a less critical location. ~-

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5.32 The Major Trough {Zone II)

The following recommendations were submitted in the

1960 report which pertain to grading and_ site pre

paration requirements in the Major Trough, defined as

;pne liort_Figure No. 3 of this report.

a) Water wells should either be backfilled with -filter gravel ~ be plugged with a C.Qricrete cap at

least 3 feet thick and of a diameter 2 feet greater -.........- . ' -........._...~,......----

than the diameter of the well. In the former case, a

subdrain lateral should be laid adjacent to the well. --b) Particular care must be taken in placing fill where

the water main of the North Coast County Water District

c.;:9§ .. !'!,g,S the c~n at its soutQ.e:i;:ly end. Adjacent fills

must be extensively keyed int.o_fii;:m ground, _and fill must -not be glas:,.e.Q. o~ the Pi,e.e ~ithout thoroughly h~ plac

ing and compacting fill b_!!low, around, s.n.dJbove the pipe

to a height of not less than 10 feet.

c) In the southern portion of the trough (Grids 7-t,

a..:1 and 9-I) there are exten§.-;j,ye dep.g.j1.i.t;.s. of saturated - !

c!i!Y~ which, at the time. of our field investigation,

were covered with a few inches of water. Stabilization of

this area is recommended by the installation of a herring-

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bone pattern of subdrains followed by placement of com

pacted fill. Individual s~~d~ will be needed to

connect with observed w~ter see.ill\~· Under the weight

of the fill, settlement;;Jtill occur as the clays compress

and water is drained from them. Time will permit, in

this instance, .all s~ttlements to occur-before residen

tial construction is commenced, since fill will be

placed in this area in 1960 and residential construction

is not anticipated in the fill areas for at least one·

year.

d) In the northern portion of the trough, depths of up

to 26 feet of peat exist in the ponds. These ponds

must first be drained of water, then all peat removed

before any fill is placed. A subdrain installation will

be of no avail for stabilization'here, as settlement of

the peat would be measured in feet if subjected to the

weight of fill overburden. It will, in fact, be impos

sible to place a properly compacted fill on such a foun

dation. soil. Subdraips will still ~eedeg in these

localities to tap the springs which feed the ponds. It

should be noted that the sooner these ponds can be -drained the more advantageous it will be, as even a small

decrease in the moisture content of the peat will result

41 y


in a large decrease of its ~olume, and will provide

fewer problems if it is placed in other fills as sug

gested in Sub-Section 5.2. -5.33 Drainage Swales in Zone III

The following recommendatioqs, as they appeared in the

1960 report, are to be applied in the treatment of the

swale areas in Zone III.

a) All t:._opsoil and or&!!!Jf! •. J:l1'.l!~~~J,!"-J should be stripped

f:;.gm the S)!~;I,es, P.!!E!=.!.£~_i;:,:ty i:t.t the l~s.§.t;.:i,Q!t .. 9.J: bas~

keys for fills. The ~ey area should then be cut as in

normal preparation of keys. When the key has been cut

into firm natural ground, the Soil Eq_gJ!l~ .. l!;_r must ~nspect -the site and determine whether additional depth is neces

sary and if the material in the key has adequate strength

to support the fill.

b) In several of the drainage channels there are exten

sive deposits of loose, saturated soil with varying a-..

mounts of organic matter. This soil must be completely

removed from the area of the key, and for sufficient -----distance below_th.~.Js_ey to give adequate protection to it.

This distance will be determined by the Soil Engineer

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when the key has been cut. A s_ubdrain system must be

provided in the key area to insure thdt the soil sup

porting the toe of the fill does not become saturated.

c) The saturated material from the key cuts can bEL_

used in the fill after drying. Most of this soil is ______... -·· -quite granular and is little different from the soil

in the adjoining borrow areas.

5.34 Treatment of Limestone Deposits

The lJmestone rock encountered in localized areas of

Zone III should rip readily during the grading opera-

tions, except perhaps in trenching for u~gerground

u£Uit;.ies, where ~r blast in$ ~he nl;!,c.es.s.ax:y. :.!

The 1960 report contained the following recommenda

tions for treabnent of the limestone rock in grading

and site development:

a) The rock extracted from general excavation may be

used in compacted fill providing it is broken to a .. -maximum particle size of about 2 feet in diameter.

Rocks should not be placed clo5e~ than 5 feet from the

final s~~ of the fill and they should ~ be so

43 v


clustered that voids will develop between rock parti

cles. Rocks 13J:ger than 2 feet in diameter may be

allowed in the fill, but only ll;l?on wri..U,en aP,pr~~l

of the Soil Engineer.

b) In areas where the rock will be exposed at foun

dation level, it should be 1:!Ildercut to a depth of at

least 2 feet and then brought to grade with compacted

fill of material relati~ely free from rock.

c) Cut and fill slopes should be constructed in ac

cordance with the general recommendations of Subsec

tion 5.23. Where the dip of .the slope is to be near

that of the limestone beds, the final gr~e m~~

~ontrqll~d bJ th~k diJ?. at the discretion of the

Soil ~!lgineex;.

5.4 Results of Specific Studies (Post 1960)

5.41 Introduction

Following issuan'ce of the 1960 report, it became

necessary to make several specific studies with res

pect to soil and geologic conditions within·. the West

borough property. Some of these studies were necessary

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for execution and completion of projects then underway, .

others were to provide the necessary information and

recommendations for anticipated projects, most of which

were of a greater magnitude than anticipated prior to

1960. The following paragraphs present the results and '

recommendations culminating from the special investiga

tions described in Sub-Section 2.4 and some other re-

quired studies .

It should be noted that the followi!!lL.recomm~J:is,ms

supercede those made in 196Q, which have been restated

in the foregoing paragraphs. In the event any of the

following.recommendations are in conflict with those

presented in the 1960 report, the more recent will pre

vail.

5.42. Apartment Site at Oakmont Drive and Westborough

Boulevard

From the investigation conducted in July 1963 and des

cribed in Subsection 2.41, it was concluded that the

then proposed apartment development was feas.ible, but

that, in.order to provide proper stability to the

westerly slope and its ·proposed terraced foundation pads,

45 "'

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an extensive stabilization program would have to be

employed. The measures recommended called for the re-.._

m™l of ~oil and ;i;:2ck f!.£!!1 the e:i_sisti~ slope face,

followed by reconstruction of a drained, b~ttress. fill

embankment, the configuration of which resulted in

multi-level terraces for building sites. Details of . .

the recommended slope reconstruction, including cross-

sections, were presented in a report to Westborough ' Homes, dated July 1963, identified by File No. Ell52-ML -- '.

5.43 Proposed Storage Reservoir Sites

The proposed resermir sit£. explored by Borings No. 50,

51 and 52 of the 1960 investigation was found to be

suitable under topographic conditions that then existed.

A ~parate :r;:~PS!tl of that investigation was issued to

Caesar Callan Homes, Inc. in !2§JLunder File No. Tll85-l.

The above site was never utilized and in 1963 several

other nearby sites were explored for the same purpose. - -

These were at a lower elevation by virtue of excavation

in the area. Future plans at the time called for exten

sive excavation beyond the-proposed tank, leaving it on

an excavated bench or terrace. Because adverse rock

conditions· .were fouqd by the explorations, and because

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of the topographic orientation of the proposed reser-,,

voir, suitable sit~s were not ay_ailable in that par

ticular. area of the property.

5.44 Slope Studies

Unit 4: In September 196_.l, it was requested by Mr.

Dwight Phillips that a slope analysis be made to de

termine the safe gradient at which ~. m~ ~

bankments could be built in Unit No. 4. One of the

fill embankments was proposed to a maximum vertical

height of 200 feet, the other .. to a maximum vertical

height of 100 feet. The two fill embankments may be

identified as the major fill areas on a drawing en

titled "Intermediate Grade Plan-Apartment Ar.ea South

of Unit 3, Westborough, San Mateo County, California,"

by Theodore v. Tronoff, Drawing No. C-G-43, d~ted July

2, 1963. The proposed 200-foot high embankment· is the

one shown easterly of the inters'ection of Shannon ·Drive

and Limerick Boulevard in Unit 3, and the ),,QO-foot high

slope is the one at the 3.Ql!th~asterly property corner,

~-~1?,S~Rt;;_t;p the R.0JlJ;qgw.Q9d Subdivision. This area has

since been designated Vntt ~Q. 4 of Westborough on

drawings by Wilsey, Ham and Blair. As of -this date,

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the 200-foot high fill is op.ly partially complete,

while the 100-foot high fill is to grade.

After a series of additional tests was performed to

confirm the properties of the soil being plac~d as

fill, thorough analyses were made to determine the

maximum gradient at which the embankments could be • ..

built to their proposed heights and still offer ade

quate-·factors of sa_:fety against embankment failure.

through massive sliding. On the basis of computer

studies Which included the affect of strong earth

quake forces, the following recommendations were pre

sented to Mr. Phillips on 14 October 1963: ---Fill A {200-foot high embankment) __ . ..........,.._....,-, --~ ....... ·~ ,,

No steeper than 4.5:1 (horizontal to vertical) from

top to toe, including bencb,g_s.

' .. No steeper than 2.4:1 (horizontal to vertical) on

any portion b~~i;~a.

Ten-foot wid~, ~i,ne.d d,!!!n_.!!:~ should be spaced

at maximum vertical intervals not to 'exceed 50 feet.

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FILL B (100-foot high embankment)


No steeper than 2.3:1 (horizontal to vertical) from

top to toe , i::;no.::c:.:lo.:u;.:d:;:i:;;;n;:J;g~b:..:e~n::.;c:.:.h.=~

No steeper than ~(horizontal to vertical) on any

portion between benches.

Ten-foot wide, lined drainage b~ should be spaced

at maximum vertical intervals not to exceed '±.9 feet.

The above recommendations have been followed for work

done to date in Unit No. 4 and should continue to be

followed for all future work. They are, of course,

dependent on the continued use of Zone III soils for

construction of the fill. Any change in material will

require further analysis.

West Park 1 and 2: From the special investigation of

the westerly portion of the West Park Subdivision, des-,-cribed in Subsection 2.43, it was learned that the soil

and rock conditions beneath the area of proposed deep

cut possessed certain weaknesses. The ~ck. was badly

!E§tctured and altered due to repeated sheahing and

,i;;_rushin_g from movement along the nearby San Andreas.

fault. Zones of wet cl.!!¥ were found within the softene.d,

File No. E2204-Ml _ ' -30 November 1964 ' ·

'

~?ck, and in many localities ground water was present.

The natural conditions, when analyzed for their slope

stability, taking into account strong earthquake forces,

led to the following recommendations -for construction

of a cut slope illllllediately easterly of Skyline Boulevard:

1. Cut the ~pper portiQn of the slope at a gradient

no steeper than 1.75;1 (horizontal to vertical). The

vertical height of the upper portion should not exceed

30 feet. An ~~ption to the foregoing is about 200

lineal feet of slope at the property line in Grid 8-K

where a pre-existing cut· at !.:11.!. at a height of ap

proximately _10 feet may remain. Below that pre-existing

cut, the recominendations as contained herein are to be

followed.

2. Provide ~0-fo~j,ge, Jj,.ne!l d!ainage benches at

vertical intervals not to exceed 30 feet.

3. Cut all remaining portions of the slope (below

the upper slope bench) at a gradient no steeper than

2;1 (horizontal to vertical). -4. Provide a £-2!1£!:~.t..~--l.:!.n.~~-4;:.~iP-ag~_fil.t.9.P above the

t()p _ _g_f __ qµt along its ~tiE_t!~!-~~1!:

File No. E2204-Ml .30 November 1964

5. Where the high pressure gas main lies within, and

immediately adjacent to, the westerly property line

(in Grids 2-J·through 5-J) the;~ of cut should begin

at l@ast.! feet easterly '!i the centerline of the gas

~ai]:t, unless of course easement restrictions require

greater offset. A1so, along this same portion of slope,

the lined ditch at the top of the slope should be placed

~~erly of j:he g~_).i:t}~_t:r,_e,~h.

6. Collect drainage from the culvert passing~~~r

Skyline and discharging onto the Westborough property ··-·~--··-~·

at approximately G~.5-K and lead it into the slope

drainage facilities.

7. Install horizontally-drilled !ry_draug~ in the cut

i;i].o~ to relieve seepage and spring activi_ty as directed

by the Soil Engineer.

Unit 3: The conditions encountered in the completed cut

slopes of Unit No. 3 were found to be favorable from the

investigation described in Subsection 2.44. Adversely

dipping clay or ~j._l,,,t:y_tlay :J,,~yers within the Merced sands

were suspected in the area, so additional borings were

called for. Very stiff clay ilnd. silt was found in some ~- ___ ............, ___ _

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of the recent borings, namely Nos. 72, 74 and 75, but

their attitude was considered favorable, posing 9Q..

apparent _threat to slope stability. No ·corrective or -............-~~~--~-~-,~-·-~·~-

stabilizing recomroendations were given for the slope

in Unit No. 3.

5.45 Sag Ponds-in Zone II

The results of the recent, additional borings made in

and around the no_~pond in Zone II defined

the depths and areal extent of the soft organic material

in the pond. The borings revealed degosits of peat to

an-elevation as loW as 595, indicating the maximum depth

to which excavation of the organic material was to be

made. -~emoval of the · yns.uitabl.e_watetial.s has now been

completed under direction of the Soil Engineer. -·-- .......... _........,. __ 5.46 Street Pavements

Since 1960 various minor studies have been made for the

purpose of determining t;~5al pavement desigp. thic!s

~~~s for ~sidentia~ street;.~ built on subgrades of

typical soils in Westborough. From numerous Resistance

Value tests performed on both Zone I and Zone III ma

terials, it has been found that the we~red clayeyEock_

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of ~g__l. possesses R-Values ranging from 8 to 23. No

doubt local areas exist where better quality materials

may be found in Zone I. The silty sandG of Zone III ···~-~· ···-·-·---

consistently possess R-Values of 37 to 43, with a typi

cal representative ay_ei::_~g~. of ~.Q.~. It is shown then,

that except for perhaps some local areas of hard rock

in Zone I, the materials of Zone III provide better . .-....,................__,_..........,,.. __ subgrade soils for sj:..r~ construction. ~'-----

Using the most current Sta_t.e cl!?s_ign_procedure (State of

California Test Method 301-F, 1964) the following t;y_p_i

~l pavem~E!=~Sti!?,Il,§ are shown for average subgrade

soils of both Zone I and Zone III. It must be noted

that the following sections are based on generalized

subgrade R-Values for various traffic indices, and that ~-- ·-------"""'"--... ~

the conditions for any particular street must be verified

by additional testing and design. The following tabula-'

tion may prove useful, however, for prelilllinary d~~

and estimating purposes.

53'


TABLE .II

Generalized Requirements for Street· Pavement. Design

Location Zone I - Average R • lS

Design R-Value lS lS

Traffic Index 4 s Gravel Equivalent 13 16.5

Alternate Sections 1A lB 2A 2B -P. M. s. 2 2 2 2

Class II Base, R= 78 rnin. '

8 10.S

Class "A" c. T. B.

Class "B" c. T. B •. 6 8

Location Zone .lII - Average R = 40

DesignR-Value 40 40

Traffic Index 4 s --Gravel Equivalent 9.5 11.S

Alternate Sections 4A 4B SA SB

P. M. s. 2 2 2 2 -Class II Base, R .. 78 min. 4.S 6

Class "A" c. T. B.

Class 11B tt c. T. B. 4 4.5

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15 r 6~5

21.5 r 3A 3B

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14

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lS I 6A ·6B

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5.47 Settlement Analyses


Subsequent to the studies made for the 1960 report,

additional consolidation tests have been made. The

purpose of these additional tests was to confirm

earlier conclusions on the basis of different, and

perhaps more representative test methods. The more

recent tests were made to study the settlement char-...... _.,.._, __ acteristics of the typical Zone III soil when placed ,,~,-_....,--.-~•-....,o...-... • •··•·••••~rn.-............ • .. , •

as f:.!.LL· Their results represent then, the behavior'

of the fill itself and not the materials on which the

fills are placed. The behavior of the latter has al

ready been well established as discussed in Subsec

tion 5.32.

Except for the more recent special tests, consolida

tion data for this project have been obtained from

standard one-dimension consolidation tests, using 1. 90-'

inch diameter sample rings in which the samples are

0.80 inches high. Recent tests, made to give compara

tive results, included two consolidation tes'ts on 1. 90-

inch diameter samples and one test on an 8-inch diameter

sample, having a height of 3 inches. The latter test

utilized the Bureau of Reclamation 8-inch mold and was

performed in accordance with their test designation E-13.

55 '(

:Vile-No. E2204-Ml 30 November 1964

All these tests were performed on a well-m~ed, split

sample of Zorie 111 soil, typical of the majority of

fill material placed at Westborough. Each of the test

specimens was· compacted to .2!& rel~tive cQmpactiQp, at

the optimum moisturi;:_ content, based on the ASTM Compac

tion Test Dl557-58T, Method A. Descriptions of loading

increments, moisture conditions, etc. , for each of the

tests are noted on f_~A~~.s No. !Q. th!~~~h !~, which

graphically illustrate the consoilidation test results.

The Bureau of Reclamation test also provided direct

data pertaining to permeability of the compacted sample.

As shown on the figures illustrating the consolidation

test data, the Ufil~.;::.!!!O.~-l;l~!ll!'IR~ r.§.tes for each of the

test specimens is ns_~ly ~'Pl!l!.~~e. Thus, consolidation

of the fill material takes place nearly as rapidly as

each additional increment of fill is placed on i~. The

net effect is, that at or shortly after completion of

the fill placement, additional settlements within the ; ..... ,,_~., ......... -~~--~~ .. '""""--~""""""""......--...u:-•~ .. fill are expected to be ~~significant.·

Similarly, settlements of the fill under highly concen

trated loads of significant magnitude, such as those im

posed by ~~~~t;..t.!?i!:§ of structu:i:-es larger than single-

,/ 56

•


family residences, are expected to£££_~ almost immedi~

atelr/ They are, however, calculable and can be deter

mined for any given structure once its load distribution

is known.

5.48 Seismic Hazard

It must be recognized that, as with any development in

the San Francisco Bay Area, there exists a certain de

gree of risk with respect to potential damage from

e~~hg~ak~~· To completely avoid any such risk would

eliminate development in nearly all of California,

particularly the Bay Area. Social and economic factors

apparently prevent the latter, It becomes vital, there

fore, that the hazards of de:y;~lopmen.t be made.known, and

that, if possible, they be e-2~ so that compensation

may be made in de,sign. Unfortunately, a quantitative

evaluation of earthquake hazard depends upon so many y~

AJ;!.l~s and, in fact, many unkl;i.QWO.S., that any evaluation of

potential hazard becomes a pro_gnosis based on the pas~

9_.ehav.io;:- of the ground !i!nd stru~_E.~S during r_ecgntly ~~

-;:_g;:~~d E!!3!.;JiqH.!.'154il activity.


In an effort to make a proper evaluation of earthquake

hazard at the Westborough project, and particularly

within the proposed West Pa;_k Development because of

its ~~ID. to an ~EJ; __ i:v.e ~l!;, a special report has

been prepared for this office by Dr. Frank W. ~~.

Consulting Geologist. His' report, entitled "Earthquake

Hazard at the Proposed Site of West Park Units 1 and 2,

Westborough, 11 is :(,nc!_udg_d as Appendix D of this report.

After careful evaluation of Dr. Atchley's report, and

after lengthy consideration of the earthquake question,

our conclusions are basically the same as those described

by Dr. Atchley; namely, that the main line of movement of

the San Andreas fault does pass thr()ugh the Westborough ,.,,, ·-~~--...,..-~·-· ....... .,.......... .... ~. ,.~~ ····-· _ .. , ...... ~ , .. · ... :-• -. ,• ••, ,..... . ... ......_:·~ ·,,:,.:::~·.;;".,,....

property (coincidental with the area defined as Zone II

on-Figure No. 3); that earthquakes may be expected as a ------~--

result_ of stress relief focused at some depth below the

line of this fault at some time in the future (these may

or may not be accompanied with displacement at the ground -~ ........ --

surface as occurred in l~J'.!6); and that the area within the

estimated limits of possible surface rupture possesses in

herent ~jlrt~uake.-haza:rd that approaches the l!l~X~~ not

withstanding the fact that other areas within the San

Francisco Bay Area are being developed which may possess

equal or greater earthquake hazard. -

•

I· I

' I '•


We ggru;;.u:i- with Dr. Atchley's recommendation for devel

opment of West Park Units 1 and 2 that "final project

planning of struct~e orient"1_~ arrangement and ~

s~~~ be certified by a,Structw::.al.J:Jl_~~~ with recog

nized eminent stature in earthquake design." In addi

tion, we suggest that strong consideration be given to

the possibility of allowing studies to be conducted

along the fault within the Westborough property. There

is much to be learned about earthquake activity and

ground response, which can be used to continually im

prove structural design, and perhaps someday even pre

dict earthquakes. There is presently a strong interest

among Seismologists and Structural Engineers from educa

tional institutions, governmental agencies, and private

practice to undertake such studies. Certainly a, pro

gressive scientific attitude toward earthquake hazard

is to recognize the existence of the hazard and make

every effort possible to learn as much about the causes

of damage, so that through the application of advanced

technology future damage, and thence future hazard, can

be reduced. Specific studies from which more knowledge

of earthquakes may be gained might include detailed,

periodic surveying along the fault zone to detect ~~~g~ --- ---~_....~..._~

movements; and the installation of highly specialized ~--~~...........,...

59.,,/


instruments to measure ground motion and stress changes

within the earth's crust.

As a final recommendation, it 'is suggested that prospec-··-...... _______ ,~-···~-,.-.·~ tive eurchaser§ of property within Westborough be ~

aware of the existence of th~ reP.Q:i:.t. '·· ·--~ ---- .

5.5 Limitations and Uniformity of Conditions

The recOPllllendations of this report are based upon the as

sumption that the soil conditions do not deviate from those

disclosed in the borings. ll any variations or Qi:J_q!;!§j,_!al:~Je

£'!_1.!9.!.~:!,.o.ns are encountered d~tyL£.onstr4~_gg, or if the

proposed construction will differ from that planned at the

present time, Gribaldo, Jacobs, Jones and Associates should

be Q.Otifi&Jj so that s_upplemental 'r,e,cm,nmendations can be given. -~---·~--

This report is issued with the understanding that it is the

r.ft~P~ of the owneri or of his representative, to

ensure that .. the information and recommendations cont:l'!ined

herein are called to the at_ten.tl-9-B of the At:chiJ:ect and ~&i

~~~ for the project and i.~~2.E_porat~ into the J?la3\'!_, and

that the necessary steps are taken to see that the ~ontractors -......... .............. _ __.........--

and Subcontractors <;'_{lrry __ ~!!l;. such i::e_t;,Qlll1'.ll~!:~-~J._q_ns in the field.

"

r

Appendi.x A

Laboratory Test Results

[

~

~· t ~:·

l f [ '

. l ~

t ' TI ··~ f

'f

r '

I I

• ;,

l

I I l

i I

I I

~.

J '!-:".

l

' ii ~

I - . 4

1. 1-" -.. -· • l J ~·.

" -.;,


TABLE III

Summary of Moisture Content, Dry Density and Shear Test Results

Hole and Depth Dry Moisture Angle of Unit Sample Density Content Internal Cohesion

Friction No. ft. p.c.f. % dry wt. degrees p.s.f.

1-1 1 77.2 29.5 28 700 1-2 12 69.0 53.0

2-1 1 88.0 22.4 2-2 6 93. 5 31.4

3-1 12 111.6 14.2

8-1 12 112.7 11.4

10-1 17 96. 6 25.6

14-1 1 77.6 19 .8 25 310 14-2 7 108.2 15.3 26 700 14-3 12 109.8 18.8

15-1 1 73.4 23 .2

16-1 7 109.l 13.9 24 790

27-1 18 18.7 275.0

34-2 17 109.3 15.0 37 480

63

1;'1

!I :11

I

i;

I l

r· i ~ ! ] ' n • f

l! l I

l I '

File.No. E2204-Ml 30 November 1964

TABLE III (Continued)


Hole and Depth Dry Moisture Angle of Unit Sample Density Content Internal Cohesion


36-2 7 106.3 17.7 20 620

37-2 12 105.7 19 .9 32 160 .

38-1 2 107.2 16.5 24 660

39-2 12 104.8 17.5 30 575

42-1 7 109.6 11.5 27 860

53-1 1 118.0 18.9 53-2 8 112.8 25.0 53-3 13 129.8 16.1

54-1 3 109.2 17.2

54-2 8 117.2 20.1

55-1 1 81.8 44.5 55-2 3 93.8 36.4

55-3 8 92.0 38.9

55-4 13 128.5 13.5

72-1 1 98.9 12.4

64

; '

l . t .,

f· '··

r L

i~ l..:o,~

"\

' -~:.

I l •· • • • I

" ' ~ •

~

1 •

! File No. E2204-Ml 30 November 1964

TABLE III (Concluded)


Depth Dry I Moisture Angle of Unit Density Content Internal Cohesion

• ~Hole and Sample


82-1 ,8 121.9 15.3

83-1 8 114.0 17.2

89-1 8 112.l 17.9

65

' ' ~~ '1 \

.·:~

\ ., ', . I

I•.·.· .. ·.'. I ' l ~ ':1 i

I

.. i.·.~ .. 1·:··.·. r


TABLE IV

Summary of Laboratory Compaction and Shear Teat

Sample Number

or Location

D-1

D-2

D-3

D-4

D-5

Hole #3

Hole 1f3

Depth

ft.

2

5

1

8

3

0-8

8-20

Results. on Disturbed Samples

Maximum OptimllDl Unit Dry Mo is cure Cohesion

Density* Content p.c.f. % dry wt. p.s.f.**

111.8 14.6 420

108.7 13.0 780

111.5 12 .2 300

110.2 13.6 480

109.8 13.0 450

115.2 13.5

122.1 11.6

* Based on ASTM Compaction Test Dl557-58T, Method A.

Friction Angle

degrees**

21

18

27

17

27

**Samples remoulded to approximately 90% of Maximum Dry Density •

,,

66

·~.

"' ~·. TABLE V


Summary of Swell Test Results

. ' . l

~

Sample

No.

A

B

c

D

File No. E2204•Ml 30 November 1964

TABLE VI

Summary of Direct Shear Test Results for

Slope Studies ~ Westborough Unit No. 4

Source and Remoulded Moisture Description Density Content

p.c.f.* before test

Fill A - Unit No. 4 100.9 10.9 Brown Silty fine SAND

Fill A - Unit No. 4 100.4 11.6 Light brown Silty fine SAND

Fill B - Unit No. 4 100.6 11.2 Gray-brown Silty fine SAND

Fill B - Unit No. 4 100.2 11.6 Light brown fine SAND .

Silty

* Remoulded to approximately 91% relative compaction.

68

Unit' Cohesion p.s.f.

270

0

460

90

Friction Angle

degrees

30

34

28

33

I

I

I

I

I I . r ' [

E

i I

·~

~-

• I I

~ !

• I

!

TABLE VII


Summary of Laboratory Test Results on Typical Zone III

Fill Material Placed at West Park Units 1 and 2

Sample No. E -Yellow-Brown Fine Sandy SILT

Sand %

40

Gradation

Silt %

50

Maximum Dry Density

p.c.f.*

118.3

Clay %

10

Liquid Limit

27.9

Optimum Moisture Content

% dry wt.

12.4

Coefficient of Permeability cm./sec.

2.4 x lo-8

Plasticity Index

7

Unit Cohesion p.s.f.

690

Specific Gravity

2.69

Friction Angle

degrees - ·

30

Consolidation Data

See Figures No. 10 - 12

Ill * ASTM Compaction Test Dl557-58T, Method A .

• I

,1 69

i I

. I . • r l I

• I . • R

I 70 l

File No. E2204-Ml

30 November 1964

-H-+-i I ]1-1-+:++--l--l-+-H- I -- --1-+-H-+-+-++-+-++ ·.:-+ .. : ; t"·; -~--; r,--_Hr-+-~f:.!=~~::",_-_,--+_,· _--+1--+--+-+--~

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Figure No. 5 - MOISTURE-DENSITY RELATIONSHIP CURVE

71

File No. E2204-Ml

30 November 1964

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Figure No. 6 MOISTURE-DENSITY RELATIONSHIP CURVE

72

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File No. E2204-Ml

30 November 1964

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Figure No. 7 MOISTURE-DENSITY RELATIONSHIP CURVE

13

File No. E2204-Ml

- 30 November 1964

~t:·:t.-·. ·+-+-t ;--+-+-+--+-+-+- 1--·+--l--+-+----H+-+-++· . ....... 1- -1-+---H+-+-+-+-++ ~+--1--++1-++-1-++-t--+-H-+1-++-1-+- .. +-1-+-+-:__,_ , _ _,__.--4----1 -·· ~-- ·+-1-+-+--l-+-+-+-+-·I-+ \ -t--+.--Jl-++-l-+--l--l·-l--l-+--1----11-l--.\--l__j__-i----~-l

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Figure Mo. 8 - MOISTUJlE-DENSITY R.ELATIOHSHIP CUR.VE

74

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.I • ,, I:

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File No. E2204-Ml

30 November 1964

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--1

- ~ ~- --l--l--+--l-U-+--1--1--1-ULJ-J - ·+-+-_,

Figure No. 9 - MOISTURE-DENSITY RELATIONSHIP CURVE

75

l [

' l

I E

; i J I

' '

76 II

~

---

c 1 0 .... .... co v .... ..... 0 -----ti) 2 c 0 u .... c Ql () ,.. Ql 3 p..

0.1

M I 0 ..... >: ti)

145 Ql .c () c \ ....

\ I

'\.' 0-0 c ' ....

'O co Ql

0::

..... co ....

Q 140 0

,, .

·-.~ I ' ~

p p

r--.. _

r---~

·-"-...

.~,

' '\

'\

File No. E2204-Ml

30 November 1964

Sample E Yellow-brown fine

Sandy SILT Ring Diameter: 1. 90 in. Sample Thickness: 0.8 in. Sample Density: 109 p. c. f.

---- ' -- t-. '\

II·- I

-- ..... I\ ,.,___

\

-- -- \ - \ --n

1.0 10 100 Applied Pressure in k.s.f.

(a) Pressure-Consolidation Curve

'

...._

l 2 3 4 /Time in Minutes

(b) Time-Settlement Curve at 2 k.s.f. Load

Figure No. 10 - CONSOLIDATION TEST DATA

77

.

Jr

File No. E2204-Ml

30 November 1964 u ,._

-......_,,_

.......... ..........

1 . " . c "... 0 .. .... "... 'r-. .., <\1 'O .. " ). .... '!>. " ...... 0 '!>. " <I) 2 c '-0 u "' !>.. . .., " ... c Qj .......... 0 ~

3 "' Qj p., -...._,_

4

.

} . _...

' '- .. -, I_

----

If.ii &llll.?

Sample E Yellow-brown fine

Sandy SILT Ring Diameter: 1.90 in. Sample Thickness: 0.8 in. Sample Density:. 109 p.c.f.

.,,....

' - -' -----· - -· - ... ,.

- ·-

"... -.....::::..

...

• •

•

•

• :

i '

0.1 1.0 10 100 [

55

""' I 0 ...... i<

<I) Qj

.J:: <J c \ .... ' I

' 0£) c 60 ....

'O ' '11 Qj ~

r< <\1 ....

Cl

0

Applied Pressure in k.s.f.


-

1 2 3 4

VTime in Minutes

{b) Time-Settlement Curve at 2 k.s.f. Load


[

I

. l

f

I I

I ~· ~· ,

--! I ~ J

~ I .~\

0 c 0 ..... w <ll

i:> ..... r-1

0

"' 1 c 0 u Sa

"" .

c QJ I

u ... QJ 2

p..

0.1

File No. E2204-Ml

30 November 1964

Sample E

Yellow-brown fine Sandy SILT

Ring Diameter: 8.0 in. Sample

0 Thickness: 3.0 in.

~ ~ Sample

_ ...... Density: 109 p. c. f. / ,~ ,...

It a.f.~ ,ura Ce ~

' ~.

1.0 10 100

Applied Pressure in k.s.f.



r..-·--------------·-----••••••••••••••••••••••••••••••••••"iiiiiii"il-ai---ililjjijilli;i~==:i.:sz:;·.~·""ft'll'E'!·:il .. i!:il·ii· l'll:lilifll~?li.ifrb

I

• I

r "

l

'i .' of'Test Boxings

''

··.,,

·-.·

. ·~-.·~····--·-,. '''" --·~---~-

i,·, "'"''" :o,,.,, '·' •

l..;,,c,:

7 7. 2 ?9. 5

_ I

(..9 .o 53.0

I I

:1 I r '

I -------------------------~ -----~~

[,_ '·- '""'T'I<

f ~ ••.

I• 'l•co ...... ---~·~

:i-~'.i •• M1•\•<,•n• Conc•r.: t ••r• ~c. o.c.!.

LOC. OF t~:ST ):10/(ING till. 3 -------+---+---' ·1 I-' !

,_ (;ro~m'(I S~irfl'llC"~ ~ E1~v. 5BO ·f---t=o+-----~--~='---='-"--='----+---+---l

''[1:-j.' ''"""• fina Si1'y SANO, O'Ooer•c.ly fi<m, 1-:,.l1· _,_._0_ 1_•_' ____ , ______ ._

I , I I I. . I 10

I

; I I r

I" ]-1

........

;a 11\0· +1.·f

41 fFi . Jll

Ligh~ brown fin" S"ND, finn, d~rt6t•, mo19f.

tu~Ct.111'11ng Very £' Lrm

l.igtJ[ griiy S11ndy S),l.,T, fi:rw. ml>l!l!:

Brown Sil~y SAND, v~ry fi~m. mot~r

111.i;. 14.l

I ,, • th

I (~----_-L_ _ _,__ ___ ·_o_,_,_._._,_,_,._ •• _._,_._,_._,_,_,_'_;_·;_,~~~~~----_-,~--···--

I ~;-.,.,

.•. I).

I 2-1

I· ' , _

I ,_

I 2-2

· 10·

·15

·17

.... ,,. \, .... ,,." "

File Na. E 2204-MI

30 November 1964

---,---------------.-·---·-J·. •:"+

-··~

'""" LOG OF TEST BOli.ING ~0- 2 . . ~,

··------~~~~-~·-----------l---~----Crmind S\1~f~c"' • Elev. J2:;

: ~T'.' D:·~k--,;~-::;:; S11ndy SILT ~u:;:;-,-,-,·v·-.-1-,----+--,-,-.o-+-,-,-_ -_,--; .. 0 ~ · moderi;itcly fi1"!D., moi11t t:o w~I: ....

•• 0 ·: ~

~:

l'"'.L-:-t,-:-h-,-:-h-,_ c1.,.sw· """ ge.vol, soft, mui~r ro ~~t

Be~umln& m Silty Cl.Fit wtrh l~~aes Of ~nnd, sufc, mo1~t to Wet

L~ght hrown Sandy CW\.Y. ~oft, mQi~t

9J.5 :n,4

-------~~--~~--·~·-~ ---------t---t-·---<

,.,, ~

lo<•""'' u\•

J.mp••

But ing 'f""'rwtr1.sted ~t; LI fe~r

LOG Of TE.ST BO'RlNG NO. 4

Grot111d S1.u:f11ce ~ f.!~v. 512

. ~, .... 11ry >L.:.!n.rt

"""'" T.' ~·<'": ... t o.c l l dry vc.

O·C---+~~t--------------------+---+-·--

J~W::.· _,,_._'_'_'_'_""" ___ ,_._._._,_'_'_"_· _'_'_"_,'_'_· d~y

'

. 20·

· .. ·:: .. :· Light hrown fin~ Silty SAN[), fil;Ill, ;1p "'"", mo lot

lil

-:;i:r :IJt \(.t .111 :m1-1t1 irlr-

" Nt' ·°)f.>·t--;~~+-------------

- ------------------------· ---·---~--~-

Figure Na. 13 -LOGS OF TEST BORINGS NO. l,2,3,and4 .

••

Fite No. E·2204-MI

30 November 1964

. 5

.JQ.

. 20.

'" ,. 1:''

. ~-~ -------LI\ • •:1<t

Cor.cooo l ,,., ''·

------------~, .,.~ .. ~-··· ----

.~. ',", '·' ' ' .

~--- -···· -----· ~~···-~-·~--~------------ I L.. I ·- ---· ,_ ''"'·' ,,,.,,1. \"<•c(~ CH.i<n,c:;,,, .. 1 -.: ~-rt ' ···- ., ••• ;:" . -'·"· I >-+--f--~·---+---'-"'"-' -"-'~T_Es_·r_B_O_RI_N_G_N_o_. -'----L._· - ~- ~ ·, --·"'

Cround Su?;"f.fl<:.if!' • ~;lie\I. 370 L · . 0·>--+-1-11r+-D-.,-,-b-,---,-,-LT-. loo•e, dry ,. ___ ---;I I ! I

·10.

);.

. ?O .

:'l.:J:'l: Li.~~~l'~rmrn, fin~ Stlcy SA~D. firm, I j I i 11_ I 1 .

yly ,._ . ·.+:·.· 11·· 11•·· 1JJ:

,_, ·~1r ir \IT ii'c

. .;~_ ·"· COi'll'llE' .$A!1[l ~n(I fl~~ 1:0 r:itc"dii.;m rounC!i>d CRAVEt, <l~y, <len8e

·,:; ..

"<- ••

·"<' 0 .• ;

' 117.1 j 11.4

I

::>---+-·: __ : __ ,._+_.. ___ -_--___ -.-,~~-.. ="='· --~--,_=~-,_"-.~,_.-,~-·~,~,-,_~_,~.-._,~~~~-_J~i=c Figure No. 14 -LOGS OF TEST BORINGS NO. 5,6,7, and B.

[

(

l [

r [

I ~i.· '•

I ' ,.

I I 1

----+--1--·---L=<_>e=· ~'~"-· TEST BORil'lG NO_.~''-------+-Gtuund S~-~·~ 48">

·----+--urg~nlc Sllty CLAY, Gofc, ~~[

~- W/L f;/19/60

Ltg.ht br~vn Silty SAND, 8ufL Eu ro~dium d~ns~, ~Oi9t to ~~t

----·····-"'···-··-Dark br•JWll Silly CU.Y with 111.ITHl, eoft

to ~~dl1..:111 ~en~~. wet

. T••: .•

•., ~". r< ,."""''' ,,, _,

·""""''-+------·-·'··-··-·-- --~~···--,-+----+----<

. 10

Borf.np; 'l·~·1·~Ln11c~d at 27 f("f'I:

··-----------

LOC OJ.' T~~ll,.1,~G NO. 11

·;o·J-. .,--,--,-"e"'c"c"c"~":C·Surf.ac1111 ~ ~'.lt!V, !do U~rk btawn Silty CLAY, ~uft. moi•t

----. ·-··'·~----l.Lght brown So!l'n~l)' C1.A'i, firm, diF:n"'.!,

1:11oi1t

cr .. y CiiY "'1th 9;;-ii c:RAv~~L. firm. tlen~•, mot•t

,_]J __ _

,.

''"'.,.' -.Jr,,·t.

'"·~I• >.·.

·2U.

0.,1> •·•m>•I" l,, •o

''~~',. ~'m « ',, ·• ~.

;.,. ~ l..>~:c 1,.,

"""rL•

File No. E 2204·-MI

30 November 1964

LOG OF TEST BO!HNC ~HJ _~cl~O'-------<

Cro1.1nd Si_1r fai::~ - Elei.:~ 4~)c5c__ __ _

Dzltk brown Cl111yTS"fL'!', solt, moitt

ll11rk 1.>ro<-'11 o~gani.c SILT, 111.oderacrly fim, ruo11!11::

B~cQm\n~ org111nic Sllty CIJ.Y, med~l.D. ~~~8e. moL~~ to v~t

~():;:; OF T~ST ~ORINC HO. 12

--_____.::._. ~:~.:., .. -~

9(1.ij 2~.6

•• ~~~'! t:->nUM

'' . ! ~ "'' vt.

0 -!---+~~+- Ground Surface ~ .E::l~~-''o•oO'----..f.----1-·~-l

5 •./

· 10·

.:,-.().

D.!'lrk t>~·uwn SILT, 11;10•~, d1·y

D1111rk hr.-...m SU ty CU.Yr •of(,: 1 ti:.O!.•(.

v~ry pl••lic grf'fl'TI CI.A\'. !it"m, 11110111-r ~.o 1-'t-t

(Serptmt.lnl!" (;l.i11y)

beccrotng •1mdy 'IO''l.th i!RI111ll rQck fr&~De[Hli

· 2 I ·f-~·1""'"'1--81;1rlnp, T~~m1n•tr~ •t 21 lee~

(kl!'f(l!l!il.)

Figure No 15 -LOGS OF TEST BORINGS NO, 9,10, 11, and 12.

i .I ,.

" I "

•,>

,i

File No. E 2204-MI

30 November 1964

!r. - •l«+

........ ~ .. ~ry Mo'''" .. """'"' c,,.,..,, LOG 07 TY.ST ~OkittC NO. 13 " < ' '- ,. • "'·

'

·lo

·20-

·2 5.

·27

--

~~--~-~~-~·--"N"--------------------~

1 .. ,

LOA" ......~·~~

0 ~ ~ ... 011

-···'"'t ...

l.Ot. 01" 'rESl' BOi.IHC ~0. 14

0 +---lo.-r-i-·i-·-···"~i;iund Surf•c~ - Elev. 4a~~+---+----I (l.t1rk bcuwn org•nl.~ SlLT. moder•tl!'l.;1' 14-1

"

·l.O·

firm. mol•C:.

B~cO!llin& ~ S•ndy CLA.Y, fil"'il:, den•~, maiet

J'l.6

l08.2 15.l

l_(l'j. 8 18. 8

-··-., '"-... -- b·· ··,: .. •· ,;..;:,~°" DH<.-i~''"" ~,;;; •01""" ·'""''' ",·,·.•I· ,~;'~"" c•ucr1,,.,,,,, --~::--r-=.,,.,_,. J ,. ' "' """" ......... '" " - t '

'_"_'-+----+-'-_•_•_·t--·-LOG OF T~:ST HOillNG l'!O. 15 ---+----"-"_~--+~ ,._ .. _'--1---+-'"_""-"+---LOG=.:~ .. OF' T~:S'l.' ~IJ~ING NO. 16~~---+-·-_,.::·r ~·':'.:"'~ O·- ~-+----(;£r.:iutld Surf•ce - E:l.,.~· -1--- r--- Q· Croun.d ~ut:f 111ce - ~:1.f.'V. !!1.5 ____ ,___

1.5~1 i.irk br~ ol'g.11nlc SILT, 9oft to 73.4 23.2 I.I l-'1J lJ.Rrk hrOloln ~-1:.~0llni.c SILT, '!!()ft, mOil!l"C moder .. ~rly ftn111, 11tOist

~ight brown Smndy CI.J..Y, sof~. mbL5~

' ·1

109 .1 l].~'

'

I

I I I i

L' i - --·· _,, '" ·-"--"'"•-------·----" '' L_j Figure No. 16 -LOGS OF TEST BORINGS NO. 13, 14, 15,and 16

86

I

r ,•

j

l r I

l

l . l

f 1

[

[

r I-" ff ,.

' l I ;, «

' ' < '

·---·--------.. ·· u •••••• ,,.,"

·---"·"··•"" 1,, • ,..,.

'"'"'" . "'

File No. E 2204-·MI

30 November 1964

Loi 0 , .. ,, ,.,.,:, L,,,.,,1~ ~ .. •r!p:L>n ~,, tio"'"'"

J~;I H,_ ·~ Q""''''' '·•m,.,., l--+--1-·-·~_._··+--- LOC 01 ·n:!:iI BOii.IMC tlO. c'c':-----t--'·~·-1 • ; ;o Y'C

O·l---+,,-,_. ___ c_,_o_o_•_J_s_"-'-'-'-"-•-·_E_l_._v_ .. _4_30 ____ +-5u[t ora•nlc Sl~T. moist tu w~t

;

lli-cc..ain?; o~·.s.1111.li.: CLAY, so tr, mol.r.t

. \0

-15 B.,.c.0tni11g Iirm, .l!ltiff Cr.J\.Y

IJ Buting TRT1\'lin1:1ted at 17 (e~t.

--- -~---.. ··~---··__l· . ·L . ~ ...

··---·-1., , .•• ,. ·---~· ..... -'" '-·""'· l<' (•"""

, ' ' ~ ·• j, "

,- 1 -~--·-·~----·---···-\ ..... ·--- ........ ""'""""

--,~~!l~!-~~-.~9---"---.~·-d---:'..;.:;:\lnli ::lu"!.~.~-~!:;V . .:~-~---+-

D,,rk b-roWl"l urgant~ SILT, 801 C, m'1l.St

Lt~ht bro1.1n 5ilty (.!..AY, f~rm, dr-iu~-. iiiol:ll't

-··---

_,,,,.,,. ,,,.,,1. >'· ~· ·,., -·- --O·-

sl

20- l

10·

I" I

,!.3·-·--

·--.... ___ ·---·------- "'" --·' _....___ --·· - ··---

L,,A •

'"''·''"'· " DuoripCLun

~.,.,1 -______ 1.0G OF Tf.:S'£,,,!10Jl.INC N(), 40_

~+----Crom1d Surfoc~ ~ Elev. 602

-~------·· lo - r •••.• .. -···-:----

D=-t ~oC•<•>"• Q.,, ... , ,,,.,,_,

,, \' ! ' t ~'1 "".

--D.1rk brown SILT, ~~-;,;e-,~.~.:,·-Y---~---+--·------J

lie<.:t:i!Jl.in?. '"t'\ci.i:i.t

":~~:~~~~~:~:~--:~,-,-,-~-G"i'~-y~·t~ety motst

~f·.-:f~ Becomln!!. 5U.Ly SA.No, £inn, c!el'l.1>1:,

xir! moioC

t:i-'·

8"c0rt1i11~ vf'ry fi~·m Silty SAND, derise, .sllg.ttt.l.y mols.t

-· ---- ---t---+----1 Bor11·1g Icnrd.ri11ted .lilt 23 f.e-l!'t

---·--··-------------~---'~-·-

FigCJre No. Ir -LOGS OF TEST BORINGS NO. 17, 18, 19, and 20_

87

F1IH No. E 2204-MI

30 November 1964

'1-i-.=:- <"--- -~--·-·· ~----···--~-,.--------~------

i':~ " ;~o.• '~;'\""' \ '' l•ql• LOG OF TEST BOlll.NoG NO. ii r··-·1-- ·-·- .. ~ .. .,. GIOllfld ~UJ::"ff!c11t - ~[~,-.'-',=.~.~Q~JO----+---+---~ , 0' .. -- ·----L---.~

D.11rk bruwn SlLl, fin ft, mo let:

i 1 I

I"

UrO<h "•"t'I• '·"<" """'' ,.,,~ '"' ... '·'· " '""''' l.O<; (lF 'fr!1L BCrt!HG liO. " ~-···

O· C"E"\'.lund --~~:~~-·~-:-'- :)t..,:;

T Do:i>k brown. su .. r .. ZIO{J: I ~1011!1!:

22-1

' ) 1-' J..Lght h•own Clay-SILT, 1Lnz, i.'.lefJEI~,

rnnl.11.t:

·10·

. 15.

Light tir'1"'11 Silty SAND, 1:L:r:m.. d~t1!1e", LllOL9t

clay lt"(H1~S

U_ --------~'-~""·--------'----'---' L-~-L

1., - ~l'" ~----·-·-

L_) __ J_ ___ ~ •. ,, ... ~

j\ I - ·r.lt· .. _-----·-"-·u_·_'"_'_'_"_._~_·"_-·_--__ ----~=-'·"·"·'--"'"'o'---------<----+·--~-··'·" ,,,_ SILT. muC.t

Dc'lrio! hTriwn Cl.11y-·SU:r, soft, V~IY wet

10·

. 15

, ..

1. \,

2J• l I. \,

1. L I.

" '1 •

!_.. l_.. f."t"ay-bro~ .St.l.t;y CLAY, firm, m<.,ist:"

----·

"" "•. •r·•<l'-o< -~·- ~-

1---+--+----<--~~~,_..9-1'" 'l'KS'I'" P..OklNG HO. 2.4

0 ,,f --h-~+- c~e~nd 5u.r!l!l1.:e - El~v. 64(1 ; I H-rown SILT, !llofc:., ;:noi!lt

fl rm, dens~, i. 24-1 jfl' 1-\~t.:rnon Si1'y SAND,

Jyl

·10.

24-2 1: r ···r >1 I

dJ ·12 .. , ---'--'-'··:....~ .. ------·--------------

B~):rtng 'l"12r-·.11tn11t"d .rit l? fr;-r;-t

Figure No_ 18 -LOGS OF lE:S'J' BORINGS NO. 21, 22, 23, and 24_

?- • ,..,.

i---..,.. .. ~,--·~··-

"'' .:-.:1•;·

'··-

----i--

•• •

•• "I·

~-"· ,,, '"" " ~' .. .......

LOG OF TF.ST 1:101.il.f.IG NO. 25

0 .1---+~r+- CTm,1nd Surf.11<.:e - Elc_,_-~5~'·~'---

rJ~·rk brO'WTI S[LT, loo.,,e ."dry LL,ghl brofo/TI Cllily·Sil.;r, 11-0.t:i:. 1110'1.et

,, ·i: · .·. Ll.t;.1\t. brown Silt.y $.A.tH), fLI:m, dcn•e, :rt mo"'

2'- l ,,-1,· ·T.' ;rf ·W

l I [ t~J

:::c'~'~·~'~· .. ::J~(~l~1 :-l-_b_•_ccm.ing v1111r~''-'-'--'-_"'---~ring Tc,nnl.n.!ltei:I ll't. 18 feel

·-~------.M-••-------

·-~----~-,_,_ _____ _ ,,,,,'

:<'<ooi:<1

"

lo· r..,,

;,, ~"'"''• ~·". ~" \ "" ' •"' P·' I. ; '"~ ~' ·

------1 •. - ''"'"

"'' llhl «oor D<">L" ''<'"""" '••' ,,, .f ~ ,jf, M<.

+----11--f.::-''.'~"·'~'~-°"-'-(J'JI tE::iI BOilNt. .N(:c'·:_:2~1----f.. ·----l--+.cL-W.111ter Surftic~ ~ El.~v. ~'~'~'----! •• ... O·

I • 1, !, I

I lw I

• •· I,, 11

•

Bottom of Pon\i ----·---8l•1C.li: oq;l!lnit:: SILT, •oft

Bil'cOdl.lP8 .a "V-:ry soft P~:.AT (n .. ·11rly !>ul:'e org•nic~)

- ----····----------

18.7 275.0

File No. E 220~ ··Ml

30 November 1964

-· '.,~" >•~o I<

in Ho. r, .• ,

Loo I L>•>""''

,,.~,~·

~~·--'----·-+--~"~"'~OF TF.St' B.Okli;G MJ.;,_;2~0----4-

I

0- <:rout1.d S1..1r!•1.:e - E}~v. 540

511~y S.AlilD with grmvrl. luu•e, mo{~t

LOG OF TF:~T JIO~ING NO. 2.8 "• """'l<' ,,,.!.

W~l;e~ Sijrfmc~ ~ Elev. 620 O··~--l--t-'··--""-'-'--"--'~~~,;;.:;:c:__:_---'-~~~~f------f-

5.

·J.Q.

· l.'i

BQ1;t0m. of Pond

sotr PEAT

'.:_'.fl-.},~( . .Bl•ck O'l'."p;.1mtc Stlcy SAND, mQde~~t"-~·l.)' 1U·l----t'"-'Y--~f~'~"~" ~· ~·~" ·-----~-

Bor 1;;g Tcrmi.n•t.cd .at: '20 fe-e·t

~oio:.u

'~'""' ~ "~~ ~-

Figure No. 19 -LOGS Of-- TEST BORINGS NO, 25,26,27, and 28

I 89

File No. E 2204-MI

30 November 1964

"" II••<~ ,._1. -~~,.., 11,..crl1><l"" ~,, .. ~r ~·n>\Vi Cor.'""'

f'-"'-'+-~~'---"-1----·~=::::::..°'::o."To•~soT:.._:J!IOlU.ttCc,,,;;•ooc-_o'='-----1--~.<. r. l ,,, .• ~' ~-~-~ Surf•c~ - El~v. ~25

o'--"--1...-~"----------

,.

10-

-20-

. )0·

llol;ti;n. of Pond

Bl•~~ ors•nic SlLt, •oft, w•~

····-~~-----'---"---'--'~-J

hrQ'llJ\ Silty 3~D, fLrm, ~o{~t i------W•1~--ll------

. )2· Bl)r1nL!!,~l~t.""_o;;=,;:_··='-J='=-c'c•c•ct::.. __ _,_ ___ ,

·------------··~'"'•'•

1--__..:::_ - ''·.~.'.~---.. . >•...,l• Lo.:>tL:><1 11,·,

~'"''·'' Coutr· ~-1· ~-<' !. l ~.·. ""·

-1-----1-----"LOC~"_!O~F IE51 BOlI,•oc,,-_,.,_,o,,._;_'1,_ __ -<1-~~~..___

· l.O·

"" L•wo;1-

" ... ~1·

LLght br~ St,lty SAND, fi.i'.':lll, d•tue, D!.o1st

bec.Qllllng: v•~J' f1rm

---~----·· ~-·---------------

"''' . :i..~'" r . .,,,n\~ ~~. ~I

<'-"_'-l-----'C--'_'"_,_ __ LOG CfF T~ST BO~IMG NO. 32

0- ---l----l---------""~•oo~u'!'nd Sur~aca - Elev. ~jO l.i.ght br;:rvn ... S°.M1 SU .. T, loQ•tt, dry -.-. ~·.~~"-~~-~ , 0 .1----1-~-.-+----°'=coe:u_:i:~ .. -~!"~.; Eltv_ 524

Datk bl'OMR SILT• lQo"I!':, dry

5-

lO ·

·15·

l)-

Lf.)!ht. brawl'I. Silty SAND, firm, clat1.11ie, mol•t.

--~-------------

·--~---- ---------·---.. - L'

. ~ Whlt:~ fo••il.i~~rou• LIM!.ST~ con~li;im~r•t•, d~n•e, firm

_.L, _ _._ ________________ _

Figure No. 20-LOGS OF TEST BORINGS NO. 29,30,31,ond 32.

l

l

l

I ..

I

k

-· i

I ' ' ~-

1. l

1.

I I I

,_

10-

· lS-

I. -I 20

I

"" , .... , .. " " .... ~ ~.

""'· ~ 1~cotl>• ..

_______________________ .. ___ ,. ~pU'f\I''''"

__ _L__,, -

------------··---- ----- ------~ ... • c•'<lon u,.,~::;\Y ~;;;;~~·

File No. E 2204--MI

30 November 1964 -~ ·---<•-- --··· -----------~----------

·'""' "

L"'" >J•Oll '"''""' •o ~{

~.~,·~·

Q-··

5-

·J.0·

:- · . . ;. ~: :: ..

•15·

_ ___;U>G= Oi' ~.!_~C No_ .14

Ground S1.1?'f'•c~ • Elev. ?2J

L--!'.: ~-

'" ,·,,.-«•< ._,,,,.o

,-·--------·--- ·-··----------·--1-------.-4-----< O.ril; h:ro..m arg•ni(; s.~1!, loo~e, dry

---------inirk bro"'"1. :)i.lly SA.Nb, flrm, d~use, moi•t"

----~-.::l_O:c•_;·.c) ~

------------·----~~ .......... _...,___,,,___.,___ i.... 1., .. !"i•<f

... IO<Lp<I•••

·-· .. - '· ~ '· ~~- "'" _ ___, __ ..__ _ __,_ __ ~J~;~t OORIN{:. ,.io. -~"1_5 ________ 1 ___ ,, __ ---{ ~

,_, D•->\" ,,,,f.

""' "'''f< ('""'"'" ·.~ ,. , ..

Q .\__.J_, _ _j__~ CrP~fld~~~-~.!.~::'. .. !.-_5.,'.J_7 ___ •--\_--.!---___; L11Jh~ hrO'Wfl SILT, loo•e, d~y

I , I ! '

' I I I ' !-

lo

. )1~1

-.... '

'-'..

---+-

.- L__ - - ----1----~

L _ _J_ __ _J_ ·------------·---- ,__ -- L .. -

O· ·-~::-

· ..... 36-J.

~ .'. : . .

.16-2 t~ ..

·.lll ~ _- -

~ __ - -

. ,:_i:

D~zk t.rolo'n, sli.p;lil;l,y Cl011y.t1'y, 5andy Sil.T, fiun, moH1r.

,I· ~. Lie;h( brawn S.i:lnrly SILT, fLrm, \~':!;11~c, nieoil:•E

----------··· .. ----

100.> 111-7

jzo 1-:,::c: ' ]:·.';'.:.·:· Blue-gr.ay ~AftD, 'JCT:f <:l~n:si>, mDi.11.t.

I: 22l-----''-"''•4------ ... ~--------------+-·-t----l fl{'!~ i..t.g TP't"ll'llI\11t.ei3 111~ 22: fl"'1"t.

I

11 I ; I I

____ i__L -· ··------· .. ~--- ···-·--····-·---- ---~-J--,,, __ ,___·~

Figure No. 21-LOGS OF TEST BORINGS NO. 33, 34, 35, and 36.

91

File No. E 2204-MI

30 November 1964 - __ , __________ _

, ____________ , -~----.... , .

l<ro<!>n .. "--•I•

LO(; OF "fT~ST ~C?MitlG NO. )7

O --1-----1--~-.--I-' (,:roun,d S111'" t.ui:::e ..:,,.!,!-"'". '.li8:.._. __ _

. :n.·l

'

-10

,,_

.l{)

,·:· ·;:-·

~11.\ .. J_.

Tilat:k orp;t11oii:: SILT, firm, iDoi..o;t;:

In - I 1., •

l05_ 7

~~, "-"' '""'"'"'

l9. 'J

J tli1 ' : 7 tj_ ~--L- ,_._~_;_-'="=·-,~-:-_=_-_,_-"=·~,-~-,-~_·_·~~-'~'~-~'·-~--~--~~-----1----+

.

.

38-1

,_

10-

----------~------...-·-' '• ], '·"-'•

•:.~_~:_:._"1----~LOG~ OF tES;·;:·~~-"°~· -'··'-----+ -·-~-·-1--r_,· ~-~-'.::___,! --i-------'1;_~0ound S .. u~fac• ~ Ela-v. l~ ---1----1--l.-•. -

1.I

D~rk b~01.in SILt, loo•~~ mol•t

J.07 .2

~>*1--'-•_c:omlns firTQ

.:;

-:. G:rt1! S•1;1d.y SILT, flcm, drnae, dry t.o s l.ghtl)' moi•t

;_. jF I!.T~1 5ilt:y EA.ND, !t.:tm., dr:Y

1r1 38-)

·18. JJ,;f vory '_'"" ___ _

----1------+-,·-~ Jl.orlng T~rmlnat<1'd ilr 18 t'eec

-L--l------------------------'--~----

5-::."(f:f Ilerrk l.JroWl'l :)11ndy SJl.t, f:l.nr., moittt: to

'•O 111 o<t

~-~ Iil~,.-_,. __ -'---------~---- ' ------·]fJ· ElorL11g T;-m!.r:,~t~d il't 10 ftec:

~--'----'-----' -----------'-- ~J -·-L- ·-·

Figure No. 22--LOGS OF TEST BORINGS NO. 37, 38, 39, and 40_

92 [

~.,,. ...,, ' ........ ,~ ... "' f----+'-'-'_'-t----·-=-•_O~r:--:r~<_S-;:T· ]!OiC.IMO 1'10 . .l,,l.

[. O f----+rrrt----~~~wi.d S\H:{•<r<'! - El.,...,. 41_1.0

D.ark ~.J".,..l'I 5H.T, fl.~, •tJf.•t

I I

lO·

' I

---·-----·- ·-·---::·rt Li•h' "~" ""' SANO, ""'· •o"'

f'f

I~! -A-.-::-:i.-:r:.t: b"~~icig vecy fin~, clenf'IL

JJ - ,_J: •..• ------···· ----·"··---· ~ori.11~ "Ienul.n.11t:lf!{I 11l 17 feec

I--·· ro . r~ ...

hou:.••

"""' '"' .. ,.,, ....

L_ _ ___L __ ~'--··. ----------·~- ----.. ~·---·· --··

rr-·· I "'' ~ !'" I .•• ,,,

> ·----+--·-- .

l7

I I

l '

i I l_._J__.

________ , _____ .. ----·- --------~•I ''I" IM

, •. •11<. __ . _ _....__

~,"'-'° '""'~'' . . ,, ~,

___ ,._ _____________ ··-+---t---t Borh1~ terml11A1t:~d -"'!; l."I fe.et

·-------·-----------'--'··-- __ ,.........,

File No. E 2204-MI

30 November 1964

-1...>,11.

rl•••~ '"~P!< , ........ .... \o fl.:>. " ~-L· , .. ,

.').

. 10

..

Gr .. y S.1mdy Sli.T, f.11!.1"ly fti:'lll,, d.'€)1

Light. gr•y S111ndy SILT, fi~, d.t-n!ie, l,'l\<)l8.!:

--····-- ····---------

"''''''' ~r. r •• c

··-- ·r---"'-·--- ------· 1.o; ft

''·''•Pl' '"''·•\I"!! ''· o~ ,....,,,, .

~•••• 1u.ion

~-f--- f--f- , ___ LOG OF if.St SCRlNG l'O. i,!4

Ground S111'111c:c ~ Elev. ?.60 LJ·C·-- .' . --• ·---····----• --"="--"'-'---

'

1..0·

. 4lT-l

., '· .. Lithr groy S~11Jy SILT, J.oo~c, d:ry

.. ·. •',"

-o.•'4~---------·----·~-

?·j'.J: ~-~·-''-"-b-'°-~ .. -"_"_' l_•_y_-_"'_"_D_, _f_,i nil. I 1110(.gt

...... Tl~rk browr1 f;,111ndy SJ:L'r, fi.l"ffi 1 moist

....

:-. ',

::.:· ,. ·. ·:r-i+H-1~- ·-------·---.. ·· 1.lght hrown Si.J.ty SUID, very firm,

4'i-2 ~::- ·:r: cl~n•e-, moi.•t

·'ZO·

-Ll .~~ •.. , ---..-~····,---- -------

!,\(.'Iring, 'fl!'~in.mttod at 27 fe~I;;

l09 .(>

"o ~ ""' • :.,,,, . .,,

ll... "I

~<Y "''"·''" J1,·.•,r, : .•. ,: ••• ' \ ~ ~ .,, ~,

L---"'-. .. _____ ,, ____________ _..._ __

Figure No. 23-LOGS OF TEST BORINGS NO. 41,42,43, a~d 44.

j

i l l ) ,,

l

File No. E 2204-M!

30 November 1964

L~1 ~

":ol• ~:'\""

--~-"-'1-------!LOG~~·~· iORlHC tiO. 4:!t

(j L ... , __ -_--[ ____ -__ ___ G.:.t'"9".!I~~.~~&' _ F.leY. :~90 Dark brO'IJn Sandy ~ILT, loo~~. dry

. . ' . . _.. •"

: :. ·,, . .. -

'

- lO

· 2G

·:·;; -~·: l..1.iht bra'll'tl Silty ~ND. 10011~, fl!01.•'C

}fl ll --l-l[l 11( :l{t r1t Jl

:}~!;1 I

ift} ,, :ri-.J~.____. ___________ _ _ _J/c__Jl __ _J_,.~,~-·-o_•_ln~:~:.1~-~·-"_•_d _'_'_'_'_'_°''

-·-1---.. m~

-- -·· ·---- _,_,, _______ -----·~------ ··---~ . .:..-: · '.'..·.:::__

a >---I--

W-W_j_- • ., ----~•.,·-··-----

t•····

Lo~ ~ , •• ~11 .... , ., ~,,..

'' ~I :;..,r••

l.o• ~ "~::~ :.

So~plo

LOO Of T'XST M.*l)IC MO_ 46

°'""''''''···

. ().~- ... --_.--+----'-°'oc''cu=o:c•d:_.,:'.iv\'"f~.:;:~ - :El.ev. 371

Dark \.>rQ'"JT\ 5i11ndy SILT, loo&'<", d-ry

5-

·10·

"

10-

··r:r Light bru\'\'(J ::;il.ty S.UfD, fl~, icUL~c

rl(

)_:1_._11_-· 1-·-11[

l1X f'l J}ii Ih

-•·1J1: ·:H._: .

1~ .• ,..,.

:""'""' ., ,.., ~'

. 24.L....---~L..>----.. -------....................... ~ __ L Figure No. 24-LOGS OF TEST BORINGS NO. 45,46,47, and 48_

(.

..

l

I ;j • ,_

I· I I I

"'" :o:<: ~ ,,

--------··---~

I · · ' I "t -· -·~

~'"' "' n'I""" ,, .. , .. , ·, ~ ..

LOG Of" TLST l:\ORI!!9,_._N_0_._,~9----1-- .. ,., __ _,_ __ _, Gruund Surf11cc - EliF-v, 111~ ---------+--

gr•y s111n-Oy SILT, 5oft, ~0L1t to

'"' _ W/L 7/27/60

f-'vi---f-~4-,l\oo;;;,c,,;--,l;;cr"UkTll1:0'i'--·~,~-----··=~----+-----__,· ~ becenLn.g fL.tm at 111 ff'""t;

'"I '.:Jr )IL"< ••cOmlng • very fJ.-.. ShND I ,; .~-~--~··_--._-.-...• -,_-,--o_r_(_n_•_T_e}·1~,L~~!'ted at .)fi f"'-,·,-----f----+--·~

~-.- ..... --.~-~---------

.: .. ""• ~ ,..,,:, "O<IC !>O .,

- lo · •!•«

~"''''"' c,,.,,.o: '-ol• ., c ~ l "' , _, .

. -·~·!:,UG OF TEST IimtINC NO--:. .. -.~~t----+---f--O·C---t:nTf-:C-- Gl'.Olll'id t:ur!~i.:e - F.lcv. 660 ___ --f---+--

20

Bro;;n to d.1rk hrc....,.,,, o):g.:i1ii<~ S;:indy [: SILT, fiI1:1, moist

V• ' ,, I ,, ~: ,~

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1; ,, '"

,.

v ,, Yy)'

'>'y )' )'

YY, y ,. )

l>"y y

Li~ht hr0~n Cl~y-SILT, wilh mln0r frngJDl'"nt~, stiff, firm, moi!;t".

rock

bcc:omin~ '1\0l"E' ro<:ky

-----------Ct"•d1.ni'.!, [0 "'~:t:y Cl.11yt-y w1>11thi:!t~d

Fl•:,~1t!.1: Jl.ock (r.r,,"ri•tnne), dc1ll!IC, frai::~ui:cd, mol.11t

>~ Y:> Y/)

. 2 l·t---f-'--~"·~-----------Borln~ Tctminatcd ~t 17 lect

------

File No. E 2204-MI

30 November 1964

....--- ~·- ~--~-------- -------·--~----··~ --~-

,.~~~.~'~ " '·~·.~!·

>--+--- .. ···-·- -- l.oG OF TE:ST BORt~.S 1-!0. 50

I• 'I•« ~-~--·~-~~

Mn',n T< C<,·11• .. : \ "' .

G~c.iunrJ t:uIL11..:c - Elr:v._6_6c5~---->

li;i-o'l.ITI to d1n·1<. lirowB ~.ii"1<:ly .SILT, orp,11nic, ftn~, vlet:

>··f--~H;e'\--------

·10·

L• Lir,ht br'1wn Clny-STLT wlth t11i1)0l: Hic..:k L• fr;:i1µ11:.nt~, l;ti.ff, ff1·1i:1, 1cioi~c ~ ~

~ ,, ' ~

. 1 s ·f--jl"-''!-'if-------·--, y _ Y/y

'Yy yy;

Yy

Lighc browu ves:y Cl.1yr.y WC'ilth1?re-(! Bll~alri.: Rock (Gr~cn~lon1~), do:n.se, irll(.;Lured, moi~L

Y::' l>l:'Cumlui; vety (i..t.m ·22·t--+-~4---- ----

Boring Tcnnin~t:~rl .e:r 22 ('.!et:.

-·r· - . -"·" --

n,,.,, >a,.lr lo~ ~

Looacl.1,. ~"""fLM!'"

" "'·

ln • ''•" ""'·-· .. -·- ·.------

~ .. , ~o!i:"•

"·•-\•>

tEsr 1'.'?MitE!£_~~------t--'-'·1

:_:__:

~·-r !• we or '"'

D· -·

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lO:i

/

j v · 15· v

YY y >', YY,.

. 20· >"Yy ,,. y

vYy

y y~ yy,.

-25· 'yy yY

·21 f-- x..v

Ground ~-~~

D11rk brown, or mot!e.r11C:.ely f

Li.ght; bt:01""n Cl )""0<'.:k tr11:gm~n

. 8&>c1:1r.dn~ Cl.t)l'e

Ro<'k Gte~nt fractured, d

SurfACE'"a~. El~v- 660

g-11ni.~ =:;ani.Jy SILT, '""'t, {~

11y-SILT with lo't!11Cl~ered C:!I, .11t:.i.ff, moi!lt:, den-1!1~

y, We11ther~d Sss11l~lc cone), 11ltE-rer.l, 11I'lile, rnot..1t

P.Cl:t'ing Terrain

.

Figure No 25-LOGS OF TEST BORINGS NO. 49,50,51, and 52.

95

File No. E 22Q4~MI

30 November 1964

'i\

. .'(i

. L'.>

5 'i- 3

,., ~-Y Y ,. y -~ ' .>''

'/~.f ___ ::!..L'

Mti'cll11m bro\.171 Silcy CLAY \.If.th rock fn:1117pn=-nt!ll, wcach~I'.~(! f"C~ pi;trcni:. l"(>i;:k, di'n~r., moLiic

B~(:Ond.nJ!: 7'.r~y-brawn <.:UY wl.th w~.ittb~rit'cl P..11!•:u1lllc.: Roi:::k f:l::l!l~(ll:'i\l;S, 1o1~t, soft t(") mr.dium d~t\!1-tl

ll..=-n.~u gri'crii.!ih-g:ll!.'f 'Wf;'tl'thPTi>d B.1.o;;;alt:.i.1.: Rock (Gr~~u:itol1e>), frflcturr.cl wii:.h r. l fl}' ~!~ncn~, mui.l!lt to WE>t

118.0 l6.9

112.8 25.0

129 .a lf.. .1

_,, ·----------+-----l-·

l:lll•~~?,rny, fr1:KT:u)'"'i'il, cl;iycy ~Ji:tp~l'l.t"l.1l~ rock, wi~t., f in11

--

~:;,. . '

81.8

\IJ,8

92.0

-----

Pl•••

~'~'""'

1,1,. 5

)f,.4

)R.g

L:I.

... ,, l

"""'~ ·-~·· l~·-1-~o ~I

~·-"_' +---+-·~'-"+-----=--o~r n:s't l<*t.»G "°· ~ ~-r.t---~Cc•cocu=nd Su.rf•C~ - f:li:-v, 595

Dark J.'"i?"d<l:l•h-brcrwn Suuly CUY \Jit;h

' 1 "j·

-lU·

·I' 5.

)"y

YY /j /y y/ 7'.,, y

//: y y yy YY YY //, Y/

Y/ >

5<:Xll~ \,l~~th~r.~d rock fcagm~nts, mi;i~~t,

•CLff, ~e~tlllll d•n•~

l"i?"CQmi,ng we•t:h~red, fr.tctui:ed, Vf!ry soft, cl.11yey :rock

~ ~/L 6/28/63

w~.ai:hie-~PO rnt'.k wiLh fct-quent <:'"\.'£1'f i!r-~1!"11\S, w.-:t, ploi~tic

"• ::-~'r " "' "'

109.:2 17.2

20.l

'21'1· ~~" - .. -·------------+----+---<

"""" "

u·

,.

10·

·20·

-------------,.~""-·--·- - •••<•

~::~~ \1 •. ~~!, ~,,. -· ~"' L•

... :"·1·~:: .. -_., --··.,y =··''""'

1.(l(; OF TEST BORING ~0- ~6 : ~ - ,, .• ~. ---i'---------..... ____ --~---+- -----c--------------

h·~·+ ____ c_r~,ull~ -~~~-St;. - i::li:-v. 5'•5

C----t7"*+-'-•_c_·•-"_t l y ..-l~ .. ~:~.!._~~~-.E.!._L_T __ Den~~. yellow~hroYn Silty SAND

.0. ... ~;::

·'P' ;l1J' "'~tiJ

CCMP,\CTED FILL

Dark \;,:rO~!I Silcy SAND wiLh sot'le c:l21yey reek 1~·1:1gtu~r'lt:tS, mot~;t:.,. den~~

">---~+---"·~"-~-----···-- ....... ·-·-----

----~-... ___ ,.,,,.__ ------------


96

n u

r· '

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11 ..... :. ~•'.~• ~.m

~ .... ,:.

,_

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10.

I

20·

·J ·lJ

I , -.. ,

;I

I ,.

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J

Ir. - rl•«

o.~:::, ~~;:;:~~ L0C OF TEST~~~ NO_C'--''~'-----1---+-C•aund Surf1:1ce - ~;l~.'.-~---!----lf

¥~ll'-""-bro~~ Siley fine SANU. Ucn11e, lilightl)"' \~~Oi.!lt

CCMPACTE'.D Y .(Lt.

File No. E 2204-MI

30 November 1964 I"'----· --- -~-·-----•-r""~---·-------------"

'·"• ~ '"'"""" "

P<l<Ti"10a

I".'''•• ----~----<

"'' ~ ...• ,, ,. ~<r I~°' C'' «•:

l.OG OF TEST Rl)R~I~N~Gc_~N<::.:·1.,_5~8-__ _jc__':'..~~1-~.~~. of. ---f-.o,.,,.+---·0"ouucl Surfo;tcir. " El~v. 660

D•rk hTOl.l'l'l. organic S11ndy SILT, wet: -~ 1---' ~- L---....,

,_

·10·

..

·15

.20.

·:l5·

. ]()·

· 3S·

40·

Phl'44-~~----~~-·-

, __ ,,

,. ,, l

l--

" l , l

" l

I, t gh t brown Cl.ay~SILT wlth Weath•l"i:!d ruck fr~~~nt6, •tiff, ~oi~t, den&~

-i,,y Y R;:>comtng w~~, pl"11t1i:: CU\Y :ln .i111i::~red

/ )" ri;ick

~Yy

"'Yy y,,

W/L ~O miaut~~ afte~ ~pnipl~t:icn of t10i2

Yyl -• y yf____y_~ r.H/L 2/4/64 c y' "'Y; >'y > >'yy 'Yy yy 1>;/ ~>~;;;:,. y4-------~-~~.---_,,r, r_,. Bl!!'t:Oro.tng t"l~ W'~aChRr•d Toi::~, bluir~ ,;:. ..r, gt'a.Y Sm-~~ntl.ne'f /,,.

;_,-:;~

~/'. //; "..~/ v/ . 48·!----i:..::-'l--------------,--cc---~,~-I-....-~

Bot-lng Tlf'mln.aic:ed at. 48 !ee~ ··---

I

Figure No. 27-LOGS OF TEST BORINGS NO. 57 and 58.

97

File No. E 2204-MI

30 November 1964

·~----~~ .. --

10

,,

. 3~

.,,

·l.O·

B•tiwti ...,111'itt.here<.I 1'>!1'.'ll.11ltit: ll0ck, very cLlllyl!-1, 1;he1:11'~d, moi~t

'-'.-~,,'-'-C-r-•-y·-1-,,-,-~-.-l-{;;e-d-Cr-•-•_n_•_Lui\~ }l.o~k, / y' very cl"'Yli?"Y, l!ltlff, denll'~

.>'y Y/ ,-/ y /Y '/ /

>'}' ·yy

y

YY Yy

YYJ >' y) >'Y' /Y YY /;>' ,\'y

/ Y/ ~<---,--A-------·--- .. ---

/

Bect1mll"\(( hlu~-gr~y S~rp~t'ltlne rt)c.:k 1 Vlli'"liY c l11y~y, w~L

/::. ----1__ W/L 2/4/64

. •i•'• ---

. 4J·

!;::::j~::J:;/:::;/:::;-bf.\Iil<i'il:~'=:--

·?O

-~ I

r -~-- -----~ .. -----·------·----L ___ ,

'·"''

~:·IC•''O C-<·• •0 LOG 01 Tt!T !.Cil.I~ t-10. 60

Groorid Surf11(:ot T~El11v. ~52 0.1--+..=+-----== _______ J,.~~-·- .___ _ ____._

'

. 10·

. 15·

zo . _, v

·-•· , ..

,[,

v I•

"

y'y •

/,--, Yy; "Yy

Light. b:r(Wlfl. s.ndy ,';U.? vt.th cl.ty arid. ve•ther~d rock !r•g'llll!'flt.ll, t:Lrm, Mi•t.

Gi::~y t.o btown .;.,--;;t.hered Bt1,o111lt.Lc Re>~k {C~•~n•tone), •htmred, •lt•r•d wLch ~•ny cl•y aA_.•, very fl-nii., d~y to ll'IOLll t.

'

. ]8-1--~~'~ "' -"+--·----·

___ ._"_'_l_""_T_._""_1_ .. _._,_·_·_·_'_3._'_'_'_" ___ _j_ ___ ,,L __

Figure No 28- LOGS OF TEST BORINGS NO. 59 and 60.

1r

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llrD'lm to lf,ght. brawn Cl9l'ol!'1 :!':iU • .'r wlC'.h S011nd

Light bt"\•w11 cl~ycy rodi: ( .... ·e~tl)~.red Grccnst.(mC'), ft.rm, st·i(f, moi.~;l

Gr11y-brown \.1'6'l'ltheted B;i5"ltic: R,1.-.~ (Grc!"l'l~ton,:.), fi~·m, b.Jn! t·•10:.:k ;.,·ith "'t:!.Jll11:>r.:-d .:.l11y so:-t11~i:i

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le.· Cl"'

--

--

·-

File No. E 2204- Ml

30 November 1964

-··-· o.

'"•A "='<«Lon

" ·'·~ .. •· f--+-----=~_01 'rEST ~~'~'HC NO. 6:Z

··.'=' .. , ..

·"·-

Ground Surf.111c:c - .. f.lev. '660

f\"(O~ll Sa1101 !;iJ1,.'i \a>'lt:h i:-ock lra~ent5, moi~t, looR~ to m~diurn d~n~~

:~ ~~ ·~: >-r---t:''i-l'Jd-,~C-i-.-,-"-b-,-~·-,·-C-!o_y_•_y_S_ILI 1-1{1;.li V!!ather~d

"~1 rock fugmon,., "iff, mo!ot

10· ,j; ~ ;; .. o,

bec0111ing more rocky

i? ; ' · 1::; f--+y~,,~,t---------~~~----

Gr.Jy-brown WP~th~r~d ~lt~r~d B~~~ltj~

'20·

>Yy Rock, fr,ceu.-d, o\•y<y, H=. moio<•, y y> dcn~c

>/y ly,.-

lly y~ ,.,,.., tyyy Y/, becoming v~ry h.;ircl ror::k

"' ~-.. , .. , ~c:•c ~' c:,·.1.r·' · .... , -

.,,. ,.. / , 2&-f--f''~Y+------~~-·····'-··----·--------+----1-·~-~

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----------~---~· -~

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Ao:rlng, termin.11tr1cl .11t 23 feeC:

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Figure No. 29-LOGS OF TEST BORINGS NO. 61,62,63,ond 64.

99

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File No. E 2204-MI

30 November 1964

J I

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r--.-"-----·--------·--------r·-----M .. r I• . ~'"' ---

"·"·•·"" (o"''"' LO<; OF TEST '.nORING NU, 65

---C-u~-ce - f:l~v- 402 ·-=+-------··----.. ~·-'---'---'--.;;.-'--------+--+-------l Li15t"i~ bro'lol'"l'i Sl.lc:.y fi1v~ SAND, fi.nn.

dt.-rtR'-', mot9t

i!.Lui!!~hrown Sllt.y SAND, v~ry flrm, 0~1111•, mo1:11t

--~--------··- .... ------ ..• ...........---- ·---·~

---·-------------,------,-

l._ -~-------

'• D•'" l<V o.<.I.

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LO!;; OF T!.51 ~I:MG HO, 66

Ltgtic br°"" SLlcy ftn1> SJJID 1 filllll, dami•, M1at

:&luL11h~gx•Y Silt.y s.AXD, veory !1ni, danli~, ~oi,ai=:

'"'' ,, ~•~o!• ,_ Lo<•< l•" CH,1c~i>< '"" ., '--~· ·- ~-~~ Of T~'.ST BORl~ NO_

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····----·~ .• !.._ Bortl'l.g 'l\.•"nL{ri.ilt<!r:j 11t;: 18 f'~~t;: j

Figure No. 30-LOGS OF TEST BORINGS NO. 65,66, 67, and 68_

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Cu~ Surface - Elev, 433

Brown fjn,,. SANP, fi'.L'."111, moU1C

Blur-grny SAND with ~h~ll f~~~e~[~ (Lime1tcnc-), firm, cle-n!l4'!' ·

----! ' . r ~ ,,. "

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5·

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File No. E 2204-MI

30 November 1964 ··-----------------

l..OG O'L' TEST !IOIUHG MO. 7fl

Cut Sllrf,t11c11 ~ Elo1t\I", li~S

!lrowt!. £Ln• SAiiD, flrm, d•ns•, fl)011t. 51:11111e lL~e•ton• ahell fr•!ll"'•nts

Blu~~grsy S~ndy SILT. flrtn, moist

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Cut Surf•c11 - F.1€-V. 4l9 D11rk F,T!!IY .S1lty CLAY, \lt!ry stlf-!-.-,,-=-.-1---l

moii1t:. 98.9 12 _.lj

Stiff Silty Cl.A'!'• dena~

SAND l~n11

Stlff Silcy C~Y, den••

'18- -~ ,.:;;.;,::.;:r,,··---~~-~-~-~-~~-· 1Sorl1;1.x 1.@'J'lllll~tie-d .et. 18 feec


IOI

File No. E 2204-MI

30 November 1964

···-------·--- .,~-·------··"-·-_ .. _ '··-~:-~

'··'·"•• l·m

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0 l--+~-4--- .. -" _!~-"-'_S_o_r!_~c~--_,_,l_<_o . __ ,_1_0:. .. ~ .• ,,------+-B.n:i'lo'l'I ~Al'l(J, flrm, d'!''ll!I", mcl•'C

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__ ·--~.!~ST BOM Ul<::_.~.9.:_c725 ___ _

O--·--_J'-.-~4--~----~.;1l'ft11~i!r - El~v~ _!1~6~8c_ ___ _J llttr~ gr11y SH.t 1.1j._tb mlnur cl•y, v~ry

l!ltiff, Cl~r'l•~

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Cut SurflllC:t' ~ [l~v. 46~'--------1-

~.r .... .-:1 LL~t b•OWl'L 51.l:ry s..urn, fLtm, drri••,

i+r mol·"--···• ---

Dnr~ ~rCJ'WTl SlLt, •tlff, d~n•~. ~iightly !IU):\.•t.

--- .. -----· ·----+Jt D•~~,:~- '11'1 Hne 5'•o, f!em,

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Borlng t~:ntilnat~d •~ l) feet.

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File No. E 2204-MI

30 November 1964

Lo;, & !'Hpi• 1"'.••CL•m

"" ol "··~l·

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L((i or TE5t BO..IMG "o. ,8 ·•·-·•·-'----~~ ~-----·w~•-

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. ...,._,. ...... NL..., __ '""~~:-~.f!;,•~.:,~!..~~ .. ~].9 ___ __,f---+----1 •::::_·:: Ditrk. retldtah•brown ftl\e- S.4.~P, fl.rm,

det\•e 1 1110L.111t

vary t"lr.:n,

---·------------------------·--~

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~~-:-i-..... ~··-· ~~~'.:_ 1----~~E.!...!!:!!.,.~Dlrn~G NO ... !'..~- ----+---1-'----Cu ~ Sutf11Ce - Elev. 488

D· ;--,.~·.:: Reddi11b-br;:iwn SAND. fl.rm. dec'll!le, moi?it : .-.: · .. , ~·.:.·::.

·.-:-: . .-.·.

-------------------'-----'----- l_L__L__L_ _______________ JL_ _ _j_ ____ _


103

File No E 2204-MI

30 November 1964

·r·T·~ .. 1-,·1

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. :~~: ~, .. _..,,;, i,.._ ___ LO'~ r)1 TE:ST J\(,JlO,NG NO,. 8\

_ C11~~ Sur fl!c~,.;~~~o ____ ,_ ~---I.---.-~ Reddii.l-'"hrnwn SA.tit.I, fltm, dt?n~c. motD.t

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(!~fl:.h:', moi~t

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---- ·---------- ______ , ... , .... _ I"· 'I•••

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~:~ -~" '"> "~"'~" , •.. :.

-+-------1·---'::~.!E.!. BORil'IG NO. ~:.le_ __ __,

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--'--~J------(:•\·~·t" 5utf.:J•j'~~- ~:\.(•V. 609 ... ~--- ~- ... --~ D.ir).: l>~·(,wn .,.ilh I~(ldi.s.h-hTown 1~1,St?S,

"'·'~~ti "J· .. ··-.·['-:: ··1: •.: ·'1'>1" .=::.'·::::·

S;1ni:ly SILT. ra~Ui\.n\\ ii.--.-.~", 1o1i=r

l,tJ>,h'.: hlui~h-l',\"-!IY Silty fl.110:- SAND wi.1.il (l.fl:1, "IC(, 11•.;.~i!lm Ct'll!li=

['.:·,1.,,.n fi;i'"' :.~Mly SILT, ''1•'~.sr, firl"', (!i;>n!;"

_____ ., _____ , .. ____ ,,.~·-·----.1..----l----' f\_~I"~nt!'. "1°1:"11\ClJl.JlCJ ~{ l/j f,'i'l

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P.l11t'-F.,r1:1y S.i.lry fi.n,;- SAND, .. ~ry fir.;i, n1<Ji j;t

slightly i.:l~>'~Y .... ~t.h mlL\(I( j',TtlVPl. v"''f dcn!Se

-----

i----!-2C 0!1' TE.S'I ~.?RING NO. 84

D.irk b):own S.;indy ::>H.'l' '"'i.tb ::erJC!:&h· br...,..,.·r. "1I1y~y l'-•l'\ses, :;ioi~~. i•1e<:l1.~•!':': de!ISE'

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Figure No. 34-LOGS OF TEST BORINGS NO. 81,82,83, and 84.

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·----1------'""'..'.. .. l.+'"rl Pnnd Bottl:l!D. - El~v. &16

lliirk brown L.>t'~zintc Pi".AT .,..ith le11Sl:!9 of r.-.ddi~h-brl.!wt1 pl.nzit:lc clay, vet'y 9("1ft, wcl

flf"comini!. blu~-gI.::iy Si.icy SAND, fl.t:m, d.-:n!i"', raoi.~L

Cr.1ding l(I brLI'lo."1! 5i.lty ::iAL'lD

"•• ~O".IO'Jrl CU."•iov '~""'m•<

(. ; ~'~ ~,

__ , __ ---·---··~ !- ,..,.

L.___. ----

1· ··--------·----··---. -·. . ··~---···---·---·---~

, -I-;;-~. "' ~-··' ''""""' e-·---·---'1_·-_· '_i_ __ '°'LOC"--"'-OF_,TEST BQ>I)lC NO. '7

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~--r-"1-----'-l ~ Jli;. 1 0"".-P..~1:1.~L.!:.~t". 'co·"o"c' ._c'c:"c'_v,c._,0"1"''--------+---+-------I l"~rap0~-!!iy l'r.:>;:rdw-!!y fU,L

D~rk brnwn tn bl.11..:k, arp,oinil~ PEJ..T, .e;ofL, wet

''---------------------·-----f-···~-+------1 llOl: i!ig Tel:mbu1t.ed i:it. lR fpf't.

·--------.. ---.-------

File No. E 2204-MI

30 November 1964

--j-,.-+---··~:!5~ S11rf.,~1t ~~i:~n"'"'. ~07 b•r.k hroi.m to black, o~~•nt~ PEAT,

v~r.y i:.oft, .,...e~

'ft•~ l.o<.ac!on

'·~rl•

Gr.11y S~ndy Cl.Jl.Y, soft, ~et

Becoming liCi!f, d~nse CU..Y with silt ani:l .1111nd

J1.row11 51lty fine- SAND, ff.mt, C111rni:1A, 1110Lst

Bo:t:ing. T.erm:l.n~tl'."d At 2.3 fe?"'L

LOG OF TEST BOJllMC NO. 88

.... ,. ~•T ~\n~TI

"•"'\" (.""'~" ~·'·' ; ~" ~,

1 ... •••••

~., ~O!H.IU

n,.,,.,\" '"'·"""' '· c. '· " "" ~·

CL1t. Surfnce - Elev. 610 O·f--i-..----f-~--=:::_:::::c:_::::o__::::_:_:_:_--"-'"---------jf---j-·-·-

~ .J D11rk brown t.o bli:ick tirganic PEAT, vt'ry i, • .111tift., wet.

.1 . ~ ·10. ~ : : . : . : '

·, .. ··."·

Blu~-gray Silty CI.J\Y, we:i::, l!lofL

Blllti- gr11y S11nd-SILT, weL, m~cllum d~nell':

Llght. hrown Sili::y flne SARil, v~ry firm, dense, mo!.sr.

'----'--'--'-~------------.L--'-----1


105

., ., I· ,.

File No. E 2204-MI

30 November 1964

f'<••• , ...•

.10.

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~-~------------··----.,--~-.,. ___ , .. lo.•••••

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=='-'-"="-""'Ml_•_---+-- _, __ ~ C.:0111~1"ctC'd 5/::l~cly FILI..

W'-"4--···--------D~ptll (1f f.x1.:~Vtotiu11 l.1;11 l>r.nd Atei:1~-gr .. y

l>l'.l)Y'n Sil{y CIJl.Y, ii.ti.ff, 111~111.l.h~ dt-!1151"

Browll S1.lty 5Atill, firm. Lft!rl!OC', m.oLst

f'<>ring Tl:'rr11ln.iLerJ i:1t. lR f.cl!-t

Figure No. 36.-LOG

17. '}

~.--···-

OF TEST BORING

106

NO. 89.

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Appendix C

Recommended Grading Specificati.ons

Guide Specifications for Base Rock Under Concrete Slabs

.·.;

.. :.·,

'.··


RECOMMENDED GRADING SPECIFICATIONS

for

WESTBOROUGH

South San Francisco, California

1.1 General Description

1.11 These specifications have been prepared for grading and site development of Westborough, South San Francisco, California. Gribaldo, Jacobs, Jones and Associates, hereinafter described as the Soil Engineer, should be consulted prior to any work connected with site development to insure compliance with these specifications. The Grading Contractor must be made aware of the existence of these specifications.

1.12 This item shall consist of all clearing and grubbing, preparation of land to be filled, installation of subdrains, filling of the land, spreading, compaction and control of -the fill, and all subsidiary work necessary to complete the grading of the filled areas to conform with the lines, grades and slopes as shown on the accepted plans.

1.13 In the event that any unusual conditions, not covered by these specifications, are encountered during grading operations, the Soil Engineer shall be immediately notified for directions.

2.1 Tests

2.11 The standard test used to define maximum densities of all compaction work shall be the ASTM Test Procedure No. Dl557-58T. All densities shall be expressed as a relative compaction in terms of the maximum density obtained in the laboratory by the foregoing standard procedure.

109

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1.• '·' r I I

I

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•· i

1

I·

i I I i

"·-·-~~~~------------------


3.1 Clearing, Grubbing, and Preparing Areas to be Filled

3.11 All timber, logs, trees, brush, abandoned buildings, debris, and other rubbish shall be removed, piled or burned or otherwise disposed of so as to leave the areas that have been disturbed with a neat and finished appearance free from unsightly debris. No burning shall be permitted in the area to be filled.

3.12 All loose soil and vegetable matter shall be removed from the surface upon which t.he fill is to be placed, and the surface shall then be plowed or scarified to a depth of at least 6 inches, and until the surface is free from ruts, hummocks or other uneven features which would tend to prevent uniform compaction by the equipment to be used.

3.13 The original ground upon which the fill is to be placed shall be plowed or scarified deeply, and where the slope ratio of the original ground is steeper than 6 horizontal to 1 vertical, the bank shall be stepped or benched. At the toes of the major canyon fills and on any side-slope fills, the base key shall be at least 20 feet in width, cut into firm natural ground, and sloped back into the hillside at a gradient of not less than 2 percent. Subsequent keys should be placed at vertical heights of not more than 15 feet, and shall have a width of not less than 10 feet. Ground.slopes which are flatter than 6 to 1 shall be benched when considered necessary by the Soil Engineer.

3.14 After the foundation for the fill has been cleared, plowed or scarified, it shall be disced or bladed until it is uniform and free from large clods, brought to the proper moisture content by adding water or aerating, and compacted to a relative compaction of not less than 90 percent.

3.15 Loose soil removed in accordance with Paragraph 3.12, if free of vegetable matter and other deleterious material may be incorporated in compacted fill.

4.1 Subdrain Installation

4.11 Provide and install perforated asbestos-cement ~ipe, perforated bituminous-fibre pipe, perforated metal pipe, and filter mater.ial for subdrains, as shown on the plans

110

I

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I· I I

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1

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-I '


or as directed by the Soil Engineer and as specified in Section 68 of the Standard Specifications, January 1960, of the State of California, Department of Public Works, Division of Highways, except as modified in the following paragraphs.

4.12 Perforated asbestos-cement pipe or bituminous-fibre pipe will not be permitted either where the subgrade soils are compressible or where the depth of overburden soil exceeds 50 feet. Use of these materials will be permitted only on written authorization of the Soil Engineer.

4.13 Clay· drain tile, concrete drain tile, and perforated clay pipe will not be permitted. Use no wyes, elbows, tees, or other joints of these materials.

4.14 Use Type B filter material, unless otherwise permitted by written authorization of the Soil Engineer. Delete requirement of.State Specifications for quality testing using Los Angeles rattler or sand equivalent tests.

4.15 Unless directed otherwise, use pipes not less than 4 inches in diameter for laterals up to 50 feet in length. Use pipes not less than 6 inches in diameter for laterals greater than 50 feet in length.

. 4.16 Excavate trenc'h to width not less than 1 foot plus outside diameter or pipe, and to a gradient of not less than 1.5 percent. Bed the pipe on 6 inches of filter material, and install at such depth that there is not less

·than 2 feet of filter material above the crown of the pipe. Cover the filter material full trench width with 1 layer of building paper when the overlying soils will be predominantly clayey, or as directed by the Soil Engineer.

.5.1 Materials

5.11 The materials for the fill shall be approved by the Soil Engineer before commencement of grading operations. Any imported material must be approved before being brought to the site. The materials used shall be free of vegetable matter and other deleterious substances. Stones up to 2 feet in diameter will be permitted in mass fills provided they are not placed within 5 feet of finished grade and

111

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Fi::._e No- E2204-Ml 30 ll<'":'V...mi>e:::" 1964

th-".t :nesting is avoided. Stones larger than 2 feet in diarr:e~er wi.11 not be permitted unless approved in writing by :tbe Soil Engineer.

5. J2 ¥..aterials on the site are suitable for use as fill si:C"::ij ect to the following limitations: ·

5. l22 The serpentine clays of Zone I shall not be used· iu £i11 unless they are thoroughly mixed with other nonse.::i:i.en.tinized soil. No such soil mixture shall contain mc::r~ t:.han 20 percent by weight of serpentine.

5. l22 !io serpentine clay or soil with a high serpentine cc:;::i.tent sh.all be placed within 5 -feet of finished grade or c£ t.be surface of any fill slope. ·

5.l23 Peat, saturated clays, and similar soils defined as soch at the sole discretion of the Soil Engineer, s:--,,ll c.e spread in l_ayers not more than 6 inches in thick-

-ness ~ sandwiched between 2-foot thick layers of the mater-::...al.s fr= either Zone I or Zone III, and shall not be p:_aced -.,;ri_t:hin 5 feet of finished grade or of the surface o::: =-Y fill slope.

5 _ l3 The Contractor shall notify the Soil Engineer at 12a.s:i: 4 working days in advance of his intention to impa- ~ soil or filter gravel from any source outside Westb.::;r=p, and shall permit the Soil Engineer to sample as oacessary for the purpose of making acceptance tests to p=c-ovE the qualities of these -materials. The Contractor s:'<all be :responsible for all costs incurred in sampling t.;.st:.ing, analyzing, and otherwise determining the ade- ' ~ of :t:he materials for use on the site. The work sh,,,_ll be performed by the Soil Engineer chosen by the G~r aud the report by the Soil Engineer on the ade~::iacy' of the material shall be final and binding.

c: ?lacing, Spreading and Compacting Fill Material

:i . :__2 The selected fill material shall be placed in layers -,.: '~h when compacted shall not exceed 6 inches in thick-=c,~,3. &ch layer shall be spread evenly and shall be :::::tl::::.::'."a-.;.ghly blade mixed during the spreading to insure uni·=::::::mi=y of material in each layer.

i ., Iii

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• • II

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•• ••

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6.12 When fill material includes rock, no large rocks will be allowed to nest and all voids must be carefully filled with small stories or earth and properly compacted. No large rocks will be permitted closer than 5 feet below the finished grade.

6.13 When the moisture content of the fill material is below that specified by the Soil Engineer, water shall be added until the moisture content is as specified to assure thorough-bonding during the compacting process. When the moisture content of the fill material is above that specified by the Soil Engineer,· the fill material shall be aerated by blading or other satisfactory methods until the moisture content is as specified.

6.14 After each layer has been placed, mixed and spread evenly, it shall be thoroughly compacted to a relative compaction of not less than 90 percent.

6.15 Compaction shall be by sheepsfoot rollers, multiplewheel pneumatic-tired rollers or other types of acceptable compacting rollers. Rollers shall be of such design that they will be able to compact the fill to the specified density. Rolling shall be accomplished while the fill material is within the specified moisture content range. Rolling of each layer shall be continuous over its entire area and the roller shall make sufficient trips to insure that the required density has been obtained.

6.16 Fill slopes shall be compacted by means of sheepsfoot rollers or other.suitable equipment. Compacting operations shall be continued until the slopes are stable. While no appreciable amount of loose soil will be permitted on the slopes, compaction shall not be so dense as to prohibit planting. Compacting of the slopes may be done progressively in increments of 3 to 5 feet in fill height or after the fill is brought to its total height.

6.17 Field density tests shall be made by the Soil Engineer of each compacted layer. At least one test shall be made for each 1,000 cubic yard, or fractions thereof, placed with a minimum of two tests per layer in isolated areas. Where sheepsfoot rollers are used, the soil may be disturbed to a depth of several inches. Density tests shall be taken in cqmpacted material below the disturbed surface. When these tests indicate that the compaction of any layer of fill, or portion thereof, is below the re-

113


quired 90 percent relative compaction, the particular layer or portion shall be reworked until the required compaction has been obtained.

6.18 The fill operation shall be continued in 6-inch compacted layers, as specified above, until the fill has been brought to the finished slopes and graded as shown on the accepted plans.

6.19 All earth moving and working operations shall be controlled to prevent water from running into excavated areas. All water shall be promptly removed and the site kept dry.

7.1 Supervision

.. 7.11 Inspection by the Soil Engineer shall be made during filling and compacting operations so that he can certify that the fill was made in accordance with accepted specifications. Inspection by the Soil Engineer shall also be made during the installation of all subdrain facilities.

8.1 Seasonal Limits

8.11 No fill material shall be placed, spread or rolled during unfavorable weather conditions. When the work is interrupted by heavy rain, fill operations shall not be resumed unt,il field tests by the Soil Engineer indicate that the moisture content and density of the fill are as pr·eviously specified.

9.1 Wells

9.11 Where encountered, wells shall either be backfilled with filter gravel, or capped with concrete at least 3 feet thick and of a diameter 2 feet greater than the diameter of the well. If backfilled with gravel, the well shall be connected by a subdrain lateral to the nearest convenient subdrain main outfall. Concrete used in capping shall have a minimum 28-day compressive strength of 2,500 p.s.i.

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GUIDE SPECIFICATIONS FOR BASE ROCK UNDER CONCRETE SLABS

Definition

Graded gravel or crushed rock for use under concrete floor slabs on grade shall consist of a minimum thickness of mineral aggregate placed in accordance with these specifications and in conformity with the dimensions shown on the plans. The minimum thickness is specified in the accompanying report.

Material

The mineral aggregate for use under floor slabs shall consist of broken stone, crushed or uncrushed gravel, quarry waste or a combination thereof. The aggregate shall be free from adobe, vegetable matter, loam, volcanic tuff and other deleterious substances. It shall be of such quality that the absorption of water in a saturated dry condition does not exceed 3% of the oven dry weight of the sample.

Grading

The mineral aggregate shall be of such size that the percentage composition by dry weight as determined by laboratory sieves (U.S. Sieves) will conform to the following grading:

Sieve Size Percentage Passing Sieve

1" 100 3/4" 90-100 No. 4 10-35 No. 30 2-10 No. 200 0-2

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Placing

Subgrade, upon which gravel or crushed rack is to be placed, shall be prepared by removing grass and roots. Where loose topsoil is present, it should be tamped or rolled, Density and moisture content requirements will be specified by the Soil.Engineer.

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Report on Earthquake Hazard by

Dr. Frank W, Atchley, Consultiri.g Geologist

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EARTHQUAKE HAZARD

AT THE

PROPOSED SITE OF WEST PARK UNITS 1 AND 2,

WESTBOROUGH

San Mateo County, California

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EARTHQUAKE HAZARD

Introduction


I have been asked to comment on the earthquake hazard at

the proposed site for West Park Units 1 and 2, Westborough,

South San Francisco, San Mateo County, California. I have

discussed the hazard briefly with the owner-developer and

attended. a City Council meeting in South San Francisco, on

May 27, 1964, to answer questions on his behalf. No ques-

tions were asked.

A pe·l'."spective view of the proposed subdivision is important,

The proposed site essentially straddles the main shear zone

of the San Andreas fault, and crosses the line or rupture

where movement took place in 1906._ Grading plans call for

substantial remoulding of the natural terrain, with retreat

of the canyon sidewalls by excavation at slopes of approxi.,

mately 2:1 (horizontal to vertical). and placement of up to

70 feet of compacted fill in a narrow valley directly over

existing earthquake sag ponds. Proposed structures include

one- and two-story "cluster" dwellings, multi-story apart

ments, school buildings, and o shopping center. The pro-

posed school site is roughly in the center of the valley,

more-or-less over the area of deepest fill.

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The San Andreas fault is recogni.zed as one of the most ac·-

tive faults in the entire United States, if not the North

American continent. It has generated mlIIlerous earthquakes

throughout its length and has produced three major earth

quakes in the Bay Area in historic time.

In contemplating the above situation, I end up in a quandry.

The presence of earthquake hazard is obvious, but what kind

of hazard and how much hazard, calamitous or inconsequen,

tial? In short, I find myself unable to identify any quan-

titative significance of earthquake hazard with current

knowledge on the subject. Science has no clear definition

of earchquake hazard, and no standard, scale, or frame of

reference to describe and compare earthquake hazard. The

problem is compounded with difficult semantics, and indi-

vidual prejudice and emotion. No one.seems to know, or

care, wh;it can or should he done about earthquake hazard,

or who is respons:i.ble for decisions that involve gross haz

ard of community property damage and loss of life.

To objectively discuss earthquake hazard, I find it neces-

sary to explain my personal feelings and philosophy on the

subject and to review current understanding of earthquakes

and earthquake damage causes. To present any quantitative

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assessment of magnitude of earthquake hazard, I find it

necessary to develop a new basic framework, or scalar sys

tem, for assessing the various determinants of earthquake

hazard, where the sum of values represents total native

hazard at a particular site. The range of values for each

hazard determinant is an arbitrary progressive scale from

extremes of minimum to maximurn hazard known to science.

This rating system is described in the report and used to

identify the earthquake hazard at the proposed subdivision

site.

Qualifications

I would like to establish my qualifications for evaluating

earthquake hazard by submitting the attached "Professional

B-.cochure" and noting that my experience includes consulta-

tion on the earthquake hazard at the Stanford Linear Accel-

era tor Site for the Atomic Energy Cmnmission, on proposed

school sites in the Woodside area (in the San Andreas Fault

Zone), and on numerous dams and tunnels in and around the

Bay Area. I have visited the West Park {Westborough) area

several times during past years and am generally familiar

with the proposed development.

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Personal Philosophy

A major earthquake and its related phenomena of tidal

waves, landslides, fires, etc. can be truly catastrophic

in terms of property damage and loss of life. Earthquake

hazard, therefore, can be a real frightening danger to

the works of man, to the individual, and to the general

public. However, degree of earthquake hazard depends on

special circumstances which can be analyzed. Viewed ob

jectively, earthquake hazard, like any hazard, is but one

of many considerations that bear on project feasibility.

If the hazard is excessive and cannot be physically or eco

nomically resolved to an acceptable risk, then the project

simply is not feasible. The crux of the problem is deter

mining whether the hazard is excessive or not, what level

of risk i.s acceptable, and who is responsible for making

the final decisions.

In these regards, I want to clarify my responsibility as

a Consulting Geologist. I feel it is my responsibility,

as well as that of my profession, to understand, recognize,

and identify earthquake hazard and all its variables and

ramifications. We are responsible for failure to recog-

nize the hazard and for failure to identify that hazard

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to others, but it is not our right or responsibility to

say what can or cannot be done about it. Once identified,

I feel it is the responsibility of the planner and engi-

neer, in conjunction with the owner-client, to resolve

and minimize the hazard through project planning and spe-

cific structure design. The final responsibility rests

with the owner-client and public agencies to analyze. the

moral, legal, and economic aspects of the risk involved

and decide whether or not it is acceptable.

I personally regard earthquake hazard as a risk of life,

more-or-less as commercial aviation. Airliners crash,

destroy property, and kill people, but we don't stop fly-

ing for fear of c.rashes. We determine the causes of the

crashes, and how, when, where, and why they are most like

ly to occur, then try to eliminate them by avoiding past

mistakes and building better and safer airplanes. The

same approach should hold for earthquakes and earthquake

hazard.

In short, I feel that progress requires acceptance of

earthquake hazard, with realization that something can be

done to minimize the danger. We cannot prevent or predict

the occurrence of an earthquake, but the hazard can be

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Flle No. E2204-Ml 3(J November 1964

171tnirnized by avoiding and/ or correcting unfavorable sites

with proper development planning and proper structure de-

sign.

Earthquakes

Earthquakes ar:e simply ground vibrations resulting from

the sudden rupture and release of strain energy that has

accumulated in the earth's crust. The rupture plane is

called a "fault;" the place of initial rupture is called

the "focus;" and the point on the earth 1 s surface di.rect-

J above the focus is called the "epicenter." .y The size,

~ "rnagnitude" of an earthquake is an instrumentally deo.c

rived quantity that relates to the total energy of the

earthquake. The affects of an earthquake, after it oc

curs, are described in terms of "intensity" according to

an m:bitrary scale of destructiveness based on sensual

perception and structural damage. The ternl earthquake

intensity, unfortunately, has been used loosely to denote

severity of shaking and degree of hazard. This is erron

eous. Earthquake int~·nsity is assessed largely on the

basJ.1> of structure damage, which depends on structure type,

age, and design, as well as the severity of ground shaking.

}.>'or tnstance, a city of old brick buildings might experience

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major damage in a minor earthquake, while a city of new

steel-concrete buildings might experience minor damage in

a major earthquake. In the former case, the earthquake

intensity would have a high rating; and. in the latter case

a low rating.

Earthquake vibrations are transmitted through the earth's

crust in two principal types of energy waves: a primary,

or thrust shock wave, that travels more-or-less in a direc

tion parallel to the direction of fault movement; and sec

ondary, transverse waves that travel generally at right

angles to the fault plane. In both wave types, the wave

velocity, amplitude, attenuation, etc., depend on the be

havior and nature of the materials being transversed.

Dense crystalline rock typically transmits high speed, low

amplitude waves for great distances, whereas soft material

transmits slow speed, large amplitude waves for short dis

tances. Primary shock waves account for uprooted trees,

tombstones toppled over, and buildings knocked off their

foundations, all in the same direction. Secondary trans-

verse waves result in repeated pulsations and vibration

resonance which shake buildings apart.

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Earthquakes are classified in accordance with depth of

origin as shallow focus (Oto 40 miles), intermediate

focus (40 to 200 miles), and deep focus (over 200 miles).

Shallow focus earthquakes are most abundant.

Earthquakes are believed to be caused by slow movements

within the earth's crust which result in gradual accumu-

lat ion of elastic strain energy until rock strength is '

exceeded, then sudden release of stored energy by fault

rupture, followed by gradual accumulation of strain again,

more-or-less in a cyclical pattern.

The differential displacement that takes place during

fault movement can be at any angle or direction from ver

tical to horizontal. The distance, or length of the rup

ture can vary greatly, with longest break on record being

some 270 miles on t;he San Andreas fault in 1906. The

amount of displacem~nt generally varies from a few feet

to several .tens of fe~t, ·with largest displacement 0n rec

ord being 47 feet in Yakutat Bay, Alaska, in 1899. .,

Earthquakes can occur anywhere in the world, although

they are centered principally in local, restricted belts

and zones around, the globe. Best known.of.these "earth

quake belts" is the Circum~Pacific belt which more-or-

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less surrounds and borders the Pacific Ocean, and the

Mediterranean-Himalayan belt which extends from Portugal

eastward into India. The West Coast of the United States

lies within the Circum-Pacific belt, particularly Nevada

and California. This region has experienced over 100,000

earthquakes since early 1800's, including some 50 shocks

of damaging magnitude. Statistically, this means that

damaging earthquakes occur in California and Nevada once

every 4 to 5 years.

Earthquake Damage

Earthquake damage is most capricious and depends heavily

on men's own actions of site selection and structure de-

sign. By disregarding man's actions, the problem narrows

down.to the basic cause of damage: ground behavior to

earthquake forces. This behavior produces primary and

secondary damage, Primary damage is that damage imparted

direct to structures from ground response to earthquake

forces of shear, shock, and vibration, while secondary

damage results from earthquake triggered phenomena, such

as landslides, subsidence, flooding, tidal waves, and

fire.

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Primary damage from ground behavior, or course, depends

on the peculiarities of individual earthquakes as to total

energy, depth of origin, suddenness of rupture, direction

of movement, etc., as well as for the peculiarities of a

given site with regard to topography, soil and rock condi

tions, and geologic structure.

In resolving the variables of ground behavior, we can dis

regard earthquake peculiarities and make prognosis of

"probable ground behavior" based on empirical experience.

On this basis, we can group various categories of geologic

conditions under general. broad classifications of: 1)

Rock foundation; 2) Semi-consolidated rock .. or firm soil;

and 3) Unconsolidated or loose soil. These three ground

classes possess more-or-less a range in degree of hazard

in their response to earthquake forces of shear, shock,

and vibration, as indicated in the following tabulation.

The degree of hazard in each class is relat~d to the mate

rial_ depth, at"eal extent,. and whether' dry or water satu

rated.

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Primary Ground Motion Hazard to


Earthquake.Forces

Ground Class Differential Thrust Vibration Shear Shock

Rock foundation Maximum Maximum Minimum Semi-consolidated Intermediate Intermediate Intermediate

rock or firm soil

Loose soil, sand, Minimum Minimum MaximUIIl silt, mud, etc.

The force of differential shear results from either ver

tical or horizontal surface displacement by fault move

ment. Maximum damage hazard therefrom depends on site or

structure location across the rupture plane or immediate

ly within the zone of deformation where the fault movement

takes place. Differential shear occurs only when fault

rupture extends to the surface.

Thrust shock comes from the sudden explosive-like release

of energy from fault rupture. Maximum damage from thrust

shock occurs in areas immediately contiguous to the line

of surface fault rupture. Thrust shock can also originate

from deep-seated earthquakes and can be directed vertical

ly upward.

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Vibration damage is present in nearly all earthquakes and

is responsible for the major share of direct earthquake

damage. Ground response to earthquake vibrations depends

solely on geologic conditions and on the influence of sea

sonal climatic change on those conditions. Maximum damage

almost always occurs on deep, unconsolidated, well-satu

rated soil and loose fill. Such material effectively am

plifies and increases the size and severity of earthquake

vibrations.

Secondary damage from earthquake-triggered landslides,

tidal waves, fires, etc., often is more devastating than

primary damage. It has been estimated that 80% of the

damage loss during the 1906 San Francisco Quake was

caused by fire and only 20% from. primary damage. Large

scale landsliding produced the major proportion of damage

in the recent "Good Friday" disaster in Alaska. The cata

strophic damage from tidal waves needs no discussion.

Earthquake subsidence can and has reversed the course of

rivers, submerged valleys, and drowned cities, with re

sulting major damage. Secondary earthquake damage hazard

depends largely on local geologic conditions. Location

on or near hills or slopes having known history of land

sliding is particularly hazardous. Low lying marsh land,

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subject to flooding from local settlement or from regional

subsidence, is hazardous. Areas of filled, reclaimed

ground are particularly susceptible to heaving, lurching,

and severe vibration.

Earthquake Hazard

Evaluation of earthquake hazard is an extremely compli

cated subject and most opinions thereon are likely to be

biased by personality, experience, point of view, or lack

of knowledge. We have no good definition of earthquake

hazard and there is difficulty in classifying its many

variables into quantitative terms. We have the term II mag-

nitude" to describe the size of an earthquake, and a scale

of "intensity" to describe the destructiveness of an earth

quake, but have no scale or method of assessing and classi

fying earthquake hazard. An approach to the problem is

suggested in the following paragraphs.

Earthquake hazard is generally thought of as the chance,

or risk, or property damage and loss of life that would

result from a major earthquake centered at or near a par

ticular site. The definition is adequate for discussion,

but offers nothing specific or informative on the nature

133


of the risks. I propose that earthquake hazard be identi

fied as a fivefold risk of property damage and loss of

life that comes from: l) earthquake frequency; 2) geo-'

graphic location; .3) local geologic conditions; 4) soil

conditions; and 5) structure design:· Each of these haz-

ards is distinct and can-be assigned an arbitrary hazard

factor from 0 to 10, depending on degree of seriousness.

The summation of the five hazard factors gives a numeri

cal rating of total earthquake hazard. Maxilllum total haz

ard would have a rating of 50, while minimum hazard would ..

have a rating of zero. A hazard rating of 50 would pre-

vail in an area holding imminent potentiai for a major

earthquake (10), plus location at or near a probab~e

earthquake epicenter (10), plus unfavorable local geologic

conditions (10), unfavorable soil conditions (10), and an

unsafe, unfavorable old structure (10). A minimum rating

of zero would prevail in an area that has never experi

enced an earthquake (O), plus location at· great distance

from nearest known epicenter (0), plus favorable geologic

conditions (0), plus favorable soil conditions (O), plus

a safe, well-designed structure (O),

Earthquake Frequency: Assessing the earthquake frequency

hazard involves analysis of the historical, seismic, and

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geological record of past earthquake activity in a given

region. Conclusions on the probability of future earth

quakes are predicated generally on the assumption that

future earthquake activity will resemble past activity,

more-or-less in accordance with the theory of cyclical

occurrence of earthquakes. Where earthquakes are few

and far between, the frequency hazard is uncertain, but

can be assessed arbitrarily between 0 and 5, depending

on regional geology. Where earthquakes are reasonably

common, the rating would be between 5 and 10, depending

on the particular situation. An area like the Bay Area,

with its history of major earthquakes, would clearly

hold maximum frequency hazard rating of 10. (See later

discussion on Earthquake History of the Bay Area).

Geographic Location: The geographic location, or prox

imity factor, of earthquake hazard depends on gradual

energy attenuation away from the earthquake source or

epicenter, with degree of hazard generally decreasing

with distance. However, earthquake energy is so great

and the rate of attenuation is so small that no signifi

cant difference in hazard occurs within geographic dis

tances of about 25 miles. That is to say, considerable

difference in hazard would exist between 25 and 200

135


miles from an epicenter, but not necessarily between 5,

15 or 25 miles. This means, in effect, that local geo

logic conditions and specific soil conditions (factors

3 and 4) are the principal determinants of earthquake

hazard in any given local area. With equal site condi

tions, a 10-mile change in location might offer no

change in hazard with respect to factors 1 and 2, where

as a 100-foot change to take advantage of new, favorable

geologic or soil conditions might drastically reduce the

hazard. The hazard of geographic location is rated arbi

trarily on the basis of the distance of the particular

site, in multiples of 25 miles from known, active earth

quake-producing faults, areas, belts, or zones 'of high

seismic activity. For example, the north central areas

of the United States would have a distance hazard rating

of zero, since the area has never experienced an earth

quake in recorded history; the Southeast United States

would be rated perhaps 2 or 3; the Utah area at about.5 ' '

or 6; and the Southern California area between 8 and 10.

The entire Bay Area, with its numerous active fault sys

tems~ would hold maximum geographic location hazard of

10.

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Local Geologic Conditions: Local geologic conditions con

stitute by far the most capricious aspect of earthquake

hazard. Distinct, sharp, local difference in hazard is

the general rule, depending on particular topography, geo

logic. structure and rock condition. Local geologic hazard

varies from a rating of zero for massive, unfractured crys-

talline rock terrain haviJ:J,g no danger of landsliding or

flooding, up to a maximum of 10 in terrain subject to land-

' sliding, flooding, shear dislocation, ground shifting, or

large amplitude vibrations. The Bay Area, with its vari

ety of geologic conditions, clearly has variable site haz-'

ard ratings, ranging from perhaps 2 to 3 to a maximum of

10. Sound,massive rock foundations, as in some of the

foothills, would hold a.geologic hazard rating of perhaps

2 to 5, while a rating of 8 to 10 would apply at a site

having steep topography associated with unstable rock con

ditions.

Local Soil Conditions: Local soil conditions, like struc

ture design, are amenable to engineering analysis. Through

drilling and laboratory study, the soil conditions at a

particular site can be assessed with regard to earthquake

behavior. The factors that detennine earthquake behavior

include soil depth, degree of consolidation, density, amount

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of saturation and grain~size distribution. Mini.mum haz

ard comes from shallow, well-drained consolidated soils, --

while maximum hazard is associated with deep, water-satu-' rated deposits of soft unconsolidated materials. Often

unfavorable natural soils can be improved by proper site

development techniques, such as base preparation, drain

age, and compaction. In fact, controlled, engineered

fills, built to modern standards on firm subbase founda

tion can be vastly_ superior to loose natural soils with

regard to eaithquake-behavior. Soil conditions in the

Bay Area range from extremes of zero for exposed rock

footings to a maximum of 10 in the reclaimed marsh land

surrounding the Bay.

Structure Design: Structure hazard is a function of building design, materials, and construction, as well as

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building size, shape; height, and age. Empirical expert-'

ence'has clearly shown that minimum structure hazard of

zero is afforded in well-engineered, steel reinforced,

concrete buildings. Maximum structure hazard ~ating of

10 is found in old, unreinforced masonry buildings, with

intermediate ratings of 4 to 6 found in wooden frame

structures-. Structure hazard includes an arbitrary con

sideration of dwelling density and the resulting danger

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of major fire. For example, isolated wood frame struc

tures on individual lots afford a lower structure hazard

rating than contiguous wood frame structures, as in some

tenement districts.

The foregoing five factor hazard rating system is based

on earthquake frequency, geographic location, geologic

conditions, soil conditions and structure design. As de

fined, the "F.L.G.S.S." rating system gives a reasonable

picture of the variable nature of earthquake hazard. It

establishes a relative numerical scale of from 0 to 50

for total earthquake hazard in existing structures at any

locality. It includes the "unavoidable" risks of earth

quake frequency and geographic location, and the "avoid

able" risks of unfavorable geologic conditions, unfavor

able soil conditions, and unfavorable structure design.

By disregarding the factor of structural design, it pro

vides an arbitrary quantitative scale of earthquake haz

ard at undeveloped natural sites. With earthquake fre

quency and geographic location fixed and unavoidable, the

cr.itical importance of local geology and specific soil

conditions becomes apparent. By assuming adequate struc

tural safety, the two main detenninants of earthquake haz

ard rests on local geology and specific soil conditions

139


of each particular structure site.

Evaluation of Earthquake Hazard

As indicated above, earthquake hazard encompasses factors

of time and location with regard to seismic activity, spe

cific site conditions, and specific structure design.

These factors, respectively, are basic subjects in the

fields of Seismology, Geology, and Engineering and are

best evaluated by specialists in their fields. As a geol

ogist, I am generally familiar with both seismology and

engineering, but am not qualified to be specific in eithe.r

fi.eld.

In this particular case, I am confident with regard to

seismic conditions in the project area for I have had the

opportunity of working with Dr. Perry Byerly, Seismolo

gist, University of California, Berkeley, in the evalua

tion of earthquake hazard at the Stanford Two-Mile Linear

Accelerator, near Palo Alto, California. This work in

volved exhaustive study of the seismic and earthquake his

tory of the Bay Area.

As noted previously, I feel that the major problem in

evaluating earthquake hazard is establishing a common

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frame of reference for discussion, comparison, and analy

sis. To this end, I state that earthquake hazard con

sists of unavoidable risks of earthquake frequency and

geographic location, and of avoidable risks of local.

geology, specific soil conditions, and particular struc

ture design. I stress that it is the responsibility of

the profession of Engineering Geology to fully identify

unfavorable site conditions with respect to earthquake

hazard, but that final assessment of the hazard is the

joint responsibility of the engineer, client, and public

agencies with regard to the adequacy of design measures

in resolving the danger to an acceptable level of risk.

Earthquake History in the Bay Area

In brief .review, the Bay Area is a region of an0malous,

almost constant minor seismic activity, major earthquakes,

numerous active fault systems. On the south side of the

Bay, running diagonally across the Peninsula, is the

great linear rift of the San Andreas fault system. On

the east side of the Bay, bordering and cutting through·

the hills, are numerous branching faults of the Calaveras

and Ha:Yward systems. Other major, less active faults un

derlie the Bay itself. These fault systems are shown on

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the following map of earthquake epicenters in the Bay

Area.

The historic record shows the Bay Area has an unparallel

ed seismic history. It has witnessed five major earth

quakes during the years 1836, 1838, 1865, 1868, 1906, and

numerous minor earthquakes, as near Niles in 1933, near

Berkeley in 1937, and near Daly City in 1957. Three of

the major earthquakes originated on the San Andreas fault,

1838, 1865 and 1906, and two on the Hayward fault, 1836

and 1868. Surface rupture accompanied four of the fault

movements, in 1838 and 1906 on the San Andreas fault, and

in 1835 and 1868 on the Hayward fault.

When compared to other areas, earthquake history of the

. Bay Area looms highly significant. For instance, no

other local area in the entire United States has ever ex-

perienced more than one major earthquake or more than one

surface rupture in historic time. The Bay Area has ex

perienced five major earthquakes and four surface ruptures.

The seismic activity of the Bay Area is illustrated on

the Epicenter Map. This map covers only a limited time

span of 12 years, 1930 to 1941 and 1947 to 1948, but clear

ly shows that the bulk of activity is centered in the East

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EPICENTER MAP

File No. E2204~Ml

30 November 1964

SAN FRANCISCO BAY REGION 1930 -1941 AND 1947- 1948

(.AFTER BYERLY )

EAllT~O\IJlll( lllTEll!fl1Tlj' •at: .. TlJll Tfipj 411

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Map shovs the principal fault systems ot the Bay Area (heavy black lines) and the epicenters that occurred during the periods 1930-19ltl and 19lt7-191t8. The intensity ot the various shocks is shovn by the epicenter sYlJlbols listed in the legend at the left ot the map.

143


Bay Hills in the Hayward, Mt. Hamilton, and Gilroy areas.

The San Andreas fault, in comparison, shows little or no

activity. The general quiescense of the San Andreas

fault has extended from the 1906 rupture to the present

date, and has led to the general belief that it has been

accumulating strain energy leading to another rupture

and another major earthquake. This idea is fostered by

survey results of work by the U.S. Coast and Geodetic

Survey showing that mountain peaks on opposite sides of

the San Andreas fault are drifting apart at an average

annual rate of about 2 inches per year. This rate of

movement has been confirmed by repeated survey measure

ments. The movement is taking place between points 40

to 50 miles apart, but whether it is distributed over

this entire distance or concentrated in local zones of

weakness in unknown. Apparently the movement has been

continuous since 1906, and if true, it means that the

Bay Area has accumulated some 9 to 10 feet of total

strain.**

**Further discussion of seismic activity and strain accumulation is included in my report on the Stanford Linear Accelerator, entitled: Geologic Investigation of the Stanford Two-Mile Linear Accelerator; prepared for U.S. Atomic Energy Commission; W. W. Hansen Laboratory of Physics, Stanford University, 1960.

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File No. E2204-Ml 30 November 19~4

As noted previously, analysis of earthquake frequency and

geographic location hazard is based on the historical,

seismic, and geologic record, plus theory of cyclical oc

currence of earthquakes and the assumption that future

earthquake activity will resemble past activity. In this

regard it is pertinent that Dr. Perry Byerly, Seismolo

gist, University of California has stated that the Bay

Area is the most seismic area in California. Dr. Charles

F. Richter, Seismologist, California Institute of Technol-

~ ogy, has described the Bay Area as th,e most hazardous

I earthquake area in the entire United States. !,

• Considering everything, I feel that the earthquake fre

quency hazard of the Bay Area warrants maxim.um hazard rat

ing of 10 on the F.L:G.S. rating scale. Because of its

numerous active fault systems, all capable of producing a

major. earthquake, I feel that the geographic location haz

ard also warrants maximt.un hazard rating of 10. These

maximum hazard ratings apply to all of the general Bay

Area and point up the great importance of the avoidable

factors of earthquake hazard--local geology, soil condi-

tions, and structure design--in minimizing the earthquake

risk.

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The seriousness of the general hazard in the Bay Area is

exemplified in the great "San Francisco'' earthquake of

1906. Rated at Richter magnitude of 8.3, and accompanied

by surface fault rupture of some 270 miles, it was one· of

the largest earthqua,kes ever to strike California. The

fault movement was essentially horizontal in direction,

with shear displacement on the order of 8 to 10 feet where

the rupture passed through the proposed site.

The 1906 earthquake provides clear example of variable

ground response to forces of shear, shock, and vibration.

It showed direct correlation between varying vibration

damage with the character and type of structure founda

tions, and that maximum thrust shock typically occurs in

the immediate fault zone along the line of rupture. It

also showed that ground response to differential fault ' shear varies from a relatively clean sharp break in areas

of rock, to a wide zone of flexure- in areas of -deep soil,

alluvium, or fill. This difference in ground behavior to

earthquake forces is well documented in the literature.

Of pa:i:.ticular interest. is the very fact that the 1906 rup

ture passed under the old earth-fill Crystal Springs dam,

which did not fail but deformed with "plas'tic" drag .flex-

ure.

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Earthquake Hazard at the Proposed Site


The proposed development site essentially straddles the

main San Andreas fault and will involve hillside excava-

tion and placement of up to 70 feet of fill in a steep,

narrow canyon-like valley directly over existing earth

quake sag ponds. Such conditions raise pertinent ques

tions: ... What degree of earthquake hazard is involved'?

What specific hazards are present? And are the hazards

significantly different from those in areas farther away

from the fault?

In answering these questions, let me review briefly that

earthquake hazard includes any condition that poses dan

ger of primary or secondary earthquake damage and loss

of life, Primary damage comes from ground response to

earthquake forces of shear, shock, and vibration; secon

dary damage comes from earthquake-triggered phenomena as

landslides, flooding, fires, etc.

In this case, it is apparent that the proposed site holds

question of both primary and secondary damage hazard.

The primary damage hazard comes from the danger of fault

shear transecting the property, with accompanying drag de

formation, and from the danger of strong thrust shock.

147

File No. E2204-Ml 30 Novein.ber 1964

Primary damage hazard from ground vibration als.o is pre

sent, but appears to be less than at other plac·es in the

Bay Area. This is because the proposed, drained, com-; ..

pacted fill, placed over firm ground, will provide a.gen

erally safer foundation with respect to vibration danger

than reclaimed mud flats, or deep,water-saturated alluvium - "1 .

as elsewhere in the Bay Area.

The secondary damage hazard is the danger of earthquake

triggered landslides and slumps in the adjoining hillside ;

cuts. This hazard,_of course, depends upon specific rock,

slope, and soil conditions at each particular cut. Where ..

the slopes are gentle, rocky, and dry, there should be

little danger. But where the slopes are steep and under

lain by soft, wet, or clayey materials, as I understand ' "! .

they are locally on the west side of the valley, then rea-' sonably serious hazard of earthquake slope failure is pre-

sent.

The degree, or seriousness, of the combined hazards of

fault shear and thrust shock depend on s~ecific site loca

tion with respect to fault trace and origin of the earth

quake (whether deep-seated or shallow-focus origin). In

this case the proposed site essentially straddles a major

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active fault line having known history of major earth

quakes and surface rupture. It is clear, therefore,

that should another earthquake originate on this fault,

regardless of depth, that the site is certain to exper

ience strong thrust shock. If of shallow origin, and

accompanied by surface rupture, it is equally clear

that the site would be subjected to forces of fault

shear and ground dislocation. Just how the deep fill

. would respond to these forces is uncertain, and whether

underlying fault rupture would reach the surface or be

masked by plastic drag movement within the fill is un

known. Further, whether or not the fill would respond

to forces of shock and vibration with ground heaving,

lurching, and cracking, and/or settling is not predict

able, except that such behavior is more apt to occur in

areas of fill than in areas of rock.

The validity of stating that the proposed site straddles

the San Andreas fault deserves scrutiny. Actually, the

San Andreas "fault" is not a single fault, but a system

of numerous branching and coalescing fault planes to

gether forming a "rift" zone of weakness upwards to 1/2

mile or more in width. Fault ruptures have occurred

throughout this zone in geologic time and there is no

149


sure way of predicting where future fault ruptures will

occur. However, it is logical and reasonable that the

next coming rupture will occur at the place of known max

imum weakness; that is, in the same line and plane as the

1906 rupture. This is according to the axium ... "The

chain will break at its weakest link." Such reascming

is corroborated with regional geologic evidence of stream

deflection, topography, and erosion, showing that repeat

ed movements have taken place in a local main fault zone

within the greater-San Andreas rift width in recent.geo-'

logic time. This is verified by topographic lineament,

by old maps, of the 1906 Carnegie Earthquake Commission,

and by exposure of shear material in the canyon bottom

during excavating of the sag ponds.

Considering everything, I feel that the evidence and rea

soning clearly indicate that the proposed site possesses

serious earthquake hazard and warrants assessment of max-

imum geologic hazard rating of 10 on the F.L.G.S. rating

scale. The site does, in fact, cross the main San Andreas

fault line where future rupture, shear dislocation, and

strong thrust shock are most likely to occur. I feel that '

the unique earthquake history of the Bay Area, geologic

tpeory of cyclical origin of earthquakes, the assumption

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that future earthquake activity will resemble past activ

ity plus seismic records and U.S. Coast and Geodetic sur

vey evidence, all suggest that it is just a matter of time

until another major earthquake strikes in the Bay Area. I

feel there is no doubt that future earthquakes will origi

nate from movement on the San Andreas fault and that one

or more of these may be accompanied by surface rupture, as

in the past.

Soil Conditions at the site will consist of cut pads expos

ing rock and semi-consolidated rock materials and upwards

to 70 feet of compacted fill over firm ground. Subdrain

age within and beneath the fill is to be provided. Such

materials will provide far better foundation conditions

than reclaimed marsh land around the Bay with respect to

vibration hazard. But, as mentioned, their behavior to

shock and shear remains uncertain. Compared to rock, a

realistic soil hazard rating for the compacted fill would

be about 5.

The geologic hazard rating of 10 and soil hazard rating of

5 combines with the Bay Area frequency hazard rating of 10

and location hazard rating of 10 to give a total hazard

rating of 35, or about 87% of the maximum earthquake hazard

151


that an undeveloped site can possess. Such a rating

clearly dictates that extreme care must be exercised in

development planning and in se.lecting the structure type,

design and orientation, so as to minimize the ultimate

risk of property damage and loss of life.

This same hazard rating of 35 out of a possible 40 applies

generally to other areas lying along the fault line north

and south of the subject property. The hazard rating in

areas away from the San Andreas fault line would probably

range from a minimum of perhaps 22 to 25 in areas of sound,

massive rock to possibly a maximum of 38 to 40 in local

areas having severe landslide potential or gross danger of

vibration destruction (as the Devil Slide area along High

way I, o_r the reclaimed mud flats adjacent to the Bay).

Earthquake Design

Earthquake design can entail either minimum or maximum

damage hazard, depending on such variable factors as mate

rials (wood, masonry, or concrete), type of framework,

amount of reinforcement, and the size, shape, height, age,

and orientation of the particular structure.

152

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In existing developments, the earthquake damage hazard is

essentially fixed and unavoidable, whereas in new develop

ments, the hazard can be largely avoided, or greatly mini-

mized, by recognizing unfavorable conditions and either

avoiding them or creating counter design measures to

achieve acceptable risk.

Earthquake design measures in common use, as well as cur

rent building codes, are predicated on the assumption that

structures must be designed to withstand certain forces

of earthquake acceleration with respect to the static and

dynamic loads inherent in the particular structure. This

approach to earthquake design provides a general level of

protection from forces of shock and vibration, but rests

on the implicit assumption of foundation stability. That

is to say, I feel that current earthquake design., and

building codes, do not give adequate consideration to

local geologic conditions, soil characteristics, to vaga

ries of ground motion, or to the danger of foundation

failure. This inequity is best illustrated by noting '

that the same "universal" building codes apply to struc

tures located on reclaimed mud flats as on rock founda-

tions in the foothills. Reclaimed mud flats hold far

greater vibration damage hazard than sound, massive rock

153

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foundation in the surrounding foothills._.

I am not qualified to analyze the potential damage haz

ard inherent in the proposed "cluster-type" dwelling of

the proposed development, except to note that I feel they

should be designed to withstand strong ·thrust shock act

ing in directions parallel to the San Andreas fault. I

hold reservations as to the advisability of any multi-... story structures in the immediate area and feel that all

'. \ foundation and structure base members should be designed

with serious consideration of the possibility of ground

shifting and shear dislocation.

SU11B11ary and Conclusions

Earthquake hazard at the proposed site has been analyzed

with respect to earthquake frequency, geographic location,

local _geologic conditions, soil conditions, and struc

tural design. I conclude that the proposed site does in

deed straddle the main San Andreas fault line and that it

possesses inherent earthquake danger that approaches the

maximU111 hazard known to geologic science. As defined here

in, I feel that the site possesses a native hazard rating

of 35, of a possible maximum of 40, on the F.L.G.S. rating

154

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system. I feel that the earthquake history of the Bay

Area, our geological theory of cyclical origin of earth

quakes, the assumption that future earthquake activity

will resemble past activity, plus seismic records and

U.S. Coast and Geodetic survey measurements, all suggest

that it is just a matter of time until another major

earthquake strikes the Bay·Area. I think there is rea

sonable chance that the next major earthquake will orig

inate from movement on the San Andreas fault and that

it may well be accompanied by surface rupture, as in the

past.

To the question ... When will the next earthquake occur? ...

I can only reply that scientific discipline cannot yet

predict the occurrence of an earthquake in time or space.

It might come tommorrow, 100, or 1,000 years from now.

Notwithstanding, I feel that the survey of responsible,

professional opinion would show preponderant belief that

the Bay Area is due for another big earthquake in the

not too distant future. Indeed, there are many who main

tai.n that the Bay Area is overdue for a major shock.

For myself, I stress the reasonableness of the assumption

that future earthquake activity will resemble past activity

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and emphasize that future earthquakes comparable to that

in 1906 are inevitable, can occur at any time, and should

be anticipated in project planning and structure design.

I feel that progress is not accomplished by taking unnec-

essary risks.

I.recommend that the final project planning of structure

orientation, arrangement and design be certified by a

Structural Engineer with recognized eminent stature in

earthquake design.

Very truly yours,

FL~ct~~ng Geologist

FWA/do

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gmw.conservation.ca.gov · •• k. I Gribaldo, Jacobs, Jones and Asso.ciates Consulting Engineers • Soil, Foundation and Geological Engineers 333 Fairchil.d Drive (P.O. Box 669),