gmw.consrv.ca.govgmw.consrv.ca.gov/SHP/APSI_SiteInvestigationReports_OCR/APSI_0… · 18.06.1992 · I I I I I I I I I I I I I I I I I I I A.G.I. GEOTECHNICAL, INC. 7247 Hayvenhurst

I I I I I I I I I .. I I I I I I I I I

Response To L.A. County Review Sheet The Old Wrightwood Ranch Lots 1, 2 and 3 of Tract 45783 Los Angeles County, California

Project No. 2-1161-00 June 18, 1992

Prepared For:

Spindler Engineering 16823 Saticoy Street Van Nuys, CA 91406

Attn. Mr. Larry Gray

&@D - -- A.G.I. GEOTECHNICAL, INC.

I I I I I I I I I I I I I I I I I I I

A.G.I. GEOTECHNICAL, INC. 7247 Hayvenhurst Avenue, Unit A-2 - Van Nuy•, CA 11406 • (818) 785-5244 - FAX (818) 785-1251

316 Tejon Place, Palos Verdes Estates, CA 90274

June 18, 1992

Spindler Engineering 16823 Saticoy Street Van Nuys, CA 91406

Attention: Mr. Larry Gray

Project No. 2-1161-00

Subject: Response To L.A. County Review Sheet The Old Wrightwood Ranch Lots 1, 2 and 3 of Tract 45783 Los Angeles County, California

Dear Mr. Gray:

In accordance with your request, we have prepared this report in

order to update the project as the new Consultants of Record and to

respond to a County Review Sheet, dated 4/16/92. The scope of work

for this project included review of the referenced reports, maps

and publications (see list of references in the appendix),

discussions with you (the client) and with the County Geologist,

excavation of an approximately 123-foot long exploratory trench in

the vicinity of Lot 1 and the preparation of this report (including

maps and other graphics) which presents our findings and a response

to the County Review Sheet. A copy of the Review Sheet is included

in the appendix.

presented below.

For convenience, an itemized response is

Engineering Geology • Soil Engineering


June 18, 1992

1. L.A. County:

Project No. 2-1161-00 Page 2

The consultant geologist and geotechnical engineer must

designate a safe buildable area free of geotechnical hazards

on each lot.

A.G.!.:

In order to designate a safe buildable area, it was first

necessary to agree upon a "target area" for the investigation.

The reason for this is that the entire parcel is within the

Alquist Priolo Special Studies Zone for the San Andreas Fault

Zone. In lieu of an investigation of the entire parcel for

evidence of active faulting (i.e., continuously trenching the

length of the parcel), it was decided to limit the

investigation to an area of the parcel which is most likely to

be developed. The area chosen for the investigation (by Mr.

Larry Gray of Spindler Engineering) included an approximately

so-foot wide zone along the south side of the proposed access

road measured from approximately the midpoint of Lot 2.

In order to determine whether any active fault splays of the

San Andreas Fault cross this "target area," an approximately

123-foot long continuous trench was excavated on Lot 1 in a

direction approximately perpendicular to the mapped trend of

the San Andreas Fault. The trench was excavated with a

backhoe to a maximum depth of approximately 14 feet. The

trench extended from the level area in the vicinity of the

proposed access road (at the approximate midpoint of an east

trending gulley) south up the existing natural slope (see

Plate 1). The trench location was plotted by inspection in

the field using site topography as depicted on the referenced


June 18, 1992 Project No. 2-1161-00 Page 3

development plan by Spindler Engineering. No field stakes

were provided and no property corner markers could be located.

Geologic units encountered in the exploratory trench included

slopewash, residual soil, weathered and creep-affected

bedrock, and bedrock of the Pelona Schist Formation.

The slopewash encountered was generally three to six feet

thick and consisted of dark brown silty coarse sand with

bedrock fragments in a moist and moderately firm condition.

Note: The term slopewash is herein used to distinguish soil

which has apparently undergone transport and deposition from

soil which has apparently formed in place due to weathering of

the underlying bedrock. The term includes topsoil.

Beneath the slopewash was a zone of highly weathered and

creep-affected bedrock which ranged in thickness from four to

ten feet. It consisted of a variable mix of greenish gray to

gray residual soil (clayey silt to sandy silt), "residual core

fragments" of bedrock within residual soil and hard (but

creep-affected) bedrock. The variability in the thickness of

this zone was apparently due to the variable hardness of the

underlying bedrock. In areas dominated by hard and brittle

siliceous metamorphic rocks, bedrock with identifiable

structure and continuity extended nearly to the ground surface

whereas areas dominated by softer mica schists were overlain

by a thick zone of weathered material containing little or no

visible bedrock structure. In areas where foliation in the

bedrock was identifiable beneath the weathered zone, a change

in dip angle was generally discernable across the transition

from relatively unweathered bedrock to highly weathered (and

creep-affected) bedrock.



The bedrock underlying the site has been assigned to the

Pelona Schist Formation. Bedrock observed in the trenoh

generally consisted of dark gray mica schists and siliceous

metamorphic rocks which have been weathered differentially

according to composition. The bedrock was generally highly

fractured and moderately hard to locally very hard. Foliation

in the bedrock generally strikes in a northwest direction and

dips moderately to steeply to the south.

Although the bedrock was generally highly fractured, no

through-going gouge zones, disrupted soil contacts, springs,

seeps, etc. were observed in the trench.

The results of our field investigation indicate that

residential construction is feasible south of the proposed

access road within the setback limits shown on the

accompanying map. The setback limits are based on a 15'

setback from each end of trench T-lA and on a projected trend

of N65°W across the site, which is the general trend of the

san Andreas fault in the site area. The setback limits

presented shall supersede the setback limits contained in the

referenced reports.

The setback limits presented herein necessitate a

reinterpretation of subsurface conditions on Lot 3 from those

presented in the referenced reports. It is our opinion that

the southern of the two fault traces depicted in the previous

geotechnical maps does not cross Lot 3 between previous trench

T-2 and the east property line as shown. The control points

for this segment of the above inferred fault appear to be (1)

a contact between slopewash and alluvium (labeled "Probable

Fault Trace") encountered in Trench T-2 and (2) one of several


June 18 1 1992 Project No. 2-1161-00 Page 5

segmented photolineaments presented by Allen Seward during an

investigation for the parent tract. Apparently neither of

these control points for the inferred fault received the

benefit of verification by continuous trenching into bedrock

across their path. The continuous trench excavated by this

office (into bedrock) on Lot l is located across the projected

traces of both the photolineament by Allen Seward and across

the "Probable Fault Trace" reported in Trench T-2.

It should be recognized, however, that the setback limits

presented herein do not dispute the presence of the remaining

fault traces depicted on the previous geotechnical maps

(mainly north of the proposed access road). In addition,

because the site is entirely within the Alquist-Priolo Special

Studies Zone, we recommend that the remainder of the site

which has not been trenched in a continuous fashion be

designated as Restricted Use pending future investigation.

The Restricted Use designation applies to all habitable

structures but does not apply to sheds, detached garages,

roads, driveways or septic systems.

Note: All recommendations presented in the referenced

geotechnical reports concerning grading and/or construction of

the proposed improvements which are not amended herein remain

in effect and should be followed. All grading should be

observed by a representative of this off ice to see that the

work is performed in accordance with our recommendations and

to ensure that site conditions are as anticipated.

Any future development plans for the subject lots should be

reviewed by a representative of this office to ensure that all

pertinent design recommendations and required setbacks are



taken into account. If, at any time, it is desired to remove

the Restricted Use designation for any of the remaining

portions of the parcel, an additional detailed field

investigation would be required. Depending on where any

future proposed structures are located on Lot 1, it may become

necessary to excavate and recompact the loosely backfilled

trench excavated for this investigation.

rt should be recognized that the subject site is located in a

very seismically active area. The intent of this

investigation and report is to minimize the risk of primary

ground rupture beneath proposed habitable structures by

requiring them to be located away from known active fault

traces. Such required building setbacks will reduce the risk

of damage to structures during small to moderate earthquakes

by reducing the risk of primary differential fault movement

occurring beneath the structures. such building setbacks,

however, do not prevent damage during large earthquakes due to

ground shaking. (In addition, surface ruptures during

earthquakes do not always follow previous ground breaks and

may occur anywhere within a fault zone).

If a large-magnitude earthquake were to occur on the San

Andreas Fault in the Wrightwood area, many homes will

experience severe structural damage or even collapse,

including any future homes constructed on the subject lots.

No guarantee is herein expressed or implied that any portion

of the subject parcel will be free from primary ground

rupture, damaging ground shaking, debris flow or rock fall

during a major seismic event.

should be made known to any

renters, etc. It is understood

Full disclosure of this fact

future buyers, developers,

that the homeowner or renter



2.

assumes all responsibility for the risk associated with

residing in the Wrightwood area.

L.A. County: Provide a "change of consultants" letter from

the new geotechnical consultants stating that they are the

Consultants of Record and that they have reviewed the reports

by the previous consultants and agree with their findings,

conclusions, and recommendations or present their own.

A.G.I.

3.

We have prepared a Change-Of-Consultants letter for the

subject project, dated June 18, 1992. As mentioned above, we

have reviewed the previous geotechnical reports for the

project and generally agree with their findings and

recommendations. However, we herein modify the previous

recommendations concerning Restricted Use Areas. It may be

necessary to modify other recommendations as new development

plans become available or as conditions encountered during

grading may warrant. Additional field work and/or analyses

may be needed on a lot-by-lot basis as plans become available.

L.A. County:

Provide a letter from the consultants regarding Restricted Use

Areas (showing where they are and referencing reports).

A.G.I.

Because the Restricted Use Area boundaries serve as the limits

of the "safe buildable areas" referred to in item no. 1, the



reader is referred to the above discussion. Restricted Use

Areas are shown on Plate 1.

4. L.A. County:

Depict Restricted Use Areas on the Final Map.

A.G.!.

No response. Compliance is under the purview of the Civil

Engineer.

s. L.A. county:

Submit 3 copies of the Final Map that have been signed and

stamped on each sheet by the geotechnical consultants.

A.G.!.

We will review the Final Map when it becomes available.

6. L.A. county:

Provide a receipt for verification fees of $360.

A.G.!.

No response.



This opportunity to be of service is sincerely appreciated. If you

have any questions, please contact our office.

Respectfully submitted,

A.G.I. Geotechnical, Inc. - ----_-·::-.:>"" _.----1

// ........... / .. -··:>-;...-5----~----..,.-:_.,_/ -- ,/

{_ __,'{__,,,,_ -Eric Smith

Senior Geologist

1~0-! <-~f"-----Keith W. Ehlert, C.E.G. 1242

ES/KWE:el

Enclosures: List of References Figure 1: Location Map (including overlay of A.P.

Zone) Figure 2: Geologic/Seismic Hazard Map (Envicom,

1975) Plate 1: Site Geologic Map (including Restricted

Use Areas) Plate 2: Log of Trench T-lA Copy of Review Sheet, dated 4/16/92

Distribution: (6) Spindler Engineering Attn. Mr. Larry Gray


June 18, 1992 Project No. 2-1161-00

R E F B R B N C E S

Barrows, A.G., and others, 1985, Earthquake Hazards and Tectonic History of the San Andreas Fault Zone, Los Angeles County, California: California Division of Mines and Geology Open File Report No. 85-10.

Envicom Corporation, 1975, Investigation of the San Andreas Fault Zone, Expected Earthquake Shaking and Slope Instability, Wrightwood, San Bernardino County, California, dated July 1975.

Hart, Earl W., 1990, Fault-Rupture Hazard Zones in California, Alquist-Priolo Special studies Zones Act of 1972 with Index to Special Studies Zones Maps: California Division of Mines and Geology Special Publication No. 42.

Los Angeles County Department of Public Works, Materials Engineering Division, Geologic Review Sheet, dated April 16, 1992.

Ross, D.C., 1969, Map showing Recently Active Breaks along the San Andreas Fault between Tejon Pass and Cajon Pass, Southern California: U.S. Geological Survey Map I-553.

RSA Associates, Inc., 1988, Alquist-Priolo study and Soils Engineering and Engineering Geologic Report Update, Job No. 3775-oo, dated January 4, 1988.

RSA Associates, Inc., 1988, Results of Percolation Tests, Job No. 3775-01, dated July 13, 1988,

RSA Associates, Inc., 1990, Response to L.A. County Review Sheets, Job No. 3775-02, dated July 30, 1990.

RSA Associates, Inc., 1990, Response to L.A. County Review Sheets Dated 10/25/90, Job No. 3775-03, dated December 4, 1990.

RSA Associates, Inc., 1991, Response to L.A. County Review Sheets Dated 10/25/90, Job No. 3775-03, dated January 31, 1991.

RSA Associates, Inc., 1991, Response to L.A. County Review Letter Dated June 19, 1991, Job No. 3775-04, dated August 6, 1991.

RSA Associates, Inc., 1991, Response to County Geotechnical Engineering Review Letter Dated June 19, 1991 and County Geologic Review Letter Dated June 26, 1991, Job No. 3775-05, dated August 22, 1991.

RSA Associates, Inc., 1991, Debris Flow, [Analysis Of Potential for) Job No. 3775-05, dated September 18, 1991.


June 18, 1992 Project No. 2-1161-00

R E F E R E N C B S

Spindler Engineering, Grading Plan - Tract 45783, dated September 1, 1987.

State of California, Special Studies Zones, Mount San Antonio Quadrangle, Official Map-Effective July 1, 1974, Scale: 1"=2000 1 •

u.s. Geological Survey, Mount San Antonio, California, Quadrangle (1988), scale: 1 11-2000 1 •

.. ·~

' -

LOCATION MAP

Source: U.S.G.S. Mount San Antonio Quadrangle (1988) FIGURE 1 Project No. Date: 2-1161-00 6/18/92

~&@O~ A.G.I. GEOTECHNICAL, INC. Scale: 1 .. _ 2000 , Revised:

Drawn by: TW


LOCATION MAP

Source: U.S.G.S. Mount San Antonio Quadrangle (1988)


~&@D~ A.C.I. OEOTECHNICAL, INC. Scala: l" " 2000'

FIGURE 1 Date: 6/18/92

Revised:

Drawn by: TW

I I I I I I I I I I I I I I I I I I

Explanation:

------------

GEOLOGI({SEISMIC HAZARD MAP

Fault Hazard Zone. Includes 1857 Break (heavier dashed line) and other faults in the Zone of Major Faulting

\ \

Source: Envicom Corporation, Geologic/Seismic Hazards Map (Plate 1), Wrightwood, CA. June lg75 Fl GURE 2

- ill@D - ~-· A.G.I. GEOTECHNICAL, INC.


Scale: l" "' 400 ,

Approved by: _ ..... _ c:::....-1-...... .

' / ·/

Date: 6/l8/g2

Revised:

Drawn by: TW

I T01

FROM:MATERIALS ENG.D!U. ro: 818 785 5244 3· 12PM APR 22, 1992

Subd1v1slon S1ctlcn GEOLOGIC REVlrll

I FRI>!• Materials Eng1n .. r1ng Dlvhlon

SUBJECT! REVIEW OF FINAL MAP WITH PROCESSIHO

Dat11 4/18/92

I CENTER DATE __,3""'/2,,_4"'"/"'92._ ____ _

45783 I PARC Et OR TRACT MAP . tfO. :

LOCATION: 1'Wrlghtwood

HZn Unit of Traet: \

Job I L12 ! ~ Z § 1 //

I [!] Th1' m~p has not in~t th• requlramonts for filing for th• following reasons•

I I I

The consultant gtologlst and g1ottchnlcal •ngln11r must des1gnat1 1 'aft bu1ldab1t aria fr11 of gtot1chnlcal hazards on .. ch lot.

Provide a "chang1 of consultants" letter from th• newgeoteehnlca1 consultants stating that thly are thl Consultants of Record and that thay have reviewed the reports by the previous consultants and a9r11 with their findings, conclusions, and recommandatlon• or present their own.

Prcvlde a 11tt1r from the consultants re9ardlng Restricted Use Areas (show1ng whar1 they 1r1 and refar1nc1ng reports).

Depict Re1trlct1d Us1 AR11s on the Final Map.

Submit 3 cop11S of the Final M1p that have been sl;n•d and stamped on tlch sheet by tht ;tottchnlcal consultants.

Provide a receipt for verification f"s of $360.

1 Prepued by -~"'----"'---;,."', -~...-:-=---- Reviewed by ___________ _

I !Jr Oate 4/16/92

Charles N11tl1.

I G3:45783

I

P.02

-...... __ -....... ...........__

' . ' OVERSIZED~·~·

DOCUMENT HA.S BEEN PULLED AND SCANNED WITH THE MAP·.

FILE. .. .. _

... - ' ·-

' ,,,,

•

RSA Associates, Inc. Since 1956

C..:arporale C.>ffice: I S.414 (.abrito Road, Unit A, Van Nuy~, C:A q1406 • !818) 989·5338 • 26545-Bl Felix Valde.z: Avenue, Kanc:hoC:.'!lifornia. CA 92}9U• (714J 1)7b-8J82

A-v.Jutf Z I ( p~.- ?--"- It') ~ly;J.O..,. i990

The Old Wrightwood Ranch, Inc. c/o Spindler Engineering 7120 Hayvenhurst Avenue, Ste 200 Van Nuys, CA 71406

Job No.: Log No.:

3775-02 17407

Attention: Mr. Larry G. Gray Vice President

PROCESSING l,t11iiEH LAl~D DEV. DIV.

Subject: RESPONSE TO L.A. COUNTY REVIEW SHEETS DATED 6/19/90 AND 6/27/90 Lots l, 2 and 3, Tract 41777

Dear Mr. Gray:

The following are our responses to questions raised in the

L.A. County Geologic Review Sheets dated 6/27/90 and in the

Geotechnical Engineering Review Sheet dated 6/19/90.

GEOLOGIC REVIEW SHEET {6/27/90)

L.A. COUNTY:

l. Section 309 code requirement not met.

RSA:

We already provided a 309 statement on

preliminary . report of January 4, 1988.

located in a very high risk area. We

page 2 3 of our

This site is

feel that this

site as well as most of the community of Wrightwood has

Engineering Geology• Soil Engineering• Material Testing

1. ' ,,

The Old Wrightwood Ranch, Inc. -Juiy-.3..G-, 19 9 0

Job No.: 3775-02 Log No.: 17407 Page 2 hv;Jojf "J,/J

a safety factor less than 0.5 during a large earthquake

event on the San Andreas Fault, We reco:mmend compliance

with Section 308{c) where the applicant has submitted a

geological report complying with Section 309 which

report indicates that the site appears to be

geologically safe for the proposed use in the absence of

a major earthquake but is located in an area subject to

a hazard of a geological nature,

L.A. COUNTY:

2. Submit complete "geologic map" of Tract 45783 with

appropriate geologic cross sections. Indicate on cross

sections the depth of surficial materials and nature of

bedrock materials especially in the area of proposed

building sites.

RSA:

We have included is a copy of our original ,Geologic Map

and Cross Sections. A 15 foot setback has been shown on

the south side of the southern-most fault trace.

L.A. COUNTY:

3. Indicate on the geologic map the grading necessary in

order to create a building pad for each lot (1,2,3) and

any corrective work necessary (see attached Geotechnical

Engineering review sheet).

RSA Associates, Inc.

The Old Wrightwood Ranch, Inc. August 21, 1990

Job No.: 3775-02 Log No.: 17407 Page J

RSA:

No building plans have been submitted to us. The

current owner plans to provide only street improvements

at this time. However, the following recommendations

apply to any future proposed grading for building pads.

L.A. COUNTY:

4. Submit all necessary slope stability calculations (gross

and surficial) (static and seismic) for all natural and

envisioned graded slopes which may affect the proposed

building sites.

RSA:

calculations were made by simplified Bishop's method to

evaluate the minimum safety factor. Because .,no bedrock . ,.·,

sample was available a cohesion value o~ '500. psf and an.

angle of internal friction of JO degree is used as

representative cross bedding shear strength of the

bedrock. The cohesion value is assumed to be zero in

the case of shearing along bedding planes, Some

appropriate friction angles and cohesion value for

rocks and joint filling material reported by Hoek and

Bray are attached to this report to justify the use of

the above mentioned shear strength parameters. The

minimum static safety factor is 1.7 that is higher than

1.5 the minimum required by the Code.



Job No.: 3775-02 Log No.: 17407 Page 4

Pseudostatic analysis were made to evaluate the minimum

seismic safety factor of the slope. Although in these

calculations the lower limit of estimated repeatable

ground acceleration corresponding to an earthquake on

San Andreas Fault having a magnitude of 8.25 is used,

the calculated minimum safety factor is only about O. 5

and much below 1.1 required by the building code. We do

not recommend any mitigation measures because in our

opinion mitigation measures are not feasible. The owner

may contact the Land Development Department of Los

Angeles County to sign a hold harmless agreement.

No calculations were made to evaluate the stability of

slope surface, because topsoil and slopewash are

classified as loose in our geologic report. Mitigation

measures were recommended in our original report No.

3775-00 dated January, 1987.

GEOTECHNICAL ENGINEERING REVIEW SHEET (6/19/90)

L.A. COUNTY:

1. Provide additional consolidation test results to

determine the area and depth of collapsible soils.

RSA:

Because no building pad was anticipated to be located on

the flatter portion of the site, no consolidation tests

were performed on alluvium. If it is decided to



Job No.: 3775-02 Log No.: 17407 Page 5

construct at the end of the driveway in the flat portion

of the site, all topsoil, slopewash, alluvium and

weathered bedrock in the area of proposed development

and 25 feet beyond building lines in all directions

should be removed, and replaced as compacted fill to the

proposed finish grade in order to decrease the

probability of liquefaction and subsidence. All

excavations or soil removals and all building pads on

the slope or flat part should be examined by our

geologist for verification of the required established

15 foot setback from a fault trace and to inspect during

construction grading for the potential of ground

rupture.

L.A. COUNTY:

2. All soils subject to hydroconsolidation under the

structures and beyond the line of influence of the

RSA:

building foundation must be mitigated.

mitigation measures.

Comply. Please see above item.

L.A. COUNTY:

Recommend

3. Areas not recommended to be mitigated must be designated

as "Restricted Use Area" if the depth of collapsible

soils is more than 4 feet.



Job No.: 3775-02 Loq No.: 17407 Page 6

RSA:

Since depth of topsoil, slopewash and alluvium exceed 4

feet, the subject site should be considered as

restricted area unless on-site materials are processed

in accordance with our recommendations.

4. Provide the following for the proposed slough wall:

RSA:

a. Volume calculations to determine the total amount of slopewash material which could break loose. The slough wall must be designed to contain 100% of the volume and must consider splash-over effects.

b. Design parameters including impact forces.

c. Required wall height.

No building plans have been submitted to us. The

current plans show only a street improvement at this

time. However, if it is intended to locate a building

pad at the end of the driveway. Because this flat

portion of the site is located inside a natural drainage

channel, a civil engineer should design appropriate

diversion channels and determine the height of the

building pad in order to be at least 2 feet above the

anticipated highest flood elevation. All required

setbacks from this channel should be in accordance with

setback requirements of the agencies having

jurisdiction.



Job No.: 3775-02 LogNo.: 17407 Page 7

When the building plans become available to us we will

calculate the required height of slough walls in

accordance with the L.A. county requirements. All

slough walls should

least 150 lbs/cu. ft.

resist an impact pressure of at

of equivalent pressure and they

should be founded on firm sound bedrock or compacted

soils in accordance with our recommendations.

L.A. COUNTY:

5. Show the following on the geotechnical map:

RSA:

a. Existing and proposed grades.

b. Proposed building sites.

c. All grading and corrective work required for the building sites.

d. The area and overexcavation depth required for soils subject to hydroconsolidation and for slopewash and alluvial material.

e. Location of private sewage disposal system.

f. Restricted Use Area.

The grading plan is for a proposed street access only.

No proposed building sites have been designated at this

time.

a. To be provided by the project civil engineer.



Job No.: 3775-02 Log No.: 17407 Page s

b. To be provided by the project civil engineer or architect.

c. To be provided by the project civil engineer.

d. Appropriate recommendations are provided in our reports, we will show the limits on our plans when the building pad locations are available to us,

e. To be provided by the project civil engineer in accordance with the recommendations in our report No. 3775-00 and 3775-01.

f. All of the subject site should be considered as restricted use area unless the on-site materials are processed in accordance with our recommendations,

L.A. COUNTY:

6. Show the following on the grading plans:

a. The area and overexcavation depth required for soils subject to hydroconsolidation and for slopewash and alluvium material.

b. Location of private sewage disposal system.

c. Proposed slough wall.

d. Proposed building sites.

Again, the proposed building sites are unknown. However, our recommendations for the future location,

grading and foundation work for these structures should

be followed.


I ,


Job No.: 3775-02 Log No.; 17407 Page 9

RSA:

a. We will indicate the area on our plans when building plans become available to us, the depth of removal is the depth to the sound bedrock.

b. To be provided by the civil engineer in accordance with our recommendations.

c. We will show them on our plans when building plans become available to us.

d. To be provided by the civil engineer or architect.

L.A. COUNTY:

7. Provide data on the possible adverse impact of the

private sewage disposal system relative to site

stability and adjacent properties.

RSA:

The sewage disposal system should be designed in

accordance with our previous recommendations presented

in our reports No. 3775-00 and 3775-01. However, if a

building area is located on the flat portion of the

site, we recommend the sewage disposal to be at least

100 feet away from the building area in order not to

saturate the soil close to the building, to avoid

eventual liquefaction and/or loss of strength due to the

anticipated severe shaking.

L.A. COUNTY:

8. The Geotechnical Engineer must review the grading plans

and sign and stamp the plans in verification of his



Job No.: 3775-02 Log No.: 17407 Page 10

RSA:

recommendations and the recommendations of the approved

geotechnical report.

We will review the grading plans upon our clients

request.

L.A. COUNTY:

9. Requirements of the Geology Unit must be complied with.

see response to Geologic Review Sheet (6/27/90) above.

L.A. COUNTY:

10. Please include a copy of this review sheet with your

response.

RSA:

Comply.



Job No.: 3775-02 Log No.: 17407 Page 11

This opportunity to be of service is greatly appreciated. If you have any questions concerning this report, please do not

hesitate to contact this office.

Very truly yours,

RSA ASSOCIATES, INC.

~~~~U..-Michael Scullin, C.E.G. 170

i~.E. 861

MS/SM/JAV:el

Enclosures: Geologic Map Stability Section Calculations

Seyed Morteza Mortazavi, Ph.D. R.C.E. C 044091

Typical shear strength data

Distribution: (6) The Old Wrightwood Ranch, Inc.


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.llA!ls F'S• lCL+ IWCosQ _,.

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Sh'°' Siren lh Porom1lt•I

Col'I es ion • c ( lbs /sq. ft)

Angle of lnternol li'ictlon ·4' 3 Cl

Tongenl 4'

Slldt Cohulon Plo•t c Allglt

a (kafl

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'f(" C, + I 1 S-<'r- o. 4,,_/, ?~1rt.-1 "'

6 "f "''if ~"41..\'111Z.7

~" ;,'fS'" <I \ G 4C i


Job No. 3 '1 '1-r- .,.. 2 . Date 7- - ]o -1,q "'

Cohesion· C (lbs/sq. fl) 5 .-.,. o

Angle of Internal Friction ·ef> 3 <> .3 <"

Tangent ef>

111 p I A I.

-, Utiit Weight • Y (lb$/('ll. ft) l 2. 0

. I -

Toto I W•ioht Length

SHdt of L No. Slide (II.) w (kiPo)

I Zf) / oS

2 716' 55 3 !ff 1 D 3 6e>

ti 38'f~ I tr-5" 360D lfo

6 £'300 21° 'I 5 ~30 i 1~

~ l b'.30 'Jo

' \ ~ .,... 12 0

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0

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20 zo 21

11 3

-f i-2. 1.

=: 1- { t-+: 1 11 r r _ ~ 1~ b .·

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(ks!)

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' $

~

~

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I

"' ••

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Friel loft

4' 3o 54 ?. 5 lf \ 2 'l

f Zt·i" L/ Do 4tll

; 1f o 2- ~ 2..£.f G5tf

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FS:: Clt {WCosOi.np· KtWSinO ton'f! Z:WSlna • K lE WC010

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Job No. s'{'f)- 0 2 Section A - A/ Date t - lo - l'/ ~ u

• I_ - --2.._ ' .,.~

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Cohesion • C ( lbs /sq. fl)

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To1"9ent i/>

Utiit Weight • Y (lbs/cu ft I \ i ., l 2 "' Slldt .

Anglt Cohesion of

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a fkafl 4>

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/6 13~ 'i 0 c;- z_-go'f

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.

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f S l-1- tl'!.4-c·41.t44Z3

lf '-f 2-J -tO·l/ftll3!:'f-


.. ... , , ·--·" -TA --

Table 4.3 Some Approximate Friction Angles and Cohesion Values for Rocks and Join1 Infilling Materials

Rock

Andcsitc Basalt Chalk Diorite Granite Grcywacke Limestone Monzonite Porphyry Quartzite Sandstone Schist Shale Siltstone Slate

•• (intact rock)

45 48-SO

53-SS ·S0-64.

f

45-SO 30-60 48-65

64 45-SO 26-70 45-64 -so 4S-60

Infilling material

Rcmolded clay gouge C~lcitic shear zone material Shale fault material Hard rock Breccia Compacted hard rocic aggregate Hard rock fill

••(discontinuity)

31-35 47 3S-4J

40 44 27-38

37 43

From Hoek and Bray 1974; U.S. Department of Transportalion. 1977.

q,• (ultimate)

28-30

31-33

33-37 28-32 30-34 26-34 25-34

27-32

25-34

c (massive rock) kNm-2

100-300

50-150

100-300

50-l50

25-100 . -

•• (approximate)

10-20 20-27 14-22 22-30 40 38

' '

' '

' : I

I ,

OVERSIZED ~~

DOCUMENT HA.S BEEN PULLED.

A.ND SCANNED WITH THE MA.P

FILE. ·--

. ' '

•

Since 1956 RSA Associates, Inc.

Corporate Office; 15414 Cabrito Ro,ld, Uni I A. Vdn Nuys. CA g140b • (B 18) 989-5338 • 2854.5-82 Fi!lix V.i.ldez Av~nue, REln(hO C.l:liforn'ia. CA 92J9U· (:' 14) 67&-8382

January 31, 1991

The Old Wrightwood Ranch, Inc. c/o Spindler Engineering 7120 Hayvenhurst Avenue, Ste. 200 Van Nuys, CA 71406

Attention: Mr. Larry G. Gray Vice President

Job No.: Log No.:

Subject: RESPONSE TO L.A. COUNTY REVIEW SHEETS Dated 10/25/90 Lots 1, 2 and 3, Tract 45783 (Fonnerly a part of Tract 41777) Wrightwood Area Los Angeles County, California

Dear Mr. Gray:

3775-03 17811

.. ,,.., ..,..,,


Los Angeles county Geologic Review Sheet and in the

Geotechnical Engineering Review Sheet, both dated 10/25/90,

GEOI.OGIC REVIEW SHEET (10/25/90

1. L.A. COUNTY:

The fault trace flattens northward as it nears the

ground surface (T-1 and T-2). During a future rupture


• The Old Wrightwood Ranch, Inc. January 31, 1991

Job No.: 3775-03 Log No.: 17811 Page 2

RSA:

along this fault the trace could flatten to the south.

Should this occur, would the recommended 15' setback be

sufficient to preclude the chance of a fault rupture

occurring beneath a structure?

The contacts between Qsw and Qal, shown in the logs for

Trenches T-1 and T-2, were not meant to depict a fault

trace. The inference depicted is that the sub-vertical

portion of the contact represents a fault scarp that was

fairly rapidly buttressed by slopewash before

significant scarp degradation took place. Once the

scarp was buttressed, normal slopewash deposition

continued across this contact in a northerly direction.

The geometry of the inferred fault scarp suggests a

sub-vertical fault. We do not anticipate significant

flattening of the fault trace either to the north or to

the south should a future seismic event occur on this

inferred fault. We believe a 15' setback will be

adequate to protect proposed structures from possible

fault rupture should an earthquake occur on this fault.

We have, however, reevaluated the recommended setback

with respect to the northwest corner of the subject

parcel. Based on the findings of Envicom Corporation

(1975), Mr. Alan E. Seward (1981) and RSA Associates

(1988) it is clear that the topographic bench at the

north end of the parcel is underlain by one or more

subsidiary faults of the San Andreas Fault Zone. Most

of this topographic bench (and its associated anomalous


.. The Old Wrightwood Ranch, Inc. January 31, 1991

Job No.: 3775-03 Log No.: 17811 Page 3

east-trending swale) is included in the setback

(restricted use area) which we established previously.

There is, however, a triangular-shaped area,

encompassing portions of lots 1 and 2, which lies

outside the current setback line but which is part of

the topographic bench. There is reasonable probability

that this section may also be underlain by subsidiary

faults of the San Andreas Fault Zone. Therefore, we

have extended our original setback line to follow a more

linear course along the southern edge of this

topographic anomaly

recommend that no

(see revised Geologic Map). We

structures for human occupancy be

constructed north of this setback line. The area north

of the setback line, however, may be used for private

sewage disposal systems.

2. L.A. COUNTY:

RSA:

The consultants must depict the following on the

geologic map (for each lot): a) a safe building site;

b) any grading required to create this safe building

site; c) recommended sewage disposal area.

Provided all of our recommendations are followed during

grading and construction, all areas south of the setback

line may be considered safe (for the intended use, as

determined by traditional methods of analysis) from

hazards associated with normal hillside processes, as

well as from the hazard of ground rupture due to


•

•

The Old Wrightwood Ranch, Inc. January 31, 1991

Job No.: 3775-03 Log No.: 17811 Page 4

faulting.

Appendix A.

See Seismic Stability calculations in the

It must be noted that the current engineering practice

is based on the existing ground motion records to date.

No records have yet been obtained of strong ground

motions in the immediate vicinity of a fault. The

nearest strong motion record to fault rupture was 80 ID

in the 1966 Parkfield earthquake, with a 5, 5 Richter

magnitude. Larger measured magnitudes have been

recorded at a substantially greater distances. Hence,

the current engineering practice for immediately

adjacent to strong ground fault rupture has been

extrapolated, and has never been verified to date by

engineering measurements.

Therefore, although analysis indicates that "safe"

building sites exist at the subject site, one must

realize that there exists a risk that the intensity of

projected ground shaking, ground lurching, or

seismically-induced earth flows as a result of a major

earthquake occur on the San Andreas Fault in the

vicinity of wrightwood may exceed that projected herein

and result in damage and/or slope failures. For this reason we recommend that the owner, and future buyers be

provided with copies of our reports and made aware of

these hazards .

At present, the tentative map proposes street grading

only. It is our understanding that the lots are to be

recorded and sold ungraded. This, of course, is common

practice. All potential purchasers, however, should be



Job No.: 3775-03 Log No.: 17811 Page 5

informed in writing of the potential hazards associated

with the subject parcel which are described above and in

our previous reports.

a. Comply. We have shown recommended building sites

for each lot. As stated above, these sites are

safe from the hazard of ground rupture and from

hazards associated with normal hillside processes

provided all of our recommendations are followed

during construction.

b. The tentative map proposes street grading only.

The grading plan serves as the base for our

Geologic Map. It is our understanding that the

three lots included in the subject parcel will

likely be developed separately.

c. The recommended sewage disposal area is shown on

the plot plan accompanying our report of

percolation testing, dated July 13, 1988. The

reader is referred to that report. Restricted use

areas may be used for private sewage disposal

systems.

3. L.A. COUNTY:

Verify date of report (Job No. 3775-02): a. 7/30/90

(pp. 1 and 2, calculations and 2 plates) or; 8/21/90

(pp. 3-11).



Job No.: 3775-03 Log No.: 17811 Page 6

RSA:

This clerical error has been corrected.

date of the report is 8/21/90.

The correct

4, L.A. COUNTY:

Comply with Geotechnical Engineering Unit's review sheet

... dated 10/25/90, attached.

RSA:

See response to Geotechnical Engineering Review Sheet,

dated 10/25/90, below.

5. L.A. COUNTY:

Reports should address Tract 45783, not 41777.

RSA:

This oversight has been corrected.

GEOTECHHICAL ENGINEERING REVIEW SHEET (10/25/90)

L L.A. COUNTY:

The report indicates that the seismic slope stability

analysis is below safety factor 1.1. Recommend

mitigation measures, a hold harmless agreement is not

acceptable.



Job No.: 3775-03 Log No.: 17811 Page 7

RSA:

We have reviewed and re-computed our analysis. The

results are presented in the Appendix. In accordance

with current accepted Los Angeles County geotechnical

engineering practice, the pseudo-static analysis

indicates that a minimum factor of safety of 1. L+~ts

at the site. It is our opinion that all residential

- ---- structures in Wrightwood will be subjected to very high

9)l'tl'1Dd motion due to earthquake activity on the San Andreas Fault. The site, if built with impact walls and

diverter walls, appears to be geologically safe for the

proposed use but is located in an area (Wrightwood)

where the hazards, as analyzed herein, may be exceeded

in the event of severe activity along the San Andreas

Fault.

Potential Hazards

The method of

required by

pseudo-static analysis of slopes as

Los Angeles County evaluates seismic

stability of deep seated potential failure. We are not

aware of known seismically induced deep seated

landsliding in hard rock formations such as at the subject site. The well known cases of massive

seismically induced ground failure were a result of

severe loss of strength of sensitive clays or from pore

pressure buildup in fine sandy materials brought about

by the intensity of shaking. The site bedrock is not

subject to severe loss of strength. It is our opinion,

given the favorable results of pseudo-static analysis



Job No.: 3775-03 Log No.; 17811 Page a

that the possibility of seismically induced bedrock

failure is very low.

On the other hand, buildup of pore pressure due to

shaking in the surficial soils resulting in flows merits

consideration. It is our opinion that the potential of

seismically induced debris flows at the subject site are

probably not greater than the potential under severe

rain or snow melt. We base this on our shear test

results, which indicate firm materials, slopes are less

than 2:1 in steepness, and the that previous

investigation on the subject site by Allen E. Seward

Engineering Geology Inc. and Brian Robinson and

Associates, Inc. found sufficient jointing and

permeability in the Pelona Schist to suggest that a

phreatic surface may not be able

bedrock contact. Without a

liquifaction can not occur.

2. L.A. COUNTY:

to form along the

phreatic surface

As previously requested, provided the following

information for the proposed slough wall:

a. Volume of debris anticipated to break loose.

b. Wall height and/or required catchment area.

Show the proposed slough wall on the geotechnical

cross-section.



Job No.: 3775-03 Log No.: 17811 Page 9

RSA:

a. We have calcula.ted the watershed which is tributary

to the proposed development area to be

approximately 2.32 acres. Using guidelines

outlined in·the city of Los Angeles• Memorandum of

General Distribution #63, we have assumed a value

of 400 cubic

debris which

event. Thus

yards per acre for the volume of

could break loose during a single

the volume of debris anticipated to

break loose is 928 cubic yards,

b. All slough walls should be a minimum 5 feet high

and

of

should be designed to resist

at least 150 lbs/sq.ft,,

an impact pressure

equivalent fluid

pressure. No catchment area is required. It is

pro_p(>~l:l<'! __ t.o~ -dly~""i_J;:·:th"e_ii;;-;.- t·~-th-;-;ri:;;te proposed ---- '' 1-··-· .. ··-·· .......... """"'"""" '"-··-·-· --··· ·-·,,···· •'"" "'"' __ ..,_

street. _The low ridge north of the proposed road

-·-wTrr·a~t- in combination with the slough walls to

prevent any mud flow which is generated on-site

from affecting down-slope properties.

Recommended slough walls are shown on the attached

Area Map and on the revised cross section A-A'.

3. L.A. COUNTY:

Comply with item No. 5 of the Geotechnical Engineering

Review Sheet dated 6/19/90.

Item 5 of Review Sheet 6/19/90 states:


•

•


Job No.: 3775-03 Log No.: 17811 Page 10

RSA:

Show the following on the geotechnical map:

a. Existing and proposed grades

b. Proposed building sites ·

c. All grading and corrective work required for the

building sites

d. The area and overexcavation depth required for

soils subject to hydroconsolidation and for

slopewash and alluvial material

e. Location of private sewage disposal system

f. Restricted Use Area

The tentative map proposes only street grading at this

time. It is our understanding that the lots included in

this parcel are to be t-ecorded and sold ungraded.. It is

common practice to do so provided full disclosure is

made in writing to prospective buyers concerning any

potential geologic hazards associated with the property.

We have shown recommended building sites on the revised

Geologic Map. We have established restricted use areas

and shown them on the revised Geologic Map. We have

sbown recommended areas for private sewage disposal (See

RSA report, dated July 13, 1988). It would, however, be

fruitless for us to speculate on the configuration of

the proposed future building sites. We have made

recommendations for all grading and corrective work

necessary for the building sites. These recommendations

should be followed by any design civil engineer who

prepares a grading plan for any of these lots. We will



Job No.: 3775-03 Log No.: 17811 Page 11

be happy to review any such grading plan with respect to

our recommendations when such becomes available.

4, L.A. COUNTY:

RSA:

Th~ Geotechnical Engineer must review the grading plans

and sign and stamp the plans in verification of his

recommendations and the recommendations for the approved

geotechnical report.

plans for review.

Submit a complete set of signed

We will review the grading plans upon our client's

request.

S. L.A. COUNTY:

RSA:

The Geotechnical Engineer must sign, stamp and indicate

the date of registration expiration on the soils report

and all addenda.

No comment.

6. L.A. COUNTY:

Requirements of the Geology Unit must be complied with.



RSA:

Job No.: 3775-03 Log No.: 17811 Page 12

See response to Geologic Review Sheet, dated 10/25/90,

above.

7. L.A. COUNTY:

Please include a copy of this review sheet with your

response.

RSA:

Comply.

This opportunity to be of service is greatly appreciated. If

you have any questions concerning this report, please do not

hesitate to contact this office.

Very truly yours,

RSA ASS CIA INC.

c is, Dietz R.G~ Expires: 3/31/92

~~ Michael Scullin, C.E.G.

CD/MS/JAV: el

170 ~·

Enclosures: Location Map, Geologic Map Geologic Cross Section, Area Map Copy of Geologic Review Sheet, dated 10/25/90 Copy of Geotechnical Engineering Review Sheet, dated 10/25/90

Distribution: (6) Mr. Larry G. Gray


LOCATION MAP

Antonio USGS Mount San l ( 1988) Quadrang e


Appendix A The Old Wrightwood Ranch, Inc January 31, 1991

Job No.: 3775-03 Log No.: 17811 Page: A. l

STRENGTH PARAMETERS FOR STABILITY ANALYSIS

General:

We obtained adopted "peak" and "ultimate" bedrock shear

strength parameters as discussed herein. The subject site

and ascending hillside is underlain with the Pelona Schist.

The Pelona Schist is foliated. Foliation dips favorably into

slope. The purpose of this discussion is to determine the

strength across foliation. Except for the weathered zone

immediately below the contact with slopewash, the schist is

too hard to sample with standard sampling equipment and test

in the standard soils test direct shear machine. We returned

to the site and obtained hard chunk samples of the Pelona

Schist from the remaining spill from our old trench

excavations taking the hard chunks as having come from the

bottom of trenches in the more competent bedrock.

Where the strength of rock in a formation are relatively

high, the over all strength of the formation will be

controlled primarily by discontinuities such as bedding

planes, joints and fractures (slippage along

discontinuities), and secondarily by the strength (or

rupture) of the intact rock material. For the case at hand,

the significant discontinuities consist of joints and

fractures.. Foliation is favorably oriented for gross

stability. The rock formation mass quality and strength of

intact rock in formation must be determined.



strength of Intact Rock

Job No.: 3775-03 Log No.: 17811 Page: A.2

In order to quantify the strength parameters

rock material, the unconfined compressive

determined. The Chunk samples obtained from

of the intact

strength was

the site were

sent to Smith Emery's laboratory to be cored and cut with

their rock cutting equipment into a test prisms. The samples

were returned to our laboratory and submerged under water

for one week. Only one out of four samples was cored so that

its axis was perpendicular to the foliation, however, all

sa~ples were tested. The samples were placed in a concrete

compression test machine and loaded to rupture, Failure

occurred abruptly with diagonal cracks and/or vertical splits

forming. As expected for anisotropic materials, samples that

failed along foliation plane tested weaker, than the sample

that failed across foliation.

Table 1 below.

The results are presented in

The results of Sample No. 3, the sample which failed across

foliation, were taken as the cross bedding unconfined

compressive strength. A value of 1000 ksf (6944psi) was

adopted for subsequent calculations.

\.


• Appendix A Job No.: 3775-03

Log No.: 17811 Page: A.3

The Old Wrightwood Ranch, Inc January 31, 1991

Table 1

Compressive strength

Sample Least Rupture No. Height Dim lid Factor FQ;rce Area i:?:tress

1

2

3

4

Sample No,

l

2

3

4.25 11 1.75 11 2.43

4.51 11 1.75 11 2.58

3.20" 1.75 11 1.83

2.75 11 1.75 11 1.57

Comments

1. 00

1. 00

0.98

0.96

No visible joints. along foliation.

No visible joints. along foliation.

No visible joints, failed along plane foliation.

4200# 2.41112 1746psi

5200# 2.41112 2162psi

19250# 2.41 112 7830psi

3700# 2.41 11 2 1538psi

Foliation 75 •, Sample failed

Foliation 30', Sample failed

Foliation horizontal. 65' from horizontal

Sample across

4 Vertical joints. No foliation within sample. Sample failed along vertical splits and along plane 65' from the horizontal. Ruptured sample appeared to be more weathered than other samples.

Mass Quality of Bedrock Formation

The rock mass quality of the formation must be determined.

The method of engineering classification of jointed rock mass

of the CSIR (Commonwealth Scientific and Industrial Research

Organization) after Bieniawski was utilized and a tabulation


, Appendix A The Old Wrightwood Ranch, Inc January 31, 1991

Job No.: 3775-03 Log No.: 17811 Page: A. 4

for classification is presented in Plate Al. Six

classification parameters are required:

1. strength of intact rock

2. Drill core quality RQD

3. Joint spacing

4. Joint condition

5. Groundwater

6. orientation of joints

The first item was determined by laboratory testing. The

last four items were determined by observation and judgement

of our geologist. The RQD was approximated by an empirical

relationship based a spacing of joint sets

Engineering, by J. A. Frankl in and M. B.

presented in EQ.Q.t

Dusseault, 1989,

pp 51-2. Three near orthagonal joint sets were observed in a

road cut at the end of Timberline Drive with an average

spacing of 8 11 •

Volumetric Joint Count, Jv = 1/.2 + 1/.2 + 1/.2 = 15 / m2

RQD = 115 - 3.3Jv RQD = 65.5

The engineering classification of jointed rock mass for the

Pelona Schist formation of the hillside in question is

presented in Table 2 below. We computed a CSIR rating of 51

but conservatively adopted 44 for fair quality rock mass in

subsequent calculations.




1.

2.

3.

Table 2

Engineering Classification of Jointed Rock Mass

Strength: (50-100 MPa) = (7500-15000 psi)

RQO: assume 50-75%

Joint Spacing: 8" o. 3-lm

Rating

7

13

20

4. Joint Condition: slightly rough, soft wall < 1 mm 12

6.

4.

Ground water: moderate pressure (conservative)

Orientation: Slope / Favorable

4

-5

51 Overall CSIR Rating =

"Peak" Shear Strength

The peak strength was determined by a simplified empirical

failure criterion developed by Hoek and Brown, presented in

Rock Slope Engineering, by E. Hoek and J. w. Bray, the

revised third edition. The method utilizes the unconfined

compression of clear rock and the CSIR rating of rock mass

quality. The formula and applicable constants are

reproduced in Plate A2 herein. The parameters of this

formula are the unconfined compressive strength of the clear

rock, three empirical constants depending upon the

engineering classification of jointed rock mass, and the type

or origin of rocJc. The category for lithif ied argillaceous

rock was selected for schist. The constants A, B, and T were

taken for a conservatively adopted CSIR rating of 44,



nominally a fair quality rock mass.


For a

strength of 1000 ksf and the constants A = .234,

= -.0005 the following equation results:

compressive

B = .675 1 T

r = .234x(lOOO ksf) (o / (1000 ksf) - (-.0005)) .675

A plot of this formula is presented in Plate A3. A straight ·---~

\ line fit of a "cohesion" intercept of 3000 psf and phi = 35 • ) f-~,,,. L

./ 0

can be made. The above meth~ of determining peak stren_g:tlr/ ~/, = "">::-has been used in mining ~-;.;gii'iEHn--inq-----and----may ___ not-- be

appropriate for long term strength. However, it would be

quite appropriate as a seismic strength parameter for pseudo-

static analysis.

"Ultimate" Shear Strength

If the rock is sheared beyond the peak strength; shearing

will proceed along the cracks and ruptures that formed as the

peak was reached. As the cracks will probably not be

perfectly planar, the shear strength along these

discontinuities would consist of a basic phi angle

corresponding to the type of rock and the angle of the

asperities or the roughness of the joint or rupture surface.

The strength drops past the peak as slippage continues. The

ultimate strength of the rock is reached as the steeper

asperities along the joint/rupture surface are rode over or

sheared off. As slippage continues, more extensive damage

occurs to the joint surface and the remaining asperities are

eventual worn where only the residual strength of the base

rock remains along the slip surface.


I\~~. ·"'r';....., I.._~ -·- .-··' (J< .. i,_. '

i' ·--'



The following relations are based on N. Barton's method as

extended in the article "Strength, Deformation and

Conductivity Coupling Of Rock Joints", by N. Barton, S.

Bandis, K Bakhtar, Int. J, Rock Mech. Min. Sci. & Geomech.

Abstr. Vol. 22 No. 3 pp. 121-140, 1985. Originally Barton's

method was an empirical relation of the peak strength along

an existing joint surface. The required parameters are:

1. JRC Joint Roughness Coefficient which may

determined visually or by testing.

2, JCS - Joint Wall Compressive Strength - may be

determined by Schmidt hammer rebound tests.

3. ¢r - Residual friction angle.

The formula is

T ~ o tan (¢r + JRC log10 (JCS/a))

The parameters should be determined by testing, however, for

the case at hand, we selected a JRC = 20, JCS = 80 ksf,

¢r .. 28' by fitting the parameters to approximate the peak

relation 99mputed--by:.-, .. HQek and Brown's method above. A

residual .phi angle of 30' ··-;,<Jld probably be reasonable. The

.joint roughness coeff~c,j.,ent·· appears reasonable for rock just

ruptured. ±he ·· J~int strength coefficient fitted is

considerable less than that tested for intact rock. However,

surface weakening due to rupturing is to be expected. A plot

of the curve is presented in Plate A3.




The above cited article presents a standard method for

determining the shape of load deformation curve of rock based

a extensive research data. As the rock is strained past the

peak strength, Barton 1 s original relations is maintained,

except that the JRC is replaced with a JRC(mobilized) which

diminishes to zero as the residual strength is reached. The

ultimate strength is that computed substituting

JRC(ultimate) = 0.5 x JRC(peak) into the above relation. The

ultimate strength is plotted also in. l'l.ate A:t,._ A straight · ···

line fit of a "cohesion" intercept;.'6f 1000 psf a-~. phi = 32 • ) O I+, can be made. \...._ ·-~· ·1"" ':'· Z

0

To determine the load-deformation relation, deformation at

various stress levels must be determined. The peak

deformation, 6(peak) is given as

where

Ln JRCN' 33 6(peak) ~ 500 x Ln.33

= Joint length in spacing of cross at 18" = .45 m at

situ joints depth.

taken as average in meters, estimated

JRC adjusted to length of in situ joint. The same as determined above for the case at hand.

6(peak) = 0.0031 m = 0.12 11

The ultimate deflection 6 (ultimate) = lo x 6 (peak) . The

residual strength is reached at 6(residual) = 100 x 6(peak).

6(ultimate) = 1.2"

6(residual) - 12"

These values are required in deformation analyses.




SEISMIC STABILITY ANALYSIS

Since no continuous geologic structural weaknesses were

found that

calculations

daylighted or paralleled the slope, the

were made assuming homogenous strength

conditions and a circular type potential failure surface.

Calculations were performed on an IBM PC computer utilizing

the program STABL5/PC. Section A-A' was modeled for

analysis of the gross hillside stability. The gross

stability calculations were repeated to search for the most

critical computed surface under static conditions.

The search routine of the program was utilized, which

generates trial surfaces according to the search limitations

imposed. Points for initiation of trial circles were

selected in the area around to base of slope of the whole

hill side below the existing bench area through which the

fault traces pass, and the area of the toe of ascending slope

above bench. Four initiation points for generation of 40

trial surf aces from each point were specified around the

lower toe and five initiation points for generation of 40

trial surf aces from each point were specified around the

upper toe. The termination limits only the randomly

generated trial surfaces whose terminating point fall between

these two horizontal coordinates are accepted by the program

for analysis - were specified from just below the minor

break in slope to the last profile coordinates defined. The

ultimate shear strength parameters from our previous reports

were utilized(~= 30', c = 500 psf). The initial search did

not indicate an initiation point of sharply reduced factors

of safety, except that the lowest computed factor of safety

was obtained initiating at the toe in each search. For a




plot of the results see the attached computer print out in

Plates A4 and A5.

Two detailed searches were then performed, with each of the

above described toes defined as the initiation point for the

generation of 100 surfaces. The lower termination limit was

left unchanged.

to the lower

The upper termination limit was moved closer

limit. The most critical computed static

factor of safety was 1.990 from the lower toe and 1.869 from

the upper toe. For a plot of the results see the attached

computer print presented in Plates A6 and A7.

The most critical surface from the detailed search from each

toe was modeled and run with the peak shear strength

parameters (If' "' 35' C "' 3000 psf), and a pseudostatic

horizontal out of slope acceleration of .5g, and a vertical

upward acceleration of .25g to analyze seismic loading. The

computer factor of safeties of 1.100 for the lower toe and

1. 367 for the upper toe were

commonly accepted value of 1. 1.

presented in Plate AS.

obtained, greater than the

The computer print out is


]

J J J J J J J

__ J ]

J J J J J J J J

TAnllU. THI GEOMEmANJCS (:l.ASSll'ICAnON SYSTEM ro• JOllnm ROCll MASSES'

A. ~TIOH Pilla.AMITIU ANDntltHI lATINCf

.. 1"911.ftof hlni..laiMI'._,. >I ... ... I ••• U1111 .t •11illql ~PHl!Mwti ...---· ....._MP, "9r•md

in•lmrilll

• Uniii.:d1111IQ111111:~ -MP,

>100 t•·• ..... :i ... it~• :a.11 ••• - " " , - • ' • I

Drill .. qt111111titr ~ ... ,_ ,, __ ... _

:5-51'1> <"" I ..... .. " .. I I >

8C*lnf .. lcillt• »• 1~:11• ll·tlllt w-••• <ti-

' ...... .. .. .. ... I

v~" "1!.ll"' 111trf1C11. '~~MitfKm. Sl~fy ~ .wlMiB. S1id.ftl.lid..t ..,...,~ s.n:::o• Niii! coailnooua. N11 ~-.(:·-.. ~~<JIML i" .... tepmr111~. H.11d Hlild ~ ..,.11 taci.. Sol\lolnt-.Hfl!ld:_ ~< '111."'lt\fcl ..

CIJndttkin ol .... '""' wall tvt;l. .. juhmi-111inlll CrPt'l 1-1 m•. ! >l•a. • Contin\IOui: ioin411 ConU•llMQI

lolnG

·~ ... " .. " ' I • • I

lnllow plllt 10 iii N- <:-1$ -.,.,.ill I ~' 11'1 likn/miift -;.UI lllW"'illl ' h.Jn...i ~- I .. .. .. ..

Croundw•ler ..... ! I

lotntw.lw~ I ., ........ 2 '

>I.I

' ~pri~p11J .....

l :.1nvM.t ' .. .. .. G~""I COl'ldUIMI Cam"""tr cl:ry

~ IMlly lilll91"111101I NWMWllllllf~ ....... I rnodllftl~~ ·- " ' I • • I

Sutt1 udl~ -W11r.dMI .r . ..,..__ ·- ,. u.- .... -,.,., .... I _, -· -ti

_,,

"''• ,......._ • _, _, _,, _,, ·- • _, _,. i _,. -·

C. AIXK MAM~ ~ '11£111: IATINCt -- ' I • .. .. • - V•r'J 11101J rock """'- ··- --- V*l'J fl!*" l"llld!

Rallftf IOCl-to ,._,. ,,_,. I ,._,. <"

D Mf.ANINC OF mOCJI; .. ,,.. aAWl:I

o.1.- ' • .. .. y

... \•Hap !lilnd•up llmti ID f .. 'I lo!' ~fn 11t1mA fi--ihil 5111' ~ ... llPM 1-.•Swz-m.,,.. I ~hi-rot, ..... ~ ...• ,., ....... .,. Cohnlan n( lhli n11;• lllllllt. th , ... .,. __ ... ' lailTtll .,.. fridkin •na'-' .t th. ~Ii: IMll .... ...... ,. .... I »·•· .... I

C.v•bUMY'lll.,. V•ry poor W1111111 CIM '*9dlt,. •• I Will~mcf.U,. ........ ... "',...-, ! CO!ldf~WiMI. ·tr--i."'tlJll"Q.M_....,.. .... ..,........"'._~~illlt~U..-......._..~IMllil •I~ .. ..,..,r,tttui. • 191 ...... •Ul't/W. i"'~dll.amn.. .. .-...*'~

from Hunt, 1984 P/ak A I

t • 0

• • • • 0 .. • ~ • .. ~ • 0

0 g & 0 ~

• • .. • • .. ' • • g ~

0 • • • .. 5 • •

• 0 0 • • • g

• 0

~ g

• • ~ ~

~ • ... 5 • • •

- .

source: ~ Slope Engineering, E. Hoek & J.W, Revised Third Edition, page 108.

Bray,

- -APPROX I HATE RELATio"SHIP l!HllEEM ~OC( l<A$S "Q.uALtl'r AHO EllP1"1C~ CONSTANTS

__. • • "' N __. ll

__. ... .. "' .. ' 1 « 11 :!!;:! .... u 11 >o< "' .. j!: ~ ,., ... :i! .. g ·~ w- i: !I! 1: EllJ'il'ical faii"1"<1 cl'itel'itm " ... • .a • " ... .11 1-U j ... JN _ .... .. _ _, ... ... l ~.ii i ;J :;! '"lfu ~ ~ i! .a ;:t ...... "

'Iii 0'3 + lfli0ca3 • 1Ge2 ....

~I ~tnS .... "' ll f~3 li"~ 01 l2:;; j .... " <:> ,. .... u ...... .... .. "' "' g~ ~ i~9 1 ....

~1 ; gt; ·~ 'll

- ""~(•I a T_ )1 "'.., - .. - .... '""' _,.,_

11· t · .1' .. - ~~Ci """ :! "'" .,. ll < ..... _j- . . e . ·11- J -<:> "'" ..... 11111

i~ r O~OMJ :! :;: 11 .. .,_

:& .; l ~~ i:: -i~>~ u where T • i(m - /m2 ~ ~.) ].! "'"' ·~!

... u-<> .... -\2 "' .... ,,. 1

_.,, "' - " ll1 ...... eg w~~~ ... " 1- "' ...... l!'i:;~ .a 1 11~ "'u u ~ ...... .=! .... 0 _, --<:> u .... .... .. .... ., "--'"' u :! i

INTACT ROCK SAHPLES m • 7.0 .. - 10.0 .. . 15.0 ... 17.0 m • 25.0

Laborato111 li1f.s sps.cf.nums • - 1.0 ... 1.0 •• 1.0 5 • 1.0 • - 1.0 IN• f>'om joint• A• 0.816 A• 0.918 A• 1.044 A• 1.086 A• 1.220

CSilil r-;;1ting 100 B • 0.658 e - o.677 B • 0.692 B • 0.696 B • 0.705

NGI rating 500 T • ·0. 140 T • ·0.099 T • ·0.067 T • ·0.059 T • -o.040

VERY GOOO QUALITY ROCK MASS .. - 3.5 m • 5.0 m • 7.5 •• 8.5 ... 12. 5 Tightly inter!ooking ""'1is- s - o. 1 5 - 0.1 5 .. 0.1 :!. ... 0.1 ' . 0.1 tw>bed rock IJith """"atlwr- A • 0.651 A• 0.739 A• 0.848 A• 0.883 A• 0.998 sd jt7int.s at •Jm. CSIR rating 85 B • 0.679 B • 0.692 B • 0.702 B • 0.705 e-0.712

NGI rating 100 T • ·0.028 T • -0.020 T • ·0.01) T • -0.012 T • -0.008

GOOD QUALITY ROCK HASS m • 0.1 "' • 1.0 m • 1.5 m • 1.7 .. - 2.5 l're•h to sti!Jhtiy woatlwNd • - 0.004 s • 0.004 ' • 0.004 ' - 0.004 s • O.OO!i reek, • i41htt11 diotw>bed A• 0.)69 A • 0.427 A• 0.501 A• 0.525 lirith Joint• at J ta Jm. A• 0.603 CSlfl r'.;,ting 65 B • 0.669 B • 0.68) B - 0.695 B • 0.698 8. 0.707 NGI ratfrtg 10 T • -0.006 T • ·0.004 T • ·0.003 T • •0.002 T • ·0.002

FAIR QUALITY ROCK HASS m • 0.1 .. m • 0.20 m - 0. 30 .. * o.3i. m •_0.50 Ssvel'tJt oeto of model'<ltel11 I • 0.0001 5 • 0.0001 $ • 0.0001 • - 0.0001 5 • 0.0001 ""atlwl'fld joints •pao•d at A • 0.198 A - 0.2)4 A• 0.280 A • 0.295 A•0.346 O.J to lm. CSIR <atlng 44 B • 0.662 8 • 0.675 I • 0.688 B • 0.691 B•0.700

NGI <otlng 1.0 T • ·0.0007 T • ·0.0005 T • -0.0003 T • ·0.0003 T • -0.0002

POOR QUALITY ROCK HASS m - 0.04 m"" 0.05 "'. 0.08 .. - 0.09 llt • 0.1]

llum«-.. """'th<Nd Join ts •• 0.00001 • - 0.00001 •• 0.00001 I • 0.00001 •• 0.00001 at JO to ~0- IJith •- A• 0.115 A • 0. 129 A • 0.16? A• 0.172 A• 0.20)

""""" . d1'la» ...,.te f'O<>k. CSIR <>ting H B • 0.646 8 - 0.655 8. 0.672 B • 0.676 B • 0.686

NGI <atlng 0.1 T • ·0.0002 T • -0.0002 T • ·0. 0001 T • •0.0001 T • ·0.000I

VERY POOR QUALITY ROCK 1'ASS m • 0.007 m • 0.010 m - 0.015 Ill. 0.017 m • 0.025

""""'"""' hoavH11 ...,athored • • 0 • • 0 • • 0 I • 0 •• 0 Joint. -a • ~- ..ttlt A • 0.042 A • 0.050 A • 0.061 A • 0.065 A - 0.078 11""11• - ..... ts IJith , ......

CSIR <atlng ) I• 0.534 B • 0.539 •• 0.546 B • 0.548 B - 0.556

NGI roting 0.01 T • 0 T • 0 T • 0 T • 0 T - 0

. ---· ··--·~·----·-····-·-·~·---·· ·--····---~ ·-···--- .... ·----+·-----------------~

49 b() Q a;i

Jj m ;I.. cd a;i

.!:I

E1npirical Shear SLrengt.11 Relations Pclona Schist

2 c:J '-

- -· --·· --·--· --· ..

>< f" e u . '_·-_;_

/__ __ [J __ UJtir 1c1lc _ 0

1 5 ' -------··· ' -

1 D

I k>< k 8c [Jr- JWn

Ben 011

__ BCJttQn __ -- --------------+---

IJ) 5

D

Pet:J( ¢-::::35 .. c =.3.5J!sf

Ulfitn.a. = 32c C = /,O f(ef

ltssumed l?esdlkOLJ

¢ =28° c "" 0

I I '··· 10 20 25

Norrnal Stress KSF

1

1

1

** PCSTABL5M ** by

Purdue University

--slope stability Analysis-simplified Janbu, Simplified Bishop

or Spencer·s Method of Slices

Run Date: Time of Run: Run By: Input Data Filename: output Filename:

PROBLEM DESCRIPTION

BOUNDARY COORDINATES

10 Top Boundaries 10 Total Boundaries

1-24-91 7:51 AM CD B: 3775A01.GIN B: 3775A01. POU

SECTION A-A' GROSS STABL - INITIAL EARCH - TOE BELOW FAULT

s

Boundary X-Left Y-Left X-Right Y-Right Soil Type No. (ft) (ft) (ft) (ft) Below Bnd

1 .oo 190.00 130.00 192.00 1 2 130.00 192.00 200.00 210.00 1 3 200.00 210.00 280.00 245.00 1 4 280.00 245.00 400.00 249.00 1 5 400.00 249.00 885.00 440.00 1 6 885.00 440.00 1112.00 500.00 1 7 1112.00 500.00 1240.00 560.00 1 8 1240.00 560.00 2090.00 680.00 1 9 2090.00 680.00 2240.00 710.00 1

10 2240.00 710.00 3000.00 710.00 1

ISOTROPIC SOIL PARAMETERS

1 Type(s) of Soil

Soil Total saturated Cohesion Friction Pore Pressure Piez. Type Unit Wt. Unit Wt. Intercept Angle Pressure Constant Surface

No. (pcf) (pcf) (psf) (deg) Param. (psf) No.

1 135.0 135.0 500.0 30.0 .oo .o 0

A-·4-.J

/ ---~~~-

1

A Critical Failure Surface Searching Method, Using A Random Technique For Generating Circular Surfaces·, Has Been Specified.

160 Trial Surfaces Have Been Generated.

40 Surfaces Initiate From Each Of 4 Along The Ground Surface Between X =

and X -

Points 80.00

230.00

Equally Spaced ft.

Each Surface Terminates Between and

ft.

x = 800.00 ft. x =3000.00 ft.

Unless Further Limitations Were Imposed, The Minimum Elevation At Which A surface Extends Is Y = .oo ft.

100.00 ft. Line Segments Define Each Trial Failure surface.

Following Are Displayed The Failure Surfaces Examined. First.

Ten Most critical Of The Trial They Are Ordered - Most Critical

* * Safety Factors Are Calculated By The Modified Bishop Method * *

Failure Surface Specified By 14 Coordinate Points

Point x-surf Y-Surf No. (ft) (ft)

1 130.00 192.00 2 229.89 187.31 3 329.88 188.56 4 429.63 195.73 5 528.77 208.81 6 626.96 227.75 7 723.85 252.47 8 819.11 282.90 9 912.40 318.92

10 1003.38 360.42 11 1091.74 407.24 12 1177.18 459.21 13 1259.37 516.16 14 1331. 76 572.95

Circle Center At X = 259.0 • y = 1870.9 and Radius, 1683.9 '

*** 1.991 ***

Individual data on the 19 slices

Water Water Tie Tie Earthquake Force Force Force Force Force surcharge

Slice Width Weight Top Bot Norm Tan Hor Ver Load No. Ft(m) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg)

1 70.0 100567.6 .o .o .0 .o .o .o .o 2 29.9 115101.5 .o .o .o .o .o .o .0 3 50.1 313974.4 .o .o .o .o .o .o .o 4 49.9 387774.8 .o .o .o .o .o .o .o 5 70.1 537190.3 .o .o .o .0 .0 .0 .o 6 29.6 240625.3 • 0 .o .o .o .o .o .o 7 99.1 ******** .o .o .o .o .o .o .o 8 98.2 ******** .0 .o .o .o .o .o .o 9 96.9 ******** .o • 0 .o .o .o .o .o

10 95.3 ******** .o .o .o .o .o .o • 0 11 65.9 ******** .o • 0 .o .o .o .o . 0 12 27.4 480757.2 .o .o .o • 0 . 0 .o . 0 13 91.0 ******** • 0 .o .o . 0 .o .o . 0 14 88.4 ******** • 0 .o .o . 0 .o .o . 0 15 20.3 229492.2 . 0 . 0 . 0 .o .o .o .o 16 65.2 667742.8 . 0 .o • 0 .o .o • 0 .o 17 62.8 545344.9 . 0 • 0 .o . 0 • 0 • 0 .o

• 18 19.4 135787.8 .o . 0 .o • 0 • 0 • 0 . 0 19 72.4 227552.3 .o . 0 .o • 0 • 0 . 0 • 0



1 230.00 223.13 2 329.99 221. 77 3 429.82 227.66 4 528.96 240.76 5 626.88 261. 01 6 723.09 288.30 7 817. 06 322.48 8 908.32 363.39 9 996.37 410.79

10 1080.75 464.45 11 1157.06 521.12

Circle Center At X = 298,7 ; Y = 1601.2 and Radius, 1379.8

*** )

1


Point x-surf Y-Surf No. (ft) {ft)

1 130.00 192.00 2 230.00 191.79 3 329.91 196.04 4 429.53 204.73 5 528.67 217.85 6 627.12 235.36 7 724.70 257.25 8 821.20 283.45 9 916.45 313.93

10 1010.24 348,61 11 1102.39 387.44 12 1192.73 430,33 13 1281. 07 477.20 14 1367.23 527.95 15 1451.04 582.49 16 1463.75 591. 59

Circle Center At X - 185.0 ; Y = 2434.1 and Radius, 2242.7

*** 2.017 ***



1 180.00 204.86 2 279.39 215.92 3 378.37 230.17 4 476.84 247.60 5 574.69 268.19 6 671.84 291.91 7 768 .17 318.75 8 863.59 348.68 9 957.99 381. 66

10 1051. 29 417. 66 11 1143.37 456.64 12 1234.16 498.57 13 1323.55 543.39 14 1394.34 581. 79

Circle Center At X = -112.9 ; Y = 3292,9 and Radius, 3101.9

*** 2.023 *** )

1

A4.4

Failure surface Specified By 12 Coordinate Points

Point X-Surf Y-Surf No. (ft) (ft)

1 180.00 204.86 2 280.00 205.88 3 379.73 213.21 4 478.79 226.83 5 576.81 246.67 6 673.37 272.67 7 768.10 304.71 8 860.61 342.67 9 950.54 386.40

10 1037.54 435.72 11 1121.24 490.43 12 1171.04 527.68

Circle Center At X = 214.7 ; Y = 1780.9 and Radius, 1576.4

*** 2.029 ***



l 130.00 192.00 2 229.73 184.60 3 329.73 184.72 4 429.44 192.35 5 528.29 207.45 6 625.73 229.93 7 721. 20 259.67 8 814.18 296.50 9 904.12 340.21

10 990.52 390.55 11 1072.90 447.24 12 1150.79 509.96 13 1168.33 526.40

Circle Center At X - 278.2 ; Y = 1513.9 and Radius, 1330.1

• *** 2.048 ***

l


Point x-surf Y-Surf

A4.5

No, (ft) (ft)

1 130.00 192.00 2 229.87 186.82 3 329.83 189.37 4 429.31 199.62 5 527.69 217.51 6 624.41 . 242.93 7 718.87 275.75 8 810.52 315.75 9 898.81 362.70

10 983.22 416.33 11 1063.23 476.31 12 1080.85 491. 77

circle Center At X = 247,4 i y = 1477.6 and Radius, 1290.9

*** 2,049 ***


Point X-Surf '!-Surf No. (ft) (ft)

l 230.00 223.13 2 328.53 206.05 3 428.38 200.62 4 528.19 206.93 5 626.56 224.87 6 722.16 254.21 7 813.67 294.54 8 899.82 345.31 9 979.44 405.82

10 1051. 43 475.23 11 1060.58 486.41

Circle Center At X = 424,6 i Y = 1053.2 and Radius, 852.6

*** 2.061 ***

l

• Failure Surface Specified By 10 Coordinate Points

Point X-Surf 'l-Surf No. (ft) (ft)

l 230.00 223.13 2 328.35 205.05 3 428.18 199.22 4 527.97 205.74

1

•

5 6 7 8 9

10

626.19 721. 36 812.01 896,77 974.35

1038.58

224.51 255.23 297.45 350.51 413.61 480.59

Circle Center At X = 425.4 ; Y = 1008.0 and Radius, 808.8

*** 2,070 ***



1 130.00 192.00 2 228.98 177.76 3 328.89 173.52 4 428.72 179.33 5 527.47 195.13 6 624.12 220.77 7 717.72 255.97 8 807.32 300.39 9 892.00 353.58

10 970.91 415.00 11 1040.09 480.99

circle Center At X = 321.0 ; Y = 1168.6 and Radius, 995.l

*** 2.093 ***

y A x I s F T

.00 375.00 750.00 1125.00 1500.00 1875.00

x .oo +----*----+---------+---------+---------+---------+ . * ..4*

- ..• 12* - •• " • 12

375.00 + ..... 4* ••••• 12 • .•••• 914 ....... 4 .••••• 12 • ........ 54.

A 750.00 ••••... 124

I •

• • • 12 .. ..47.* .312 ..

. 312 .. .. 127

x 1125.00 • • • • • .3.4*6 .31.2 •

• 31* .41 .. .3.4

• • • .3 I 1500.00 +

•

• s 1875.00 +

• •

* ..

2250.00 + *

• F 2625.00 +

T 3000.00 + * ...

l - -·

1

)<

1

1

** PCSTABL5M ** by

Purdue University

--Slope stability Analysis-Simplified Janbu, Simplified Bishop



PROBLEM DESCRIPTION



1-24-91 8:07 AM CD B:3775A03.GIN B:3775A03.POU

SECTION A-A' GROSS STABL - INITIAL SEARCH - TOE ABOVE FAULT

Boundary X-Left Y-Left X-Right Y-Right Soil Type No. (ft) (ft)

1 .00 190.00 2 130.00 192.00 3 200.00 210.00 4 280.00 245.00 5 400.00 249.00 6 885.00 440.00 7 1112.00 500.00 8 1240.00 560.00 9 2090.00 680.00

10 2240.00 710.00


1 Type(s) of soil

Soil Total Saturated Type unit wt. unit wt.

No. (pcf) (pcf)

1 135.0 135.0

Cohesion Intercept

(psf)

500.0

(ft)

130.00 200.00 280.00 400.00 885.00

1112.00 1240.00 2090.00 2240.00 3000.00

Friction Angle (deg)

30. 0

(ft) Below Bnd

192.00 210.00 245.00 249.00 440.00 500.00 560.00 680.00 710.00 710.00

Pore Pressure

Param.

Pressure Constant

(psf)

.oo .o

1 1 1 1 1 1 1 1 1 1

Piez. Surface

No.

0

1

A Critical Failure surface Searchinq Method, Using A Random Technique For Generating Circular Surfaces, Has Been Specified.

200 Trial surfaces Have Been Generated.

40 surfaces Initiate From Each Of 5 Points Along The Ground Surface Between X m 300.00

and X = 500.00

Equally ft. ft.

Each Surface Terminates Between and

x = 800.00 ft. x -3000.00 ft.

Spaced

_VnJ.ess.'f'urther Limitations Were Imposed, The Minimum Elevation At Which A Surface Extends Is Y = .oo ft.

100.00 ft. Line Segments Define Each Trial Failure Surface.

Followinq Are Displayed The Failure surfaces Examined. First.

Ten Most Critical Of The Trial They Are Ordered - Most Critical



Point x-surf Y-surf No. (ft) (ft)

1 400.00 249.00 2 499.72 256.47 3 598.34 273.06 4 695.01 298.64 5 788,92 332.99 6 879.29 375.81 7 965.34 426.76 8 1040.37 481.07

circle Center At X = 369,2 • y - 1333.5 and Radius, 1085.0 •

*** 1.888 ***


AE1.~

Water Water Tie Tie Earthquake Force Force Force Force Force Surcharge

Slice Width Weight Top Bot Norm Tan Hor Ver Load No. Ft(m) Lbs(kq) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs{kg) Lbs{kg) Lbs(kg)

1 99.7 214090.1 .o .0 .o .o .o .o .o 2 98.6 571488.2 .0 .o .0 .o .o .o .o 3 96.7 786911.l • 0 .o .o .o .o .o .0 4 93.9 860376.3 .o .o .o .o .o .o .o 5 90.4 799754.6 .o .o .0 .o .o .o .o 6 5.7 47317.7 .o .0 .o .o .o .o .o 7 80.3 516686.2 .o .o .o .o .o • 0 .o 8 75.0 174596.6 .o .o .o .o .o .o .o



1 400.00 249.00 2 499.36 260.34 3 597.39 280.09 4 693.38 308.11 5 786.64 344.20 6 876.49 388.10 7 962.28 439.48 8 1008.13 472.55

circle Center At X = 319.l ; Y = 1407.9 and Radius, 1161.8

*** 1.891 ***

1


Point x-surf Y-Surf No. (ft) {ft)

1 350.00 247.33 2 449.82 241.26 3 549.45 249.79 4 646.78 272.76 5 739.72 309.67 6 826.28 359.73 7 904.63 421.87 8 933.75 452.89

circle Center At x = 442.1 ; Y ~ 917.6 and Radius, 676.6

*** 1.893 ***

A5.s



1 400.00 249.00 2 499.91 253.22 3 599.30 264.27 4 697.70 282.09 5 794.64 306.61 6 889.69 337.71 7 982.38 375.25 8 1072.28 419.04 9 1158.97 468.88

10 1242.05 524,54 11 1298.53 568.26

Circle Center At X = 388.4 ; Y - 1708,9 and Radius, 1459.9

*** 1.904 ***

1



1 500.00 288.38 2 599.81 294.59 3 697.68 315.10 4 791.58 349.49 5 879.55 397.04 6 959.76 456.76 7 963.85 460.84

Circle Center At X = 507.0 ; y ~ 981.1 and Radius, 692.8

*** 1.942 ***



1 300.00 245.67 2 399.01 231.62 3 499.0l 230.79

1

1

4 5 6 7 8 9

598.23 694.95 787.46 874.13 953.45

1008.52

243.19 268.60 306.58 356.45 417.35 472.65

Circle Center At X = 455.3 ; Y - 984.1 and Radius, 754.6

*** 1.946 ***



1 500.00 288.38 2 599.95 291.50 3 697.49 313.53 4 789.08 353.68 5 871.39 410.48 6 905.72 445.48

circle Center At X = 535.2 ; Y = 799.9 and Radius, 512.8

*** 1.954 ***



1 400.00 249.00 2 499.04 235.15 3 598.78 242.27 4 694.84 270.05 5 782.99 317.28 6 859.34 381.86 7 909.28 446.42

Circle center At X - 515.2 : Y = 711.3 and Radius, 476.5

*** 1.966 *** ) I I

..

1



1 350.00 247.33 2 448.52 230.21 3 548.49 232.90 4 645.95 255.29 5 737.07 296.49 6 818.24 354.89 7 886.28 428.18 8 895.16 442.69

Circle Center At X = 485.2 ; y = 728.5 and Radius, 499.8

*** 1.967 ***



1 350.00 247.33 2 448.12 228.05 3 548.ll 229.37 4 645.69 251. 25 5 736.67 292.76 6 817.16 352.10 7 883.71 426.74 8 892.44 441.97

Circle Center At X = 491.8 ; y = 705.3 and Radius, 479.5

*** 1.987 ***

y A x I s F T

.00 375.00 750.00 1125.00 1500.00 1875.00

x .00 +----·----+---------+---------+---------+---------+ * * * 6

375.00 + .6* .•• 3.

T 3000.00 + *

1

1

1

** PCSTABL5M ** by

Purdue University



Run Date: Time of Run: Run By: Input Data Filename: Output Filename:

PROBLEM DESCRIPTION



1-24-91 8:28 AM CD B:3775A07.GIN B:3775A07.POU

SECTION A-A' GROSS STABL - DETAILED SEARCH - TOE BELOW FAULT


1 .oo 190.00 2 130.00 192.00 3 200.00 210.00 4 280.00 245.00 5 400.00 249.00 6 885.00 440.00 7 1112.00 500.00 8 1240.00 560.00 9 2090.00 680.00

10 2240.00 710.00


1 Type(s) of Soil

Soil Total Saturated Type Unit Wt, Unit Wt.

No. (pcf) (pcf)

1 135.0 135.0

cohesion Intercept

(psf)

500.0

(ft)

130.00 200.00 280.00 400.00 885.00

1112.00 1240.00 2090.00 2240.00 3000.00


30.0

(ft) Below Bnd

192.00 210.00 245,00 249.00 440.00 500.00 560.00 680.00 710.00 710.00

Pore Pressure

Param.

Pressure Constant

(psf)

.oo .o

l 1 1 l 1 1 1 1 1 l

Piez. Surf ace

No,

0

1

A Critical Failure Surface Searching Method, Using A Random Technique For Generating Circular Surfaces, Has Been Specified.

200 Trial surfaces Have Been Generated.

200 Surfaces Initiate From Each Of 1 Points Equally Spaced Along The Ground Surface Between X - 130.00 ft.

· and X = 130.00 ft.

Each surf ace Terminates Between and

x .. 800.00 ft. x -1500.00 ft.

Unless Further Limitations Were Imposed, The Minimum Elevation At Which A Surface Extends Is Y = .oo ft.

100.00 ft. Line Segments Define Each Trial Failure Surface.






1 130.00 192.00 2 230.00 191. 71 3 329.86 196.91 4 429.29 207.58 5 527.99 223.69 6 625.65 245.19 7 721.98 272.01 8 816.70 304.09 9 909.52 341.31

10 1000.15 383.57 11 1088,32 430.74 12 1173.78 482.67 13 1256.26 539.22 14 1292.98 567.48

circle Center At X = 186;:1; • y--= 2007.2 and Radius, 1816.0 •

*** 1.990 ***


Water water Tie Tie Earthquake Force Force Force Force Force surcharge

Slice Width Weight Top Bot Norm Tan Hor Ver Load No. Ft(m) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs (kg) Lbs(kg) Lbs(kg)

l 70.0 86008.4 .o .o .o .o .0 .o .o 2 30.0 100476.7 .0 .o .o .o .o .o .o 3 50.0 277096.6 .o .o .o .o .o .o .o 4 49.9 338077.2 .o .o .o .o .o .o .0 5 70.l 446527.2 .0 .o .o .o .o .o .o 6 29.3 192842.6 .o .o .o .o .o .o ,0 7 98.7 857221.4 .o .o .0 .o .0 .o . 0 8 97.7 ******** .o .o .o .o .o .o .o 9 96.3 •••••••• .o .o .o .o .o .o .o

10 94.7 ............ .o • 0 .o .o .o .0 • 0 11 68.3 ******** .o .o .o .o .o .o .o 12 24.5 353610.9 . 0 .o .o .o .o .o • 0 13 90,6 ******** .o .o .o .o .o .o . 0 14 88.2 892028.6 .o .o . 0 .o .o . 0 • 0 15 23.7 188386.4 .o .o .o .o .o .o .o 16 61.8 421850.7 .o .o .0 .o .o .o .o 17 66.2 349600.4 .o • 0 .0 .o .0 .o .o 18 16.3 60354.3 . 0 .o .o .o .o .o .o 19 36.7 57198.5 . 0 .o .o .o .o • 0 • 0

Failure Surf ace Specified By 15 Coordinate Points

Point x-surf ¥-Surf No, (ft) (ft)

l 130.00 192.00 2 229.99 193.36 3 329.81 199.34 4 429.25 209.93 5 528.09 225.10 6 626.13 244.82 7 723.15 269.05 8 818.95 297.74 9 913.31 330.82

10 1006.05 368.23 11 1096.96 409.89 12 1185.85 455.70 13 1272.53 505.58 14 1356.81 559.40 15 1387.07 580.76

Circle Center At X = 150,6 • y = 2355.2 and Radius, 2163.3 •

..... 1.990 ***

A6.3

J.



1 130.00 192.00 2 229.88 187.19 3 329.87 188.60 4 429.58 196.23 5 528.63 210.04 6 626.62 229.98 7 723.18 255.97 8 817.94 287.92 9 910.53 325.70

10 1000.59 369.17 11 1087.77 418.15 12 1171.74 472.45 13 1252.17 531.87 14 1294.90 567.75

Circle Center At x = 257.7 ; Y = 1789.5 and Radius, 1602.6

*** 1.995 ***



1 130.00 192.00 2 229.73 199.33 3 329.07 210.80 4 427.85 226.38 5 525.90 246.04 6 623.04 269.76 7 719.12 297.50 8 813.96 329.19 9 907.41 364.80

10 999.30 404.26 11 1089.47 447.50 12 1177.76 494.44 13 1264.04 545.0l 14 1300.65 568.56

Circle Center At X = 4.7 ; y = 2589,6 and Radius, 2400.9

*** 2.011 ***

1



1 130.00 192.00 2 229.53 201.68 3 328.68 214.70 4 427.33 231.05 5 525.38 250.71 6 622.71 273.66 7 719.22 299.87 8 814.78 329.32 9 909.30 361.97

10 1002.67 397.78 11 1094.78 436.71 12 1185.53 478.72 13 1274.81 523.76 14 1362.53 571. 78 15 1374.77 579.03

Circle Center At X = -107.6 1 Y = 3153.1 and Radius, 2970.6

*** 2.018 ***



1 130.00 192.00 2 230.00 192.09 3 329.90 196.49 4 429.52 205.20 5 528.68 218.20 6 627.17 235.46 7 724.84 256.95 8 821.48 282.64 9 916.93 312.47

10 1011.00 346.39 11 1103.52 384.33 12 1194.32 426.24 13 1283.22 472.02 14 1370.07 521.59 15 1454.70 574.86 16 1482.79 594.28

Circle Center At X = 178.6 : y = 2504.3 and Radius, 2312.8

*** 2.026 ***

1



1 130.00 192.00 2 229.62 183.25 3 329.58 180.39 4 429.53 183.43 5 529.13 192.37 6 628.03 207.16 7 725.89 227.76 8 822.35 254.09 9 917.10 286.07

10 1009.80 323.59 11 1100.12 366.50 12 1187.76 414.67

--13 1272.40 467.93 14 1353.75 526.08 15 1428.69 586.64

circle Center At X = 328.0 ; Y = 1875.0 and Radius, 1694.6

*** 2.026 ***


Point x-surf Y-Surf NO. (ft) (ft)

1 130.00 192.00 2 229.34 203.51 3 328.27 218.08 4 426.70 235.70 5 524.55 256.35 6 621. 71 280.02 7 718.09 306.68 8 813.60 336.30 9 908.15 368.86

10 1001.65 404.33 11 1094.01 442.66 12 1185.14 483.83 13 1274.96 527.80 14 1363.37 574.52 15 1370.14 578.37

circle Center At X - -192.7 : Y ~ 3412.2 and Radius, 3236.3

*** 2.035 ***

l}G.t ~ - ·-··· -·~ -

1

Failure surface Specified By 16 coordinate Points


1 130.00 192.00 2 229.60 200.97 3 328.87 213.00 4 427.73 228 •. 09 5 526.07 246.23 6 623.80 267.39 1 720.84 291. 56 8 817.08 318.71 9 912.44 348.82

10 1006.83 381. 86 11 1100.15 417. 79 12 1192.31 456.59 i:r 1283.24 498.21 14 1372.84 542.62 15 1461. 02 589.77 16 1464.33 591.67

Circle Center At X = -110.4 ; Y = 3421.9 and Radius, 3238.9

*** 2.038 ***



1 130.00 192.00 2 229.86 186.70 3 329.84 188.49 4 429.45 197.37 5 528.18 213.28 6 625.53 236.14 1 721. 01 265.85 8 814 .15 302.25 9 904.48 345.16

10 991.53 394.37 11 1074.89 449.62 12 1154.11 510.63 13 1175.73 529.88

Circle Center At X - 254.6 : Y = 1596.6 and Radius, 1410.2

*** 2.041 ***

' .

1

..

y A x I s F T

.oo 375.00 750.00 1125.00 1500.00 1875.00

x .oo +----·----+---------+---------+---------+---------+ * . . *

.1. * - •.• 14

375.00 +.. * - ••• 31 • ••..• 714 • • • • - ..... 31 . • • • • • ... . . 8 .

A 750.00 +, •••• 714 .. . . . . • • • 714 .. - ........ 0 . • *

..... 614 . . - •..••.. 614 . .

. . . . . • • • 14 • x 1125.00 + ••••• 625*0

•••.... 6210 ...... 721*

...•• 6 .1 .••. 62 .

• • • 67 I 1500.00 + •• 6

s 1875.00 +

2250.00 +

F 2625.00 +

T 3000.00 +

*

*

*

. - ...

1

1

l

** PCSTABL5M ** by

Purdue University

--Slope Stability Analysis-simplified Janbu, Simplified Bishop

or Spencer"s Method of Slices

Run Date: Time Of Run: Run By: Input Data Filename: Output Filename:

PROBLEM DESCRIPTION



1-24-91 8:36 AM CD B:3775A08.GIN B:3775A08.POU

SECTION A-A' GROSS STABL - DETAILED SEARCH - TOE ABOVE FAULT


1 .oo 190.00 2 130.00 192.00 3 200.00 210.00 4 280.00 245.00 5 400.00 249.00 6 885.00 440.00 7 1112.00 500.00 8 1240.00 560.00 9 2090.00 680.00

10 2240.00 710.00


l Type(s) of Soil

Soil Total Saturated Type Unit wt. Unit wt.

No. (pcf) (pcf)

1 135.0 135.0

Cohesion Intercept

(psf)

500.0

(ft)

130.00 200.00 280.00 400.00 885.00

1112.00 1240.00 2090.00 2240.00 3000.00


30.0

(ft) Below Bnd

192.00 210.00 245.00 249.00 440.00 500.00 560.00 680.00 710.00 710.00

Pore Pressure

Param.

Pressure Constant

(psf)

.oo .o

1 1 l l 1 l 1 1 l 1

Piez. Surf ace

No.

0

•

1

A Critical Failure Surface Searching Method, Using A Random Technique For Generating circular Surfaces, Has Been Specified.

200 Trial Surfaces Have Been Generated.

200 Surfaces Initiate From Each Of Alonq The Ground Surface Between X

and X

1 Points = 400.00 .. 400.00

Equally ft. ft •

Each Surf ace Terminates Between and

x = 800.00 ft. x -1500.00 ft.

Spaced

Unless Further Limitations Were Imposed, The Minimum Elevation At Which A Surface Extends ls Y = .oo ft.

100.00 ft. Line Seqments Define Each Trial Failure Surface.






1 400.00 249.00 2 499.81 255.21 3 598.20 273.07 4 693.82 302.35 5 785.34 342.63 6 871.52 393.37 7 951.15 453.86 8 956.32 458.85

circle Center At X = 397.7 : Y - 1097.4 and Radius, 848.4


Water Water Tie Tie Earthquake Force Force Force Force Force Surcharge

Slice Width Weight Top Bot Norm Tan Hor Ver Load No. Ft(m) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg) Lbs(kg)

1 99,8 222986.6 ,0 .0 .o .o .o .o .0 2 98.4 578338.8 .o .o .o .o .o .0 .o 3 95.6 750902.0 .0 .o .o .o .o .o .o 4 91.5 744334.9 .o .o .o .o .o .o .o 5 86.2 578396.9 .o .o .o .o .o .o .o 6 13.5 70722.4 .o .o .o .o .o .o .o 7 66.1 178626.0 .o .o .o .o .o .o .o 8 5.2 1265.0 .o .o .o .o .o .o . 0



1 400.00 249.00 2 499.72 256.47 3 598.02 274.81 4 693.73 303.82 5 785.67 343.13 6 872.76 392.28 7 953.94 450.68 8 965.79 461. 35

Circle Center At X = 383.1 ; y = 1154.0 and Radius, 905.1 •

• •• 1.870 •••

1



1 400.00 249.00 2 499.77 255.86 3 597.98 274.69 4 693.20 305.22 5 784.05 347.01 6 869.21 399.44 7 937.56 453.89

circle Center At X = 393.2 ; y = 1077.2 and Radius, 828.2

••• 1.871 •••

l



1 400.00 249.00 2 499.91 253.36 3 598.27 271.37 4 693.24 302.70 5 783.01 346.74 6 865.90 402 .69 7 916.89 448.43

Circle Center At X = 418.3 • y = 976.5 and Radius, I

*** 1.873 ***


Point X-Surf Y-surf No. (ft) (ft)

1 400.00 249.00 ·2 499.72 256.42

3 598.26 273.45 4 694.70 299.92 5 788.12 335.59 6 877.65 380.13 7 962.46 433.12 8 1016.72 474.82

Circle Center At X = 374.9 ; y - 1272.7 and Radius,

*** 1.880 ***


Point No.

1 2 3 4 5 6 7

X-Surf (ft)

400.00 499.36 597.09 692.22 783.82 870.96 950.30

Y-Surf (ft)

249.00 260.34 281.52 312.33 352.46 401. 51 457.26

727.7

1024.0

..

circle Center At x = 336.l ; Y - 1249.6 and Radius, 1002.7

*** 1.887 ***

l



1 400.00 249.00 2 499.36 260.29 3 597.35 280.25 4 693.21 308.73 5 786.20 345.51 6 875.60 390.31 7 960.74 442.77 8 996.65 469.51

circle Center At X = 323.8 ; y = 1372.8 and Radius, 1126.3

*** 1.888 ***



1 400.00 249.00 2 499.98 247.12 3 599.38 258.09 4 696.55 281. 71 5 789.89 317.60 6 877.85 365.16 7 958.99 423.61 8 1012.42 473.68

circle Center At x = 465.2 : Y = 1018.2 and Radius, 771.9

• *** 1.890 ***

l

Failure Surface specified By 9 coordinate Points

·. .. Point x-surf Y-surt

No. (ft) (ft)

1 400.00 249.00 2 499.91 253.22 3 598.97 266.91 4 696.28 289.94 5 790.96 322.12 6 882.16 363.14 7 969.05 412. 64 8 1050.85 470.16 9 1073.96 489.94

circle Center At x = 405.6 ; Y - 1300.7 and Radius, 1051.7

*** 1.899 ***



1 400.00 249.00 2 500.00 248.91 3 599.39 259.90 4 696.96 281. 85

• 5 791.48 314.47 6 881. 81 357.38 7 966.82 410.04 8 1045.47 471.80 9 1060.26 486.32

circle Center At X = 450.8 ; Y ~ 1148.1 and Radius, 900.5

*** 1.901 ***

1

y A x s F T

.00 375.00 750.00 1125.00 1500.00 1875.00

• x .oo +----*----+---------+---------+---------+---------+ * * *

375.00 + * •• 1

••

• • • • • • .16

• • • .1 • A 750.00 +. • •

• • • 81. .13*

• • .81 .·91111 5

• • • .9 x 1125.00 + • • * •

• • • • • • • *

• • • • • • •

I 1500.00 + •

s 1875.00 +

*

2250.00 + *

•

F 2625.00 +

T 3000.00 + * ....

•

•

l

•

1

•

** PCSTABL5M ** by

Purdue University


or Spencer's Method of Slices


PROBLEM DESCRIPTION



2-1-91 10:52 am CD a:3775a30.in a:3775a30.out

SECTION A-A' GROSS STABL - SEISMIC


1 .00 190.00 2 130.00 192.00 3 200.00 210.00 4 280.00 245.00 5 400.00 249.00 6 885.00 440.00 7 1112.00 500.00 8 1240.00 560.00 9 2090.00 680.00

10 2240.00 710.00


l Type(s) of Soil

Soil Type

No.

1

Total Saturated unit wt. unit wt.

(pcf) (pcf)

135.0 135.0

Cohesion Intercept

(psf)

3000.0

(ft)

130.00 200.00 280.00 400.00 885.00

1112.00 1240.00 2090.00 2240.00 3000.00


35.0

(ft) Below Bnd

192.00 210.00 245.00 249.00 440.00 500.00 560.00 680.00 710.00 710.00

Pore Pressure

Param.

Pressure Constant

(psf)

.oo .o

1 1 1 l 1 1 1 1 1 1

Piez. surf ace

No.

0

•

1

•

l

•

A Horizontal Earthquake Loading Coefficient Of .soo Has Been Assigned

A Vertical Earthquake Loading Coefficient Of .250 Has Been Assigned

Cavitation Pressure = .o psf

Trial Failure Surface Specified By 14 Coordinate Points


1 130.00 192.00 2 230.00 191.71 3 329.86 196.91 4 429.29 207.58 5 527.99 223.69 6 625.65 245.19 7 721.98 272.01 8 816.70 304.09 9 909.52 341. 31

10 1000.15 383.57 11 1088.32 430.74 12 1173.78 482.67 13 1256.26 539.22 14 1292.98 567.48

Circle Center At X = 186.1 ; y - 2007.1 and Radius, 1816.0

Factor Of Safety For The Preceding Specified Surface = 1.100

WARNING - Factor Of Safety Is Calculated By The Modified Bishop Method. This Method Is Valid Only If The Failure Surface Approximates A Circle.

x

.Y A x I s F T

.00 375.00 750.00 1125.00 1500.00 1875.00

.00 +----*----+---------+---------+---------+---------+

375.00 +

* *

s * s

s s *

s

A 750.00 + s s

* s s s

x 1125.00 + * s

S* s

I 1500.00 +

s 1875.00 +

*

2250.00 + *

• F 2625.00 +

T 3000.00 + * 1

Trial Failure Surface Specified By 8 Coordinate Points

Point x-surf Y-Surf No • (ft) (ft)

• 1 400.00 249.00 2 499.81 255.21

• 3 598.20 273.07 4 693.82 302.35 5 785.34 342.63 6 871.52 393.37 7 951.15 453.86 8 956.32 458.85

Circle Center At X = 397.7 : y = 1097.4 and Radius, 848.4

ft/313

1

•

•

•

Factor Of Safety For The Preceding Specified Surface = 1.367

WARNING - Factor Of Safety Is Calculated By The Modified Bishop Method. This Method Is Valid Only If The Failure Surface Approximates A Circle.

y A x I s F T

.00 375.00 750.00 1125.00 1500.00 1875.00

x .00 +----*----+---------+---------+---------+---------+ * * *

375.00 + *

A 750.00 +

x 1125.00 +

I 1500.00 +

s 1875.00 +

2250.00 +

F 2625.00 +

s

s s

s s *

s

* *

*

*

I i .;

I • •

T 3000.00 +

•

,

' ' OVERSIZED -~·

DOCUMENT HAS BEEN PULLED AND SCANNED WITH THE MAP

FILE.

. - . . '

. ,' ·'· ~'' .

--Since 1956


Corporal!;' ()ffi(E": 15414 (Jbrito Rodd, Umr A, Van Nuy~, CA 91401) • (81 BJ 989-53.18 • 26545·82 Feliii:. V.:ildc.z Avenue, R:anchaCaliforniJ, CA 91390 • !71 4! b7b-8JB2

September 18, 1991

The Old Wrightwood Ranch, Inc. c/o Spindler Engineering 7120 Hayvenhurst Avenue, Ste. 200 Van Nuys, CA 91406

Attention: Mr. Larry Gray

Subject: DEBRIS FLOW Lots 1, 2 and 3, Tract 45783 Wrightwood Area Los Angeles County, California

Dear Mr. Gray:

Job No.: 3775-05 Log No.: 18677

On August 6, 1991, we prepared a response to concerns raised in the Los Angeles County Geotechnical Review Sheet dated June 19, 1991. In that response, we stated that debris would be diverted to the private driveways.

The total distance from the slough walls to the private driveway and then to the County road (Logwood Drive) varies from 400 to 600 feet. Therefore, it is our opinion that a possible debris flow will not adversely affect the County road.

If you have any questions concerning this letter, please do not hesitate to contact this office.

Very truly yours, RSA ASSOCIATES, INC.

- -

Edward Barton, R.G.E.

EB:el



Since 1956 RSA Associates, Inc.

Corporitlt' Office; 15414 Cabrilo Rucld, Ul"lil A, Van Nuys, CA 9140b •(618) qgq_5335 • l6S45-B:! Felix Valdi?.l AveruJe. Rancho California, CA 92390• l7 l 4J676-8l82

August 22 1 1991 Job No.: 3775-05 Log No.:_ 18616

\~~ L~~~ ~ ~~ ® ·, . SE? G ~ '991 The Old Wrightwood Ranch, Inc.

c/o Spindler Engineering 7120 Hayvenhurst Avenue, Ste. 200 Van Nuys, CA 91406

Attention: Mr. Larry G. Gray

PROCtti~11111.:i 1.itNll:R Lf\NO OE.V. Q\V.

Subject: RESPONSE TO COUNTY GEOTECHNICAL ENGINEERING REVIEW LETTER DATED JUNE 19, 1991 AND COUNTY GEOLOGIC REVIEW LETTER DATED JUNE 26, 1991 Lots 1, 2 and 3, Tract 45783 (formerly a part of Tract 41777) Wrightwood Area Los Angeles County, California

Dear Mr. Gray:


Los Angeles county Geotechnical Engineering Review Sheet

dated June 19, 1991 and the Los Angeles Geologic Review Sheet

dated June 26, 1991,

L.A. COUNTY GEOTECHNICAL ENGINEERING:

1. As previously requested, show the following on the

geotechnical map.

a. Existing and proposed grades.

b. The area and overexcavation depth required for

soils subject to hydroconsolidation and for

slopewash and alluvial material.

c. Location of private sewage disposal system.

d. Restricted Use Area.



Job No.: 3775-05 Log No.: 18616 Page 2

RSA:

The Geologic Map dated August 8, 1991 is attached.

a. The existing grades and the proposed grades for the

private driveways are shown on the map. The exact

locations and grades of the houses has not, to our

knowledge, been determined.

b. As noted in the report, the site is mantled with

three feet or less of topsoil. In our report dated

January 4, 1988 we recommended that the existing

topsoil, slopewash and weathered bedrock within the

proposed development areas should be removed and

recompacted. The area of removal shal1 extend

beyond the edge of footing at least 3 feet or equal

to the depth of removal, whichever is greater.

When the building sites are determined, a grading

plan showing the extent of removal and recompaction

should be prepared.

c. The approximate limits of possible disposal areas

has been transferred from our Plot Plan which

accompanied our report dated July 13, 1988 to the

attached Geologic Map.

d. The restricted use area is shown on the attached

Geologic Map.



Job No.: 3775-05 Log No.: 18616 Page 3

L.A. COUNTY GEOTECHNICAL ENGINEERING:

2, Debris flow may not be directed into street right of

way. Recommend appropriate mitigation. If the debris

flow is contained by slough walls, then recommend

catchment area to accommodate the debris flow.

RSA:

As noted in our letter dated January 31, 1991, the

volume of debris was computed to be 928 cubic yards and

would be diverted to the private driveways. If this

volume were evenly distributed, the depth of the debris

would be two feet or less.

•• L.A. COUNTY GEOTECHNICAL ENGINEERING: ••

3. Please include a copy of this [.eview sheet with your

response. •

RSA:

Comply.

L.A. COUNTY GEOLOGY:

1. Please provide a response to item 2 of previous geologic

review sheet dated 10/25/90.



RSA:

See answer to No. 1 above.

2. L.A. COUNTY GEOLOGY:

Job No.: 3775-05 Log No.: 18616 Page 4

The geotechnical Engineering Unit's requirements are

attached (review is dated 6/19/91).

RSA:

Comply.

This opportunity to be of service

If you have any questions

not hesitate to co ii .,.!his off· ':? 1·,;'.-' / , '

.. ~ ...... ·-.'!-

1242

EB/KWE:el

Enclosures: Geologic Map Copy of Geotechnical Engineering Review Sheet, dated June 19, 1991 and Geologic Review Sheet dated June 26, 1991



...., 1..1' .... - .... ~ • - - -

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KA.TE.RIALS fl«llHEERll«l PIVIS!OH Tl!.. (Ill) 458·49<3

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Action: _ Plin II geol091Qll)' lpprovod. k_ PIM II not '!'PfllVecl for r ... sans below. _ Plan 15*roved 9eologleal1)' •\lb.J•d ? st2141T PLAHS fat RECHECK. IDt;lYd• a copy

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GEOTECHNICAL ENGINEERING REVlflr/ SHEET

COUNTY OF LOS ANGELES Addre$s: 900 So. Fremont Ave. DEPARTMENT Of PUBLIC WORKS

Alhambra, CA 91803 Telephone: (816) 450~4926 Materials Engineering Div1s1on

UnBraded· S1te lots Tract 45783 Parent ~77 __ Location ~oOd Dr1v~htwood Deve1oper/~r 91~ Rffoh~od ·Ranch; Inc. Engineer S~1ndter ng neer JS cor~ Gaotechn1ca Engineer RSA ( .R. 3 ?s~o31 Geo10911t Same as above

Grading Plan Check No. 3968

Revtew of:

D1itrlct Off1ee e.o -Sheet 1 of l

DISTRIBUTION:

Drainage and Grading sect. ~Geo/Soils Central File ~ D1str1ct Engineer = Geolog1 st

Geotechn1cal Engineer - Engineer -

Geotechnical Report dated 1/31/91

Action:

Geo1og1c Report dated 1/31/91

Before approval for feas1b111ty the fo1tow1ng lnfonnatlon is required to assess the development 1$ $hown on the tentative map:

Remarks:

1, As prev1ous1y requested, show the following on the geotechn1ca1 map:

_1. ·Existing and proposed grades. b. The area and overexcavat1on depth required for soils subject to hydroconso1tdat1on . and for slope wuh and a11uv1a1 material. ' c. 'Location of private aewage disposal system. d. · Rutrfcttd Use Area. -

2. Debris flow may not be directed Into 1treet right of way. Recomnend appropriate mltJgation. If the debris flow is contained by $lOugh walls, then reconrnend catchment area to accomnodate the debris now.

·r 3. Please Include a cop,v of thU review sheet w1th you response • . ,

Date 6119/91

, Ok1ah Alhayek C:45783~

Documents

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