Draft-Work In Progress

GEOTECHNICAL REPORT

RAGGED MOUNTAIN DAM

Dra resS

Rivanna Water and Sewer Authority

August 19, 2008

Prepared by

[@g GannettFleming

List of Tables Table 1. Summary of drilling methods 9 Table 2. Description of a weathering profile for igneous and metamorphic rocks 13 Table 3. Summary of soil testing results 14 Table 4. Summary of rock testing results 16 Table 5. Characteristics of all borings 18 Table 6. Summary of all test pits ~ 19 Table 7. . Error! Bookmark not d''1f:~d.

Table 8. . Error! Bookmark 1;I(:ftd~ned. ~, ... ·t .~ .

....~~.~"j

· t f'Fi l -: IL . . IS ~ . ~gurestJi :~~j!i) Figure 1. Generalized geologic terrane map of virgirua ~.!'.!,4,'- 2 Figure 2. Structural cross section through the Blue Ridge Province in Central Vir~ini~~ 3 Figure 3. Geologic map of Albemarle County, Virginia (1962) ~ ..~~'l-::;i)!.~ 4 Figure 4. Geologic Map of Virginia (1993 ) i.~'~:~~ S"';~ 5 Figure 5. Bedrock exposure located on east abutment of proposed datpi: ...,; " I 6 Figure 6. Soils map ofthe Ragged Mountain Dam area l".~;;":~,.:';l.L 7 Figure 7. Nutating. disk w~ter meter and mecha~ical ~ressure fiui/ ~

r

11 Figure 8. Electronic field Instruments and real time display ll:

fL 11

Figure 9. Boring GF-22, soft zone from 34.0 - 44.0 ft .,.;~ 21 Figure 10. Boring GF-8, approximate depth 19.6 ft.:t:. .,;~\: ~~; 22 Figure 11. Boring GF-8, highly weathered zone, app~.imate depth 42.7 to 46.5 ft 23 Figure 12. Boring GF-8, typical core extracted from de~~s greater than 50 feet. 24 Figure 13. . ,,~ f. Error! Bookmark not defined. Figure 14. Figure 15

.. ~~

~."'i;~!-- -::

/t Error! Bookmark not defined. Error! Bookmark not defined.

Figure 16. .. ,::'.~;;..;.~!.: Error! Bookmark not defined. Figure 17. . ~\ j)••'i ../ Error! Bookmark not defined. Figure 18 " .: ..\ ~.~ Error! Bookmark not defined. F~gure 19. Typical :veath~ct~~I1ofjle for .metamorphic and intrusive igneous rocks 27 Figure 20. Weathenng profiles-incrystalline rock 27 Figure 21. Weathe~ing profl'le of granite 28 Figure 22. Depth 6fweathering as affected by rock composition, dikes and faults 29

l' ,k'~~_.Jj

\~~. .' List of Appendices Appendix A' GeQtclgical Mapping and Discontinuity Data . ." App~.n4~~:~\~6ring Logs Aprendix ~ 'Rock Permeability Test Data AppelJdixb Geophysical Survey Report Apperidi)"( E Test Pit Logs Appendix F Laboratory Test Results Appendix G Subsurface Profiles Appendix H Seismic Hazard Assessment Report

11

Ragged Mountain Dam -

Geotechnical Report

Project No. 48782

INTRODUCTION

This report outlines the subsurface investigation and analysis completed for the proposed new Ragged Mountain Dam, near Charlottesville, VA. Two separate field investigations were conducted between November 2007 and April 2008, Analyses and recommendations in this report were completed between January 2008 and July 2008.

1.0 GEOLOGY

1.1 Physiography

The site for the proposed new Lower Ragged Mountain Dam is 108'ated'within the Blue Ridge Physiographic Province. Figure 1 below shows Generalized Geofogic T~frtl.ne Map of the Blue Ridge and adjacent Western Piedmont Physiographic Provinces; More specifically the proposed dam site is located in the Northern Blue Ridge Su~prov,iriee:,,~hich is characterized as a rugged region with steep slopes, narrow ridges, broad mountains, and high relief.

tc· ••...•,J'

In Virginia, the Blue Ridge province forms a qasemerit massif with Mesoproterozoic crystalline rock in its core and Late Neoproterozoic tQ!Eatly Paleozoic cover rock on its flanks. The Blue Ridge province is allochthonous and h~S:"lJeen thrust to the northwest over Paleozoic rocks of the Valley and Ridge province. Although di-Jier deformation events are recorded in the older igneous and metamorphic rocks., the Blue Ridge is a contractional structure that experienced deformation and crustal short~ni,Qg during the Paleozoic.

The basement rocks of the Blut'R.idge include a diverse assemblage of granitoids and gneissic lithologies that were emplaced; in' thickened crust and locally metamorphosed at high­grade conditions about 1.0 .to i\2 &hH6n years ago during the Grenvillian orogeny (College of William and Mary, 20066l:'f-ate Neoproterozoic (750-700 Ma) granitoids intrude the Grenvillian rocks and areas~,~ciated with an early phase ofIapetan rifting. Late Neoproterozoic sedimentary rocks range from non-marine alluvial conglomerates to deep-water distal turbidites and are derived fro,er Grenvillian basement exposed along a rifted continental margin. In central and northern Virginia} the 570 Ma Catoctin metabasalts overlie the Late Neoproterozoic sedimentary units:'

1.2 Regional Structural Geology

Structurally, the Blue Ridge province is a large, eroded anticline overturned to the west as depicted in the cross section depicted by Figure 2. The proposed dam site is located within the Lovingston Massif just west of the unconformity between the Lynchburg Group which underlies much of the city of Charlottesville. The Robertson River batholith is located in the northern most part of the Blue Ridge and is not present in the area west of Charlottesville. The core of the anticline is composed of igneous and metamorphic rocks collectively known as the Grenville, although there arc also late Proterozoic intrusives and sediments present too. They are the oldest rocks in the state at 1.1 billion years and a protolith at 1.8 billion years.

l~i Gannett Fleming August 2008

Ragged Mountain Dam -

Geotechnical Report

Project No. 48782

Generalized

_Mz Mesozoic WestcUl, Chopawamsic Carolina

Basins PiedmQftt"'\ Volcanic Belt Slate Belt ~~" ,

Triassic sedrrnentary Proterozoic to Early Early Pale~zm~ Cambrian- Ordovician Neoproterozoic rocks deposited in Paleozoic rocks that meta- sedimentarY volcanic-plutonic rocks meta- volcanic, hal f grabens & formed in and on the andigneou~roc~ that formed in a volcanic plutonic, and grabens during rifting margin of ancient , associatedwith the arc outboard of North sedimentary rocks that produced the North America ,', ~ suture zone between America. Accreted that formed outboard Atlantic Ocean. (Laurentia) i·', ,,lllue Ridge during late Ordovician of North America

(Laurentian) rocks Taconic Orogeny, Post and terranes of the Taconic Piedmont metasedimentary rocks

Figure 1. Generalized geologic terrane map of virginia

Geologic Terrane Map of the Virginia

Piedmont & Blue Ridge l~i-:N, C.\-L ~tlli.f"ii, ClJlJt:,:.·lIfV.'''f'I~W''&.\fiJf.¥

a

OBR Owl'

Coastal Plain

[,;;i),j;1 cs Blue Ridge

t7t~1;41 GR Goochland

Raleigh Belt

Proterozoic rocks that may have formed in and on the margrn of ancient North America (Laurentia]. Overthrust by Chopawarnsic and Carolina Slate Belts Metamorphism during the Late Paleozoic

2 August 2008

PIEDMONT

PROVINCe

.:>'••..', •••• "' "-.

. "~ "',

'. '.', -, "..,.... -.,.",

"'>«'"

Ragged Mountain Dam ­ Project No. 48782

Geotechnical Report

Figure 2. Structural cross section through the Bll!el!idge Province in Central Virginia (after Fichter, L.S. antl.)Jae4¥e',"S.J. 2000)

:'.::;. ,,'

The east and west flanks of the anticline are much younger volcanics (Crossnore event) and clastic sediments. The clastic sediments fill rift grabens on the northwest and southeast flanks of the anticline (Lynchburg, Ocoee,Gt~h(rfather Mtn., Mt. Rogers Groups). Stratigraphic thicknesses range from about 3000 meters to 7000 meters. The final filling of the graben and creation of a divergent continental margin is preserved in the metamorphosed lava flows (Catoctin formation) and sedimentary rbcks (Chilhowee Group and Evington formation) about 570-600 million years old' '.

1.3 Site Geology

1.3.1 Bedro~kUnits

Nelson (t962) mapped the bedrock units at the proposed dam site as the Lovingston Formation (Figure 3). The Lovingston quartz monzonite commonly referred to as the l;ovingston Gneiss as it has developed varying degrees of gneissic structure it forms the Blue Ridge b'asement complex. According to Nelson (1962) the rock contains predominantly plagioclase, orthoclase feldspars, and as minor minerals, quartz with biotite mica and hornblende. According to the Geologic Map of Virginia (1993), ShOV-iO in Figure 4, the proposed dam site is underlain by a medium to coarse grained biotite granitoid gneiss and layered granitoid gneiss (Ybg). This unit is characterized as a mesocractic (containing 30 to 60 percent dark minerals) medium to coarse grained biotite-rich quartzofeldspathic gneiss.

l~f GannettFleming 3 August 2008

Ragged Mountain Dam ­ Project No. 48782

Geotechnical Report

Figure 3. Q~()16gic rtulP of Albemarle County, Virginia (1962) ,:'~_ ..•'"

; 1 •

According to NeTs6n(l,962) the Rockfish Conglomerate is mapped approximately 7,400 feet east of the proposed dam site. The Rockfish Conglomerate lies unconformably over the Lovingston Gneiss.' Since 1962 the Rockfish Conglomerate has been reclassified as a fanglomerate, amatrix-supported, poorly sorted pebbly to cobbly lithic conglomerate that occurs at the base of the Lynchburg Group (ZIf). The Rockfish Conglomerate is slightly overturned and dips about &0 degrees to the west, with the Lovingston Gneiss lying overturned on the Rockfish Conglomerate (Nelson, 1962). The Geologic Map of Virginia (1993) also shows the biotite­plagioclase augen gneiss that underlies the proposed dam site is intruded by a two-mica granite (Ymg). This intrusive unit is characterized as coarse grained, inequigranular muscovite-biotite two-feldspar gneiss.

[~! Gannett Fleming 4 August 2008

Ragged Mountain Dam - Project No. 48782

Geotechnical Report

,

~!~ur~, 4. Geologic Map of Virginia (1993) .-,~~..-- -.-,.: '.

Nelson (l962)rriapp~d amphibolite dikes, and diabase dikes that have intruded the Lovingston Gneiss. The amphibolite dikes are composed of crystalloblastic rock containing mostly amphibole and plagioclase. Quartz is typically absent or present in small quantities. Most of the amphibohtedikes trend in a northeast to southwest direction. Diabase dikes are of basaltic composition consistlng of labradorite and pyroxene and characterized by ophitic texture (Nelson, 1962).

. 1.3.2 Structural Features

The Geologic Map Albemarle County. Virginia (Nelson, (962) indicates a fault located approximately 1.5 miles east of the proposed dam site (see Figure 3). This fault is a well developed border fault typically found on edge of large massifs or batholiths. This fault dips steeply to the west and is well exposed on Route 29 west of Charlottesville, where the fault zone is approximately 50 feet and is comprised of biotite schist. This border fault can be traced southward into Amherst County. According to Nelson (1969) north of Charlottesville, the border fault roughly follows the contact between the Lovingston gneiss and the acid granite

i~1 6annett Fleming 5 August 2008

Ragged Mountain Dam - Project No. 48782

Geotechnical Report

which has replaced the Rockfish Conglomerate. The border fault crosses the Green County line to the north west of Piney Mountain.

Numerous normal faults striking northwest to southeast have been mapped approximately 12,000 feet northeast of the proposed dam site in the Charlottesville metro area (see Figure 3). According to Nelson (1962) one of these faults on the western side of Charlottesville offsets a northeast southwest trending normal fault a distance of 400 feet. .

No published discontinuity data were located in the vicinity of the propos.~d,d~i!l:' site therefore a bedrock discontinuity survey was completed on exposed natural outF,r6p~ (e.g., see Figure 5) in the area west and northwest of the existing Ragged Mountain Da9-l( Tne"~omplete discontinuity data report is included in this report in Appendix A. A total of.~vtprinciple joint sets were identified, four of the five sets strike north or northeast, the remain.iri,gjoint set strikes northwest and is nearly orthogonal to the other four joint sets. ....:

The joint sets identified in the site discontinuity SU~y~yeo,.g~Y~t~ well with published structural data. As previously mentioned, normal faults mapp,e~f nortHeast of the proposed dam site strike between N50W and N60W (see Figure 3). Joint/set 0 similarly strikes at N67W. Three northeast trending joint sets (A, C, and E) follow !pe north~ast to southwest trending Blue Ridge Basement Complex. r

Figure 5. Bedrock exposure located on east abutment of proposed dam

[~i GannettFleming 6 August 2008

1.3.3 Soils

According to the Web Soil Survey maintained by the Natural Resources Conservation Service the proposed dam site is underlain by the Chester very stony loam 25 to 45 percent slopes (15E) as depicted in Figure 6. Cobbles, stones or boulders typically cover approxil11gf:ly 7 percent of the surface area. The typical profile is 0 to 7 inches: Loam; 7 to 41 inches: ..t:lflY loam; 4\ to 79 inches: Loam. Chester very stony loam is characterized as residuum, ~eaTI1ered from granite and gneiss. The soil is well drained, and the depth to water table is i.n,exce,srof 80 inches. The permeability and water capacity are moderate, surface runoff is rapi~;arfQffie hazard of erosion is severe. The surface soil layer of the Chester very stonylo~;k:has a uses classification of CL.

100 200

500 1,000 2.000

714200 71... 00 ""'00

USOA Natural Resouc'Ces ... ccneervation Service

Sod Map-Albemarle County. VlC9in~ (Scie Map of the Lower Ragged Mountam Dam Area)

Web SOil Survey 2.0 National Cooperative Soil Survey

Figure 6. Soils map of the Ragged Mountain Dam area

!~16annettFleming 7 August 2008

Ragged Mountain Dam -

Geotechnical Report

Project No. 48782

2.0 GEOTECHNICAL INVESTIGATIONS

2.1 General

An initial geotechnical investigation was completed by Gannett Fleming, Inc. from November 2007 to January 2008. A subsequent investigation was completed from March to April 2008. The purpose of these investigations was to characterize the foundation cO!1ditiori~

for the design of the new Ragged Mountain Dam. The initial investigation consisted or~~rtY­two drilled boreholes, twelve excavated test pits, borehole video logging of select boreholes' and seismic refraction and MASW geophysical surveys. The second investigation conS,i~t~~ of four additional core borings located on the east and west abutment, and five boring~~mpreted along the Interstate 64 corridor. The information obtained during the drilling"a,long' 1-64 is not presented in this document and can be found in the 1-64 Investigation :Repqri./~epresentative samples of rock and soil have been selected for testing to determine the' eng~ne~Jifig properties of these materials. All borings and test pits completed at the proposed-dam site are shown on Figure B-1 in Appendix 8.'; .,'

2.2 Field Investigations

2.2.1 Borings

The boring programs for the new dam collectively consisted of twenty-six core borings. both vertical and angled (300 from vertic~I)~. that were drilled between November 13. 2007 and January 9, 2008 and between April 1, 2QOSand April 9 2008 by L.G. Hetager Drilling, Inc. of Punxsutawney, PA under the supervisiori'of Gannett Fleming, Inc. personnel. All borings Were drilled using custom drill rigs, ~designe& and built by L.G. Hetager Drilling, Inc. The rigs used were the Hetager 224 and 225 hacltrriounted rigs, and Hetager 231 rubber tired rig which are built specifically for use in fe~ottr areas with difficult access. Borings designated GF-2 through GF-IO and GF-20 and GP:'2L'are all located along the axis of the proposed dam, seven of which (GF-2 through GF-4, GF-:6, and GF-8 through GF-I0) are angled 300 from vertical to determine the impact of nearvertical rock joints present at the site on foundation design. All inclined borings are orientedparallel to the axis of the dam. Additionally, borings labeled GF-1, GF-12, GF-13, GF-18,GP"\9, GF-22 and GF-23 are located on the west abutment, borings GF-15, GF­20, GF-21, GF··24 and GF-25 are on the east abutment and borings GF-14 and GF-17 are located in the ar~a ofthe proposed stilling basin. All borings were advanced into rock before terminating at final depths ranging between 25 and 268 feet. Rock permeability testing was also completed in seventeen of the borings (GF-2 through GF-14 and GF-22 through GF-25).

Vertical boreholes for the dam site were advanced through overburden materials using 3.25 inch (in.) inner-diameter (10) steel casing or 4.25 in. hollow stem augers. Most vertical holes were continuously sampled using a 24 inch long, three inch outer-diameter (00) split­spoon sampler, which were driven by a 300 pound hammer, that was dropped a distance of 18 in. Blow counts, which are used as an indicator of soil density, were obtained by summing the blow counts for the second and third six in. intervals during driving. Split spoon sampling of inclined

[C~! Gannett Fleming 8 August 2008

boreholes was not completed because calibrated blow counts cannot be obtained. Therefore, these inclined holes were advanced through the overburden materials without sampling by spinning steel casing to the top of rock. Water was used as the drilling fluid to flush drill cuttings out of the hole. In both the vertical and the angled boreholes, rock coring was completed using a 3.16 in. 00 NX core bit, wireline NQ3 triple tube core barrel, and water as the drilling fluid. In this method. a sample recovery tube sits within two outer tubes whichare all allowed to spin freely of one another. The multiple tubes protect the core sample from the circulating drilling water and minimize the loss weathered material and soil filled j9ifit~: A tabular summary of the drilling methods used for each boring is displayed in Table l.All~,OTing logs are located in Appendix B.

Table 1. Summary of drilling methods t' '\ ,-,

, S···

4.25" ID 3" OD 3.160" 3" OD

Boring No. Hollow Split 3.25 ID'~. ODNX Shelby

Stem Spoon Casing-, Rock Tube

Auger Sampler ..,

Core GF-l X X X GF-2 X X X GF-3 X X GF-4 X X GF-5 X X X GF-6 X X GF-7 X X X GF-8 X GF-8A X X X GF-9 X X GF-IO X X GF-11-16 X X X X reI:' 1'1 'V 'V 'lr X'-1.1 -1k A. A A

GF-13 \', X X X X GF-14,

o.

X X X X GF;14a X X GF'~15 X X X GF-17 X X X X GF-18 X X X X GF-19 X X X X GF-20 X X X GF-21 X X X GF-22 X X GF-23 X X GF-24 X X ,

GF-25 X X \

." ~,f

9[~I GannettFleming August 2008

Two undisturbed thin-walled tube samples (i.e., Shelby tubes) were obtained from boring GF-14a in the proposed stilling basin for purpose of determining the engineering properties of the foundation soils. Samples were collected from a depth of 2.0 to 4.0 and 4.5 to 6.5 feet however recovery was not satisfactory due to the presence of coarse grained saturated soils. An additional Shelby tube was obtained from GF-2 at a depth of 20.0 to 22.0 feet and yielded a satisfactory recovery. This sample contained saprolitic soil and was subjected to laborii.~ory testing for classification and compressibility. .

2.2.2 Rock Permeability Testing

Permeability testing was performed in a total of seventeen borings, GF-2 thr,q~b"GF -14 and GF­22 through GF-25. This testing involved the use of pneumatically inflate~'sitl.gle or double packer systems, injection pipe extending from the packers to the sl,lcf~~e"knd"; pump to apply water pressure to the isolated stage within rock. For each te~tiflg's~ge,the water pressure was incrementally increased to a maximum and then decreaseds-usuallyiri five distinct steps where each pressure increment is a complete step. Water pressures~~re computed based on the stage depth, water level within the boring, hole inclination and strat~. thus each testing stage was subjected to a unique series of pressures. Testing sta,g,e"s'W~re generally ten feet in length, with two exceptions being the bottom stages of OF-24 and (W..25 where a single packer was used. Test stages did not overlap except when highly fracttlJ;e rock was encountered, where, in attempts to isolate these zones stage overlap was necessary, Ir{all, 298 test stages were completed during this phase of the subsurface investigation.">

">-"

During this investigation, bo1)J."p{imual and electronic systems were employed to collect rock permeability data. In the manual rhethod. the volume and pressure of water applied to the stage was monitored using a nu\ilting'di'sk water meter (i.e. water service meter) and a dial type mechanical needle pressufe"'gauge (e.g., see Figure 7). Using these tools, timed intervals of several minutes betweeh"Il1~ual observation of the flow meter and pressure gauge, and averaging of flows and pressures between these intervals was used to determine the permeability of the test stage. The manual method was used to test borings GF-4, GF-8, and GF-22.

i~! GannettFleming 10 August 2008

Ragged Mountain Dam - Project No. 48782

Geotechnical Report

Figure 7. Nutating disk water meter and mechanical pressure gauge

Of the 298 stages tests, 62 yielded lugeon values greater than 10 and 25 were classified as open, where an accurate lugeon value eonld not be readily computed. Most of these stages corresponded with highly fractured zones.as recorded on the boring logs. A tabular summary of the permeability data for each boring",!~ lot'ated in Appendix C. Lugeon values are also displayed on the profiles in AppendjxBt.Fjgures B-2 through B-4.

Figure 8. Electronic field instruments and real time display

I~i GannettFleming 11 August 2008

Ragged Mountain Dam -

Geotechnical Report

Project No. 48782

2.2.3 Geophysics

A geophysical survey was conducted at Ragged Mountain Dam during October and November 2007. The survey consisted of using the multispectral analysis of surface waves (MASW) method and seismic refraction. The complete Geophysical Survey Report is in Appendix D. Locations of the MASW and refraction line survey are displayed on Figure D-l within this appendix. !.

2.2.4 Test Pits

The test pit program was completed from January 16-20, 2008ang &psisted of 12 excavations to obtain information about the depth to top of rock, and the irregul~rity of the top of rock surface. All test pits were excavated by L.G. Hetager of Punf'.stltf!wn~'Yr'PA under the supervision of Gannett Fleming, Inc. personnel. Excavation equ~PIJl~nFco~sisted of a John Deere 120C backhoe equipped with a three cubic foot buc~e~, anq ro~k teeth. Test pit data augments information collected during the subsurface invesiiigation"and geologic discontinuity mapping. Multiple photos and a video were taken at each t~st pit location. The classification system developed by Deere and Patton (1971) is utilized to describe the weathering profile as described Table 2. ...

l~j GannettFleming 12 A ugust 2008

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Geotechnical Report

Table 2. Description of a weathering profile for igneous and metamorphic rocks (after Deere and Patton, 1971)

CoreRQD* Relative RelativeZone Description Recovery"

(%) Permeability Stre rigtlf7(%) ,"""",

notI Residual IA-A top soil, roots, organic o medium to :)QW1o Soil Horizon material zone of leaching applicable high , r~edirim

,- l .

and eluviation may be .-,'4 -

porous IB-B not o )ow; '7-' commonly Horizon

characteristically clay­applicable low (high if

accumulations of Fe. Al enriched, also

cemented)

and Si, hence may he cemented

no relict structures present

1C-C relict rock structures oor not low to Horizon retained

glinerally medium O'-fO%applicable medium

(saprol ite) silty grading to sandy (rei ict material structures

veryless than 10% core stones significant)

often micaceous

II Weathered IlA­ variable high (water medium to highly variable, soil-li~e_ ". variable,Rock Transition generally losses low where

(from to rock like ­ generally

0-50 weak residual soi I

10-90% common) structures

or saprolite coarsesand (gruss) . fines commonly fine to

and relict to partly structures are

lOto 95%c~~estonesweathered present rock) , ,~ph~~6clial weathering

'bommon rIB-Partly generally generally medium to medium to Weathered

rock like, soft to hard rock >90% high high**50-75%

joints stained to altered Rcrc!< some alteration of feldspars and micas

III Unweathered no iron stains to trace

Rock along joints >75% generally low to

very high** (generally 100% medium

>90%)no weathering offeldspars and micas

Notes: * The descriptions provide the only reliable means of distinguishing the zones

** Considering only intact rock masses with no adversely oriented geologic structure

I~i Gannett Flerning 13 August 2008

2.2.5 Borehole Video

In two borings, GF-8 and GF-22, the occurrence of questionable material prompted the use of a borehole camera for the purposes of video logging to further evaluate the subsurface conditions. This system consists of a small diameter camera attached to a cable with a winclL~d,

control panel (GeoVISION™, Williamsville, VA). The camera provides a wide angle'\:,lew; directly down the borehole, which can be viewed in the field with a seven-inch LCD ~Qmt6t;and

recorded to either a standard digital video recorder or laptop computer. The intent{9fthis'video investigation technique was to image the borehole sidewalls in an attempt to exp~re\fnd observe the conditions within these questionable zones.

2.3 Laboratory Investigations

2.3.1 Soils Testing Results

The laboratory testing analysis reports are presented in'Xppendix F.

Table 3. Summary of s9il~e§t~llg results -'~""" '~!:f

f".

Moisture Grain, Size Analysis Atterberg Sample Specific Limits Dispersion USCSBoring Location Content ",.

Depth (It) Gravel Sand . -/ Fines Gravity Grade Classification(%)

(%\ .' 1"101 (%\ LL(%) PL(%)

GF-l 4.0 - 4.9 RA 9.9 48.4 29:6 22.0 2.77 29 26 1 GM GF-2 20.0 - 22.0 DC 7.4 3.0 hi 64.3 32.7 N/A NP 8M GF-7 4.5 - 5.8 DC 10.2 18.1 , 62.5 19.4 N/A NP 1 8M GF-7 6.0 - 7.9 DC 9.6\ \31.1 . 53.8 15.1 2.84

GF-8a 22.5 - 23.1 DC . 12.8 0.4 72.4 27.2 N/A NP 1 3M GF-8a 50.0-50.8 DC 23,4 0.0 54.4 45.6 2.87 N/A NP 1 8M

GF-11/16 0.0 - 2.0 LA 27.9 0.1 29.6 70.3 2.85 49 33 1 ML GF·ll/16 4.0 - 5.2 LA '''4.8 0.1 50.5 49.4 2.88 N/A NP 1 8M GF-11/16 21.0 - 23.0 LA 16.9 0.5 57.9 416 2.80 8M

GF-12 4.0 ~ 5.1 .RA -f:-" ",., <~ n 52.5 29.7 NiA NI-' 8MIV.1 I' .0

GF-12 41.6 - 42:0' ;"'"RA 8.9 66.0 25.1 2.73 GF-13 40 - 6.0 / -RA: 11.9 GF-13 10.0-12:0 RA 3.7 3.2 692 27.6 N/A NP 1 8M GF-13 18.0,20.0 .... RA 5.9 13.7 63.2 23.1 N/A NP 1 8M GF-15 4.0 - 5.3', LA 10.9 9.0 50.6 40.4 N/A NP 1 8M GF-17 2.0 -4.0 88 25.8 1.2 53.8 45.0 28 NP 1 8M GF-17 }.6.0 - 8:0 88 5.8 73.9 20.3 GF-18 2:0- 40 RA 59.1 27.9 13.0 GF-19 4.0 - 5.3 RA 7.9 11.9 58.9 29.2 1 Tp-2 DC 6.1 0.0 51.8 48.2 N/A NP 8M Tp-7 4.5 - 5.5 DC 166 0.3 61.4 38.3 N/A NP 1 8M

DC - dam crest LA - left abutment, RA - nght abutment S8 - stilling basin

2.3.2 Rock Testing Results

[~i GannettFleming 14 August 2008

Ragged Mountain Dam - Project No. 48782

Geotechnical Report

Laboratory rock testing was completed by Gannett Fleming Soils Laboratory and Geo Test Unlimited, Inc. (Nevada City, CA). All rock testing was performed on core samples obtained during the subsurface investigation. A summary of testing results is in Table 4.

Slake durability testing was conducted on five samples located at depths at or near the proposed foundation grade for the dam. The purpose of this testing was to determine .the potential for slaking should the foundation grade be exposed for an extended duration prior, to. dam construction. The slake durability index for all samples is greater than 98% signifying that little to no slaking wiII occur during the foundation excavation." z:••

Unconfined compression testing was performed on eleven specimens to,; deterlhine the compressive strength of the bedrock underlying the dam site. The results shliw, tnJlt the granitic gneiss yields an average compressive strength of approximately 19,000 pd~n,d.~~r square inch (psi) with a low of 6,654 psi and a high of 27,858 psi. The specimen'dispt;;lying the lowest strength was from GF-I0 at 27.6 to 28.1 ft and was noted to fail along <;i.'basTc mineral healed diagonal joint. Most of the remaining specimens did not exhibitian'apparent plane of weakness.

;.- -«, :.':'''' ;-;."-,

Direct shear testing was conducted on ten natural jointsand four saw-cut joints. The average angle of internal friction, <p, was determined to b,e47.8 degrees while the saw-cut joints yielded an average of33.0 degrees. The results of.this.testing will be utilized in determining a design <p which will then be used to compute shear~tre~gthofboth discontinuities, intact rock mass and bearing capacity. L '

i~i GannettFlernil1g 15 August 2008

Table 4. Summary of rock testing results

Boring

Sample Top

Depth (ft)

Sample Bottom Depth

(ft)

Rock Type

SI3ke Durability

Index' (%)

Estimated Compressive

Strength' (psi)

Joint Depth

(ft)

Joint Type

Normal,. Loa411

Applie~(Jl$i)

p~~~( friction

,. 3 Angle

.' {rloa\

Density" (pef)

unconfined Compressive

Strength4 (psi)

GF-2 55.0 58.0 0,991 , .s-: " .....

GF-2 59.8 60.6 Granitic Gneiss 60.1 Natural b 40.80; 160 49.5 170.6 27288 GF-2 61.1 63.0 Granitic Gneiss 62.3 Natural, 40, 80, 160 46.1 171.3 11908 GF-3 50.4 51.4 Gneiss 0.991 43100 j 1<·· ••

GF-3 50.4 53.0 Granitic Gneiss 51.9 Natural 40.80,160 32.2 193.2 18773 GF-3 50.4 53.0 Granitic Gneiss 52.5 Natural 40.80, 160 46.3 193.9 17621 GF-6 22.0 Granitic Gneiss 0.989 32948 .~.

GF-6 23,0 25.6 Granitic Gneiss . ",2.3.2""0 ' Saw cut 50. 100,200 36.2 175.7 20000 GF-6 23.0 25.6 Granitic Gneiss !.j.., 2'f,,9c Saw cut 50. 100,200 32.7 GF-6 25.6 27.0 Granitic Gneiss

'" " i 173.8 17584

GF-IO 24.0 27.0 Granitic Gneiss 24.2 Natural 40,80, 160 53.2

GF-IO 24.0 27.0 Granitic Gneiss "" ,. ,. 24.6 Natural 40,80, 160 39.5 177.0 23169 GF-IO 24.0 27.0 Granitic Gneiss : ::':'r'· ' 24.7 Saw cut 40,80. 160 31.0 GF-IO 27.0 28,5 Granitic Gneiss ':'r•••. 177.6 6654

GF-II/l6 38.0 Granitic Gneiss 0.9&3· :ri,. 25468

GF-II/16 41.1 44.1 Granitic Gneiss : ', .. 42.5 Natural 20,40,80 51.0

GF-II/16 41.1 44.1 Granitic Gneiss 175.6 15114

GF-14 25.0 27.0 Granitic Gneiss. ."«'c" 26.5 Natural 20,40,80 45.4

GF-14 25.0 27.0 Granitic Gneiss ..... ' .,. 175.4 22971 GF-15 28.0 30.0 Granitic Gneiss 0.989 32414

GF-15 27.0 29.0 Granitic Gneiss' 27.5 Natural 40,80, 160 54.4 177.4 11711

GF-15 33.7 37.4 Gneiss", 34.0 Natural 40,80, 160 46.1

GF-15 33.7 37.4 Gneiss 34.7 Saw cut 40,80, 160 21.6 171.4 27858

Notes: Obtained from slake durability testing ASTM 04644

Obtained from point load testing ASTM 05731

Obtained from direct shear testing ASTM 05607

Obtained from unconfined compressive testing ASTM D7012

I~i Gannett Fleming 16 August 2008

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Geotechnical Report

2.4 Characterization of Subsurface Conditions

2.4.1 General

Borings GF-I through GF-II-16, GF-12, GF-13, GF-15, GF-18 through GF-21 were completed within the proposed footprint of the dam were completed to evaluate the RCCdall:l

,~_ "",;"'~, __ o,,{

foundation grades, depth to rock and rock permeability. GF-14 and GF-I? were cornpletedto' evaluate the proposed outlet works foundation, depth to rock, and rock permeabipty~"M~re specifically GF-I, GF -12, GF-18 and GF-19, in addition to GF-22 and GF-23 were ,c()fnpfeted to evaluate the proposed east abutment and cut-slope. Borings GF-II-16, GF-24,artdGFi':25 were completed to evaluate the proposed west abutment and cut-slope."

Table 5 summarizes the individual characteristics of all t~ebJ~I1~Jes drilled the subsurface investigation and

Table 6 summarizes the test pits.

2.4.2 Characterization of Soir'€onrlitions',,; ,,',

Soil characterization w~~ bisedon review of published literature, field observations and investigations, laboratory-testing results, and engineering interpretation. In general, the site stratigraphy is defined by re,sidJal soil, saprolite, transition material (saprolite to weathered rock), partly weathered rock. ahd unweathered rock. Descriptions of each unit along with criteria on which these stratigraphic units are based are shown in Table 2.

Based on this criteria and the information obtained from the subsurface investigations, a weathering profile has been developed along the centerline of the proposed dam. The weathering profile is attached in Appendix G.

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Ragged Mountain Dam -

Geotechnical Report

Project No. 48782

Table 5. Characteristics of all borings

12012.0 -o728.9I - -- I' East.Abutment

Boring No. Location Top of Hole Inclination Depth to 24 hr Approximate Total Elevation (degrees) Groundwater Depth to Dep~~

(ft) Level (ft) Bedrock (It) . (ft)',

GF-I West Abutment 695.7 0 N.E. 9.4 "25:0 GF-2 West Abutment 695.0 30 64.5 43.2 »: 248

GF-3 West Abutment 662.3 30 N.R. 33.2.' ,i'" 268 - ,/;;

GF-4 West Abutment 644.6 30 N.R. )7:(}\" 248

GF-5 Valley 583.8 0 Artesian ·;nA.6· .j ,;'···. 218

GF-6 Valley 569.1 30 Artesian 1"""\:; 6:4 ,/' 248

GF-7 Valley 564.2 0 N.R. ( I,:,,>••.,. 9.5 215

GF-8 East Abutment 611.7 30 N;R~''l "': 3.1 248

GF-8A East Abutment 620.0 0 'N.R".1 0.6 51.8

GF-9 East Abutment 655.7 30 55.2:". 24.4 248

GF-IO East Abutment 695.9 30 i'/ ,. 40.7 4.0 248

GF-II-16 East Abutment 706.7 o,e ",\, ,44.1 26.3 165

GF-12 West Abutment 704.8 0 :';' 77.7 16.0 165

GF-13 West Abutment 629.0 0 5.8 21 165

GF-14 Valley 566.7 . I··,:, : 0 3.9 9.8 165 GF-14a Valley 567.2 "0 " N.E. N.E. 6.0C"'. '

GF-15 East Abutment 615.2 I· 0 N.R. 5.6 165

GF-17 Valley 5653 ; 0 1.3 8.4 24.0

GF-18 West Abutment ,701\O:7 0 19.0 4.2 24.0

GF-19 West Abutment -A_ .. '698.7 0 G.R. 4.8 55.2

GF-20 East Abutment : C :\

645.3 0 N.R. 4.3 14.0

GF-21 East Abutment ': 665.6 0 N.R. 1.3 14.0

UF-22 West Abutment 708.9 0 53.1 8.0 100

GF-23 West Abutment 717.4 0 62.2 7.0 120

GF-24 East Abutment 718.2 0 47.9 33.5 120

p,

Gt-L)

N.R. - Not Recorded

G.R. -Grplited within 24 hrs.

N.,E. - Not Encountered

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Geotechnical Report

Table 6. Summary of all test pits

Test Pit No.

Location Approx.

Elevation (ft)

TP-l East Abutment 700

TP-2 East Abutment 675

TP-3 East Abutment 652

TP-4 East Abutment 626

TP-5 Valley 566

TP-6 West Abutment 604

TP-7 West Abutment 631

TP-8 West Abutment 677

TP-9 West Abutment 697

TP-I0 West Abutment 624

TP-l1 Valley 568

TP-12 East Abutment 613

':C,i;;!C';

Reason for Termination

Bucket Refusal

Bucket Refusal

Bucket Refusal

Bucket Refusal " Limits of EquipID~~t '" Limits of'EQ~ibmeht/

Buckef~fusal

Bucket Refti~al ,Bucket Refusal

Limits;f Equipment

"B~cket Refusal

Bucket Refusal

c o,y, o.Termination Groundwater ° AveftlgeDepth JRe(seepage rat!!)

.j'(ft) ,,", .,'

3.5 7N,El'" ..ii?'

10.5 10/N£. 'f,~.F7:6.5 N.R.

;c;;; N:E:f7.0 14

" > 1 gpm 18.5 N.E

19.5 N.E. N.E

12.5 N.E. 13

12.0 N.E. 11 N.E. 95.3

19.0 .'.:, N.EN.E.

N,R.Igpm10.0

7.5 11N.E.

N.E. - Not Encountered

N.R. - Not Recorded

Test Pit depths ranged frPlTI a depth of 3.5 ft at TP-1 located at the east abutment to 19.5 feet at TP-6 located in lhev~,lleY;floor. The test pits indicate that the thickness of residual soil and saprolite varies greatly across the axis of the proposed dam site. The soil thickness ranged from approximately less than one foot to at least 20 ft. The thickness of residual soil and saprolite on the-west abutment is between 10 and 20 ft, with the exception of the area near GF-5 where it is lesstha!1 five feet. Soil thickness on the east abutment is much thinner, with soil thickness lessthanone foot to about five feet. Borings and test pits completed in the valley section also indicate varying soil thickness with depths ranging between 6.4 and 18.5 ft.

All soils were classified in accordance with the Unified Soil Classification System (USCS). Based on the visual and laboratory classification, residual soils at Ragged Mountain Dam consist predominantly of reddish to orangish brown silty sand (SM) with that contain varying amounts of gravel. In some locations, the soil was classified as a silty gravel (GM), but gravel content typically increased with depth. All samples observed were micaceous and moist to dry.

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Geotechnical Report

The underlying saprolite was classified as a brown to grayish brown decomposed granitic gneiss, micaeous, very soft to soft, rippable, friable, and breaks into sand and fine gravel fragments when broken with manual pressure. Saprolitic materials excavated from test pits were dry to moist with the exception of TP-5 and TP-II where groundwater was encountered at depth.

2.4.3 Characterization of Dam Site Bedrock Conditions

Bedrock encountered during the subsurface investigation was classified in'accordance with the ASCE Rock Classification System. A majority of the rock encouqtered in the core borings was classified as medium to coarsely crystalline granitic gneiss';W:ith, quartz veins. Subordinate amounts of fine to medium grained gray to dark gray gneisS'COh,~~irting garnets or metamorphosed mafic rock was also encountered, It is possible thisun~ti,~ younger and intruded the coarsely crystalline granitic gneiss.", -,

Rock cores were generally classified as being hard to very hard and five-foot core runs without fractures were not uncommon, especially at depths gre~fer than 50 ft. Softer rock was encountered in a few locations, either slightly beloWitlle,top of rock or in isolated weathered zones. Similarly, areas yielding low RQD values are,also typically located near the ground surface. By comparison of the core recoverie~\\li!J1d RQDs, pressure testing results and geophysical data appear to be generally cQnsis,tent with each other.

, 2.4;3.1 West Abutment

The top of rock alonglhe west abutment (right, as looking downstream) ranges between 9.4 and 43 ft below ground surface, Rock weathering on the west abutment typically consists of 10 to 30 ft of IIA transition underlain by up to IS ft of partly weathered rock, before transitioning to unweathered.rockat 40 to 50 ft. Zones of partly weathered rock were also discovered beneath unweathered rock; in'(JF-2 through GF-4 and GF-13. Rock cores were generally classified as being hard to ve~yhard, although soft zones were encountered in GF-19, GF-22 and GF-23. The soft zone in:,QF..22, from 34,0 to 44.0 ft was documented by the borehole video camera and a still photO is presented in Figure 9. The rock core recovered from this zone is very soft to moderatelyhard and severely to moderately weathered as most observed joints contained pyrite and had, a sandy texture. From the video logging, the sides of the borehole between 34.0 and 44,0 feet appear to have an unusually rough surface indicative of soft material. Furthermore, the absence of large voids suggests that recovery losses were most likely the result of the rock breaking down into fine cuttings and washing out with the drilling water.

[~i GannettFleming 20 August 2008

Ragged Mountain Dam - Project No. 48782

Geotechnical Report

'.,' ,

'.'". Figure 9. Boring GF-22, soft zone from 34:0 - 44.0 ft

Permeability testing on the west abutmentyieldedZd stages with lugeon values greater than 10, most of which occur near the top of rock:l:Iowever, some stages in GF-2, GF-12 and GF-23 where classified as openly permeable below 7() ft.

2:4.3.2 Valley

"

The top of rock withinthe valley section of the dam is at variable depth. Based on the borings rock is within less thanI;O ft below ground surface, however test pit TP-5 was excavated to a depth of 18.5 feetwithout': encountering rock. The weathering in this section typically consists of IIA transition betWeen 14 and 36.8 ft, underlain by seven to 10ft of IIB partly weathered rock. T\)'o exceptions are GF -5 which transitions directiy into unweathered rock at 36.8 ft below ground surface and GF-7 where the IIB zone extends to 61.5 ft. Unweathered rock is typically located between 19.0 and 33.0 ft. Both GF-5 and GF-6 contained zones of partly weathered\.'l\"..U rock, -<ban':aath\"t thol,", initial u«1 ...weathered1 '"' zone .I.'\...Dock cora", werel'Y\.I again \.11classified as 11VV""Ul l.\:.J l\.f 11 111'V\"t \",. L.V."' • l\,lUl v J \,IU hard1

to very hard and rio substantial soft zones were encountered.

Permeability testing within this section of the dam footprint yielded 13 (out of 62) stages with lugeon values greater than 10, most of which occurred in GF -6. In particular, one stage, GF-6 155.7 to 165.7 ft, was classified as openly permeable.

2.4.3.3 East Abutment

21i~J Gannett Fleming August 2008

The depth of bedrock along the east abutment (left, as looking downstream) ranges from less than 1 foot to 24 ft below ground surface. Weathering in this section typically consists of a five to 25 foot think layer of IIA transition zone rock, underlain by 15 to 45 ft of lIB partly weathered rock. Unweathered rock is typically located between 29 and 60 ft below ground surface. Similar to the west abutment, lIB zones were also located beneath unweathered rock in boring GF-9, GF-10, GF-11/16 and GF-25. Rock cores were typically hard to very hard, although several soft zones were located in GF-8, GF-10 and GF-25.

The soft zone in GF-8 warranted the use of video logging to investigate thertafure of weathering. The first zone of interest is located at approximately 19.6 ft below~r'~tl~~ ;Grface where a two-inch void is noted on the boring log. Video logging indicated ~R5 ff16ng zone what appeared to be micaceous silty sand. Figure 10 contains still photos tal{~ntrom the video logging and a photo of the corresponding core run. Additionally. pressure7~e~ping of this zone yielded a permeability of greater than 100 Lugeons. The surface of thd{djaceh~rockcore has a planer texture and is slightly to moderately weathered. _.

Figure 10. Boring GF-8, approximate depth 19.6 ft

The second questionable zone encountered in this boring is located between 43.0 and 46.5 ft where the driller noted the presence of very soft material, of which no recovery was made. The video logging of GF-8 indicates a 3.9 ft zone of what appeared to be micaceous silty sand. Figure 11 contains four different video captures from within this questionable zone. Boring GF-8A was added to try to encounter this zone of material. GF-8A was drilled vertically

l~i GannettFleming 22 August 2008

up the slope from GF-8 and encountered a highly weathered zone from a depth of 48 feet to 51.8 feet. Samples of the material from 49 feet to 51.8 feet were obtained with a split spoon sampler.

Figure 11. Boring GF~8,~~ghlyweathered zone, approximate depth 42.7 to 46.5 ft

Below a. depth of 53 feet in GF-8, core run recovery and RQD values are 100% and Lugeon values ~d:orded during pressure testing were all less than 1.0. Figure 12 depicts a typical core run takeri'fronr approximately 100 ft below ground surface.

[~i Gannett Fleming 23 August 2008

Ragged Mountain Dam - Project No. 48782

Geotechnical Report

Figure 12. Boring GF-8, typical core extracted fr~i;. depths greater than 50 feet.

The permeability testing in this area cyielded22 (out of 103) stages with lugeon values greater than 10, but 13 of these were crassifi~ as openly permeable where the pump was at maximum capacity and the desired stage pressures were not met. Of the stages that yielded perrneabilities greater than 10 lugeons, ortly 14 are located below 50 ft. Additionally, during the testing of GF-IO from 64.5 to 74.,6, afracture connection was noticed with GF-II/l6 as this boring exhibited artesian flow.'U pO'h completion of the GF -10 test stage, the water level in GF­I 1/ 16 immediately receded.

According to the, boring log for GF-25, the bottom five feet is soft and weathered, prompting the useof a single packer to verify permeability at this depth. The subsequent test yielded a lugeonvalue of less than I from 112.0-120.0 ft.

Base~Lon the boring logs, rock permeability testing, borehole viueo loggings and weathering and geophysical profiles, the proposed foundation grade for the dam has been established between 35 and 55 ft below ground surface, the exact depth of which depends on existing anomalies. In this occurrence. all residual soil and type IIA-transition zone rock would be excavated.

2.4.4 Cut Slopes in Rock

-" ;,..1

i~l GannettFleming 24 August 2008

Ragged Mountain Dam - Project No. 48782

Geotechnical Report

2.4.5 Groundwater Conditions

Groundwater conditions were evaluated based on the water levels recorded during the drilling phase of the subsurface investigation. The readings used in this evaluation are predominantly 24- or 48 hr water levels and therefore, may represent seasonal levels. All available 24-hour readings are presented in Table 4.

Artesian groundwater flow was noted on multiple occasions. Borings GF-6 ,\nd0F.-7 yielded artesian flow for both 0- and 24-hour levels. During rock permeability 4?sti~g:i the artesian flow in these two borings was quantified and converted into a groundwater level. Artesian flow was also encountered during the dri lling of both GF-10, at apPfQ~irriat~ly 114 ft and GF-II/16 at approximately 74 ft. The artesian flow gradually subside<f~,jn"90th instances before drilling was completed. Artesian conditions were not encountered ~l~ewh~re on the east abutment.

2.5 Aggregate Availability

3.0 FOUNDATION GRADE SELECTION

3.1 General

The quality of material chosen asanadeC'{uate foundation for a roller compacted concrete CReC) dam is an important design consid~ratidn. General criteria for the dam foundation are:

(1) The foundatiorf1ev~L milst be located such that adequate bearing capacity IS

provided tos~p:port the structure under various loading conditions. (2) The founillltio~gmde must be located below materials with high deformation

moduli to preVent longitudinal cracking within the structure (3) The, foundation grade must be located below weathered and/or highly fractured

lones fo~ developing adequate shear resistance along the base of the dam, and to provide asuitable surface for successful grouting.

(4) The .foundation grade must be located below fracture zones containing erodible materials that cannot be effectively grouted or that may compress under load.

3.2 Site Geology and Weathering Profile

As previously mentioned, the new Ragged Mountain Dam is located within the Peidmont Physiographic Province. The mapped bedrock unit is the Lovingston Gneiss and can be characterized as a granitic gneiss. A detailed description of this unit is presented in Section 1.3 of this report. Climatic and topographical conditions in the Piedmont promote deep and rapid weathering as the region is humid with significant annual rainfall and mild temperature. The weathering process in this unit typically progresses both downward from the ground surface, but

i~! Gannett Fleming 25 August 2008

Ragged Mountain Dam -

Geotechnical Report

Project No. 48782

can also progress outward from fractures within the bedrock. These fractures serve to conduct acidic surface water to the intact rock. thus accelerating weathering of fracture sidewalls (Sowers 1954. Deere and Patton 1971, Sowers 1994). The portion of the Piedmont within which the site is located is dominated by broad, gently rolling hills and valleys formed by the fluvial erosion of deeply weathered metamorphic and igneous rocks. In the Piedmont, the erosion process is slower than the weathering and therefore, the region is dominated by the occurrence ofthe greatest depth of soils on the ridges and minimal amounts of soil in the valleys (Sowers r?$4~ Sowers 1994). This condition was confirmed during the subsurface investigations perfofIV,~dat the dam site.- ..

The weathering profile in the Piedmont is complicated and often difficult t.0 accurately characterize. Numerous descriptive models have been proposed that are gen~r~Ilysifnilar, but differ somewhat in terminology and division points within the weathering p~ofile.:Three of these descriptive models are illustrated in Figures 19 through 21. Figure 13 is a~.ex'~etpt from Deere and Patton (1971) and represents a visual schematic of the weatheril}gpt9fit~"Jor igneous and metamorphic rocks (see Table 2). Figure 14 and Figure IS are additi6l1fl;ldiagrams respectively depicting Sowers' (1994) and Ruxton and Berry's (1957) models. Further"complications that can occur in the weathering profile are illustrated in Figure 16 which shows the differential depth of weathering that can be expected in the Piedmont due to layering of rock types, intrusive dikes and faults (Sowers 1954). In particular, distinct separation and characterization of materials lying between the residual soil materials at the surfay~and the hard, fresh unweathered rock at depth is problematic. Subsurface explorations are usedtc evaluate the weathering profile, but examination of the figures illustrates how closely-spaced borings could encounter and indicate very different materials, depending on whether the boring happened to be located in predominantly rock material or in highly\veathel;ed areas adjacent to hard rock masses. For this reason, a geophysical survey using multi-channel analysis of surface waves (MASW) was used to obtain data between borings.

The general conditions sl10Wn in the weathering profile illustrations exist at the Ragged Mountain Dam site, withihe;fuJ;!her complication that there are intermixed gneiss and granite­like rocks which behave differently from each other. Borings and test pits clearly indicated that, in some cases, highly or completely weathered zones of the granitic-gneiss underlie the intact rock. In some cases; this occurs at considerable depth in otherwise nearly unweathered rock. In general, an acceptable dam foundation surface would be located within the partly weathered zone shown on Figure n.

!~l 6annett Fleming 26 August 2008

a) Me-,mc Rocks

Zone

I Residual Soil

IIA T.­

Figure 13. Typical weathering profile for metamorphic and intrusive igneous rocks (Deere and Patton'197J)

Figure 14. Weathering profiles in crystalline rock (Sowers 1994)

[Qtji 6annettFlen1ing 27 August 2008

Weathefing ZOntl

thiJ paper.

7".'.' .: ~ -;: " " •-:-:.•••• ' .' • ~ - :EI- .-"':--' .=.....__.. - .- 1 IA 18 .. • " • ... . • ~ .. ~ . • .. ..: ... , .. UV1a~ ...... ....'V'u.".,............. 1 , '.'. 4.' •••••••••••: .", .. f·-.-.-.---~:-.-.-. ---l

.. II ".. .. t .. .. • ~ .. ... " I I -10 ... • ... '" .. .. .. .. ... .. .. .. ..'" ... • lit .. ... .. • . ..' .' .' ..... . . . . . . . . . '. . . . . . . . . . [ Ie . .. .. ... .. ".. ... .. . .. .. -- - - -- ...... -:.: ":'-"_.~ ..:. -_ .. ...:. :- .. ......:. .:. ._---: -:. ~ "-"-': ..:.. :... ...:. ,,~,: -Q' : .,if:{) .' .'d, .. :~/' '.'~~ .. '0'. - - - I

~ '. " .'~. ,' .. ·tV· . .'. , -. 0:' . ' .: '. . , . . .e:» ,." ' '.II

Oi' 'd" (); (0 'e.-0,0 IIA

~_~i.~ ......""'"." r: -4';0.. '. _., :'

-:--:-?~£:f3E[--1=~:~~ .1

liB

111- · _r Ruxton and llerry l19571

F,igut~ 15; Weathering profile of granite " ',' (Deere and Patton 1971)

l~: Gannett Fleming 28 August 2008

Ragged Mountain Dam -

Geotechnical Report

Project No. 48782

" .... .. " RESIDUAL SOIL

.... " ..... " .... ....

....

GROUND SURFACE

Figure 16. Depth of weathering as affected byrock composition, dikes and faults (Sowers 1~~4)

3.3 Design and Construction Foundatiai» Grade Selection

-The design intent is that thefinisheddarn foundation has the following characteristics:

(l) Excavationwill progress to the depth necessary such that the general condition and appearance of'the foundation surface will be hard, fresh rock.

(2) Depth of excavation will be sufficient to ensure that fractures in the foundation surface are either clean, groutable fractures or that the filling in the fractures is non,;erodible.

(3) The foundation surface is expected to be highly irregular due to the characteristics ()f the geology.

The Piedmont is also problematic for both contractors and owners from the standpoint of predicting required grades, excavation quantities, and excavation difficulty. This is particularly true for the lI-lIA Transitional Zone material, which has characteristics of both soil and rock, and which can be erratic in consistency and extent. Construction difficulties are also compounded by highly irregular final excavation grade that often results. Claims and litigation relating to excavation are common, particularly when bidders are inexperienced with geologic conditions.

The difficulties in characterizing conditions, the quality offoundation required, the uncertainty of predictions of required depths of excavations, and the need for fairness to the

l~i GannettFleming 29 August 2008

Ragged Mountain Dam - Project No. 48782

Geotechnical Report

contractor present special challenges in formulating the excavation be specified and performed in stages. (Check with Bob before continuing)

4.0 SEISMIC HAZARD ASSESSMENT

5.0 RESERVOIR RIM SLOPE STABILITY

6.0 REFERENCES

Bowles, 1. E. 1996. Foundation Analysis and Design, 5th ed. McGra~ Hill. ,'- '-\~,;\,.",)

;" ~--,:,:;

College of William & Mary Department of Ge6'1qgy':t"'\7006b. Blue Ridge Province [on-line]. [Accessed 16 July 2006]. Available frorri"1t\¥orld Wide Web: <http://www.wm.edu! geologyIv irginia/prov inces/Blueridge/blue_ridge.html>

/':i~, '

Deere, D.U., and Patton, F.D. 1971. ~lopiStability in Residual Soils. Fourth Panamerican Conference on Soil Mechanics; ond.Foundation Engineering. American Society of Civil Engineering, 87-170. ;' s -o

Fang, H. (ed). 1991. Foundation Engineering Handbook. 2nd ed. Van Nostrand Reinhold.

Fichter, L.S. and Baedke.-Scf. 2000. Structural Cross Section Through the Blue Ridge Province in Central Virginia [online]. [Accessed 19th June 2008]. Available from the World Wide Web: <httpi/jcsmfes.jmu.edu/geollab/vageol/vahist/blurdgdiv.html>

/.jf,,\

Hoek, E., and Bray, J:W. 1981. Rock Slope Engineering 31d ed. Cambridge, UK: University p .• ress ..

Natural Reources Conservation Service. 2007. Web Soil Survey [online]. [Accessedl9th June 2008]. Available from World Wide Web: <http.r/webso ilsurvey.nrcs.usda.govlapp/W ebSoilSurvey.aspx>

Morganstern, 1963

Nelson, W.A. 1962. Geology and Mineral Resources ofAlbemarle County Virginia. 1:9,000. Commonwealth of Virginia Department of Conservation and Economic Development Division of Mineral Resources.

[~I GannettFleming 30 August 2008

Ragged Mountain Dam - Project No. 48782

Geotechnical Report

Sowers, G.F. 1954. Soil properties in the southern piedmont region. Proc. ASCE, 80(416). 4161-4169.

Sowers, G.F. 1994. Residual soil settlement related to the weathering profile. Proceedings oj Settlement 1994, Vertical and Horizontal Deformnations ojFoundation and Embankments. Vol. 2, ASCE. 1689-1702.

U.S. Army Corps of Engineers. 2003. EM 1110-2-1902. Slope Stability.

Virginia Division of Mineral Resources. 1993. Geologic Map oj Virgihia, 1:500,000. Commonwealth of Virginia, Division of Mineral Resources.

!~i GannettFleming 31 August 2008