1 1-05-1997 1 1 : 53At1 FROI-1 SUBTERRA I NC 206 889 8150
<br />
<br />
<br />
<br />1997 Annual Meeting Abstracts
<br />(Alphabetical According to Lead Author)
<br />(coat'd)
<br />MIIQE SUBSIDENCE AND ROCKFALL HAZARDS:
<br />A CASE STUDY FROM NORTHWEST COLORADO
<br />Chris L. Breeds
<br />(cmt'd)
<br />eau from this event, and olds, natural clili farluros, was
<br />used W develop input data that were used in the Rocldall
<br />Hazards evalwtiaa
<br />As a resuh of the ctndy, appm>®ately 3,000 fact of 20•
<br />foot deep trench was constructed behvern Cotmry Road
<br />27 and the Twentymile cliff to intercept and contain
<br />boulders. Ia addition, a 1,500.foot section of the eotmty
<br />road eves relented towaMa the cottm ro enable
<br />construction of the remedial messmea. A short section of
<br />the cli9' subsequently Sited during ;,.~.:crwu,,,,y ,...
<br />approximately twenty boulders, weighing bdwarn 10 and
<br />900 tons were stopped by the trtmch
<br />This papa describes the site investigation, rockfaB
<br />6autdc analysis, selection and design of remedul
<br />measures, and evaluates the performmce of the selected
<br />schemes.
<br />FOUNDATION EVALIIATION OF EXLSTING
<br />CONCRETE DAMS -GEOLOGIC AND
<br />ENGiNEERQ~iG CONSIDERATIONS
<br />Michael N. Brucn, Hare Enginsering Conrparry, ?33
<br />Somh WackerDrlve, Cln'cago, IL
<br />Stability evalvatiws of existing concrete dams requiter a
<br />lborough uoderstaadmg of the dam fotmdatioa m order m
<br />users the performance and safety of the sttvctrues. With
<br />the aging of dams, many of which are over 50 years old,
<br />dam owners are facing signifitmt rehabilitation vests to
<br />upgredc structures to meet strmggtt criteria for dam
<br />stability.
<br />In the evaltatioa of dam stability. the analysis of concrete
<br />structures is extremely sensitive m 6urtdation paramaers
<br />and uplift assumptions. -the importance of geologic and
<br />foundation conditions to the selection of appropriate
<br />foundation shear strength parameters and uplift
<br />asstmtptioas cannot be ova emphasiDed. The key
<br />geologic fetters influencing the sliding stability of the
<br />concrete structure era lithology, vRaUrering, and
<br />geometric un5guration and smfice charadetistics of the
<br />discontinuities. Several key design and construction
<br />factors with regard to the dam formdation are also
<br />considered, including foundation preparation and
<br />rrcamr®t. surface profile, and the depth of rock
<br />excavation. in the malysis of sliding fiilure of concrete
<br />gravity structures on rock, the Critical plane(s) of
<br />we~lmess are the coouerdrock intedace md/or adverse
<br />geologic features in me Iotmdatioa.
<br />la the assesnaeot of cmerae strudtes, the protest
<br />mchdes a review of all existing project information,
<br />geologic and gootahniul investiption and testing
<br />reports, crosVUdion documents, in particular
<br />correapmdmce, dawiags and photogtapha, previous dam
<br />safety impectieo reports, and inttrumeoution data; and
<br />review of published laboratory fast data for similar rock
<br />type. Following the review process. additional
<br />exploration, Lborstary testing, and inmumeataGoa dau
<br />will often be required in order to reduce geologic
<br />tmcertaintiesvr the stability evaluation. The tendency to
<br />be overly conservative m the cubiGty evahmlion by using
<br />high fittors of safely noel low shear strength sad high
<br />uplift assumptions em be avoided by uamg sound geologic
<br />and mginoaittg judgment.
<br />SAN FRANCISCO OAKLAND BAY BRIDGE -
<br />c,,,a,. utxvetr unnrrawa.a,friant -w
<br />PI!'RSPECI'IVE FROM FOUNDATION
<br />INVESCIGATIONS
<br />Reid L. Buefl, Jamey Cheri, and Thong La, State of
<br />California, Departrnenr ojTronsportaNon, Engrnerring
<br />Servlcr Center, OJJIce of Srrucrurof Fovndarlons,
<br />Snvcturc Forndatiom Branch, 5900 Fol.~am Blvd.,
<br />Sacramento, G1
<br />The Califomia Department of Transportation (Caltrans) is
<br />currently inwlved with the retrofit andlor reptacemrnt of
<br />the Sea Francisco Oaklend Bay Bridge - Fps[. This
<br />impotent bridge rtms 6om Oakland to Yaba Buena
<br />Island in the middle of San Francisco Bay. Caltrans has
<br />investigated subsurface conditions of the existing bridge
<br />for seismic retroft design putposos. Water depths
<br />beneath the bridge range 6om approximately 5 to 95 feet.
<br />Frencisem Formation bedrock is exposed at Yerba Buena
<br />Island oa the west ben slopes esstwud to dgoWs of
<br />approximately 400 feU below sea level. Above the
<br />Ftanciscen bedrock Gas the Pleistocate Alameda
<br />Fottnatioa, Yaba Buena Mud, McrritVPocry/San
<br />Antonio Formation, and Holotrne Yormg Bay Mud
<br />Subsurface daL was acquired by a drilling and sampling
<br />program condutted by Cahrans which included geologic
<br />logging, dowaholc geophysical long (including P-S
<br />wave logging), and laboraWry testing. Foundation design
<br />and amlyses consisted of developing site spet~t.grauna
<br />motions, evalmting existing foundation npacities, sad
<br />developing foundation rewmmendations for the rerofit
<br />fotmdationa. The majority of the existing foundations
<br />coasiA of Douglas Fa timber piles. The westemmos[
<br />four formdatioas ace large niccons. Proposed retrofit
<br />desilp for the limbo pile formdatians consisted of driving
<br />fivefoot diameter steel pipe piles wound the perimeter of
<br />the exirting limbs pile foundations. Cturent direction of
<br />the project a for rcplaccmmt of the San Francisco
<br />Oakland Bay Bridge -East. Ghraas has yet®tly
<br />completed a bathymetric survCy of the bay extending
<br />2000 feet north and 1000 feet somh of the existing
<br />AEG'97 88
<br />P. 3
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