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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 <br />