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<br />. <br /> <br />Chapter 3 <br />Geotechnical Investigation <br /> <br />'. <br /> <br />3-1. Planning the Investigation <br /> <br />a. Purpose. The pmpose of Ihe geolechnical inves- <br />tigation for wall design is ID identify !he Iype and distri- <br />bution of foundation malerials, ID identify soun:es and <br />characleristics of backfill maleria1s, and ID delennine <br />maleria1 pammelers for use in design/analyses. Specifi- <br />cally, Ihe information obIained will be used 10 selecllhe <br />Iype and deplh of wall, design Ihe sheet pile wall sys- <br />Iem. estimale earth pressures, 10caIe Ihe ground-WaIer <br />level, estimale seltlemenls, and identify possible cOn- <br />slruction problems. For flood walls, foundation under- <br />seepage conditions musl also be assessed. Detailed <br />information regarding subsurface exploration Iechniques <br />may be found in EM 1110.1-1804 and <br />EM 1110-2-1907. <br /> <br />. <br /> <br />b. Review of existing information. The fUS! s1ep in <br />an investigational program is ID review existing daIa so <br />IhaI !he program can be tailored 10 confinn and exlend <br />!he existing knowledge of subsurface conditions. <br />EM 111 0-1-1804 provides a detailed listing of possible <br />dala sources: importanl sources include aerial phOIO- <br />graphs, geologic maps. surficial soil maps, and logs <br />from previous borings. In Ihe case of floodwalls, S1udy <br />of old IopOgraphic maps can provide infonnalion on <br />past riverbank or shore geomelry and identify likely fill <br />areas. <br /> <br />c. Coordination. 'I'hC geolechnical investigation <br />program should be laid oul by a geolechnical engineer <br />familiar wilh !he projecl and !he design of sheet pile <br />walls. The exploration program should be coordinaled <br />with an engineering geologisl and/lI' geologist familiar <br />with the geology of !he area. <br /> <br />3-2. Subsurface Exploration and She' <br />Characterization <br /> <br />. <br /> <br />a. Reco1l1lilissance phose and feasibility phose <br />uploration: Where possible, exploration programs <br />should be accomplished in phases so !hat infonnation <br />obtained in each phase may be used advanlageously in <br />planning later phases. The resu11s of each phase are <br />used 10 "characlerize" Ihe sile deposils fll' analysis and <br />design by developing i"-!;7M maleria1 profiles and <br />assigning material properties. For long, 1inear sttuclures <br />like f100dwalls, geophysical methods such as seismic <br />and resistivity techniques often provide an ability 10 <br /> <br />EM 1110-2-2504 <br />31 Mar 94 <br /> <br />rapidly defme general conditions aI mOOc:st COSL In <br />alluvial flood plains, aerial photograph slUdi~ can often <br />locale recenl channel ftlling or olher poIential problem <br />areas, A modera!e number of borings should be <br />obtained aI Ihe same time 10 refme Ihe sile characleriza. <br />lion and 10 "ca1ibrale" geophysical fmdings. Borings <br />should exlend deep enough 10 sample any malerials <br />which may affecl wall perfonnance: a deplh of five <br />times Ihe exposed wall heighl below Ihe ground surface <br />can be considered a minimum "rule of Ihumb." For <br />floodwalls a1Dp a levee, !he exploration program must <br />be sufflCienl nOl only 10 evalU8le and design Ihe sheel <br />pile wall syslem bul also assess !be slability of Ihe ov~. <br />all levee system. FlI' Ooodwalls where underseepage IS <br />of concern, a sufflCienl number of Ihe borings should <br />exlend deep enough 10 eslablish Ihe lhickness of any <br />pervious strala. The spacing of borings depends on Ihe <br />geology of Ihe area and may vary ~ sile ~ ~ile. <br />Boring spacing should be selecled 10 mtersecl distincl <br />geological characleristics of Ihe projecL <br /> <br />b. Preconstruction engineering and design phase. <br />During lhis phase, explorations are conducled 10 develop <br />detailed materia1 profiles and quantification of malerial <br />pammelers. The number of borings should Iypically be <br />two 10 five times Ihe number of preliminary borings. <br />No exacl spacing is recommended, as the boring layoul <br />should be conttoUed by Ihe geologic conditions and Ihe <br />characleristics of Ihe proposed structure. 'Based on Ihe <br />preliminary silechaJacterization, borings . should ~ <br />silUaled 10 confum Ihe location of significant changes 1R <br />subsurface conditions as weU as 10 confum Ihe continu- <br />ity of apparendy consislenl subsurface conditions. AI <br />this time, undislurbed samples should' be obtained flI' <br />1aboraIory IeSling and/or in silo !ests should be <br />peifonned. <br /> <br />c. Construction general phase. In some cases, addi- <br />tional exploration phases may be useful 10 resolve ques- <br />lions arising .1Iuring detailed design 10 provide more <br />detailed information 10 bidders in Ihe plans and specifi. <br />cations, subsequent 10 conslrUCtion, or 10 support claims <br />and modifications. . <br /> <br />3-3. Testing of Foundation Materials <br /> <br />a. General, Procedures for lesting soils are <br />described in EM ll1B-2-19O!!. Procedures for lesting <br />rock specimens are described in Ihe Rock Testing <br />Handbook (U.s. Anny Engineer Waletways Experimenl <br />Stalion (WES) 1980), Much of !he discussion on use of <br />\aboralory tests in EM ll1B-1-1804 and EM 1110-2- <br />1913 also applies 10 sheel pile wall design. <br /> <br />3-1 <br />