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<br />. <br /> <br />) <br /> <br />. <br /> <br />. <br /> <br />" <br />1 <br /> <br />El>l 1110-2-1913 <br />31 Mar 78 <br /> <br />Table 2-2. <br /> <br />Stages of Field Investigations <br /> <br />1. Investigation or analysis produced by rapid field reconnaissance and discus- <br />sion with knowledgeable people is adequate for design where: <br /> <br />a. Levees are 10 ft or less in height. <br />b. Experience has shoYn foundations to be stable and presenting no under- <br />seepage problems. <br /> <br />Use standard levee section developed through experience. <br /> <br />2. <br /> <br />Required for all cases except those <br />for and scope of subsurface explora- <br /> <br />Preliminary ~eolo~ical investiRation: <br />in 1 above. Use to decide the need <br />tion and field testing: <br /> <br />a. Office study: Collection and study of <br /> <br />(1) Topographic~ soil, and geological maps. <br />(2) Aerial photographs, <br />(3) Boring logs and well data, <br />(4) Information on existing engineering projects. <br /> <br />b. Field survey: Observations and geology of area, documented by <br />written notes and photographs, including such features as: <br /> <br />(1) Riverbank slopes, rock outcrops, earth and rock cuts or fills. <br />(2) Surface materials. <br />(3) Poorly drained areas, <br />(4) Evidence of instability of foundations and slopes. <br />(5) Emerging seepage, <br />(6) Natural and man-made physiographic features, <br /> <br />3. Subsurface exploration and field testin~ and more detailed ~eologic studv: <br />a. ~elioina~v uhase: <br /> <br />(1) <br />(2) <br />(3) <br />(4 ) <br /> <br />Widely but not necessarily uniformly spaced disturbed saople <br />borings (~ay include split-spoon penetration tests). <br />Tes~ pits excavated by backhoes, dozers, or fa.~ tractors. <br />Geop~vsical surveys (seis~ic or electrical resistivity) to <br />interpolate be~ween videly spaced borings. <br />Borehole geophysical tests. <br /> <br />b. Final phase: <br /> <br />(1) Additional disturbed s~~ple borings, <br />(2) Undisturbed sample borings. <br />(3) Field vane shear tests for special purposes. <br />(4) Field pumping tests (primarily in vicinity of structures). <br />(5) Water table observations (USing piezometers) in foundations and <br />borro'ioo' areas. <br /> <br />.' . <br /> <br />2-3 <br /> <br />~, ~' : : : I ..' . <br />