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<br />. <br /> <br />~~ <br /> <br />.. <br /> <br />. <br /> <br />... <br /> <br />. <br /> <br />EM 1110-2-1913 <br />31 Mar 78 <br /> <br /> <br />Table 2-2. 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 shown foundations to be stable and presenting no under- <br />seepage problems. <br /> <br />Use standard levee section developed through experience. <br /> <br />2. Preliminary geological investigation: Required for all cases except those <br />in 1 above. Use to decide the need for and scope of subsurface explora- <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 testing and more detailed geologic study: <br />a. Preliminary phase: <br /> <br />(1 ) <br />(2) <br />(3) <br />(4) <br /> <br />Widely but not necessarily uniformly spaced disturbed sample <br />borings (may include split-spoon penetration tests). <br />Test pits excavated by backhoes, dozers, or farm tractors. <br />Geophysical surveys (seismic or electrical resistivity) to <br />interpolate between widely spaced borings. <br />Borehole geophysical tests. <br /> <br />b. Final phase: <br /> <br />(1) Additional disturbed sample 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 />borrow areas. <br /> <br />2-3 <br />