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<br />11"
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<br />EM 1110-2-1913
<br />31 Mar 78
<br />
<br />CHAPTER 2
<br />
<br />FIELD INVESTIGATIONS
<br />
<br />2-1, Preliminary and Final Sta~es, Many field investigations are con-
<br />ducted in two stages: a preliminary stage and a final (design) stage,
<br />Normally, a field investigation in the preliminary stage is not exten-
<br />sive since its purpose is simply to provide general information for
<br />project feasibility studies. It will usually consist of a general
<br />geological reconnaissance with only limited subsurface exploration and
<br />simple soil tests, In the design stage, more comprehensive exploration
<br />is usually necessary, with more extensive geological reconnaissance,
<br />borings, test pits, and possibly geophysical studies, The extent of
<br />the field investigation depends on several factors, Table 2-1 lists
<br />these factors together with conditions requiring extensive field inves-
<br />tigations and design studies, Sometimes field tests such as vane shear
<br />tests, groundwater observations, and field pumping tests are necessary,
<br />Table 2-2 summarizes, in general, the broad features of geologic and
<br />subsurface investigations.
<br />
<br />Section I. Geological Study
<br />
<br />2-2. Scope, A geological study usually consists of an office review of
<br />all available geological information on the area of interest, and an
<br />on-site (field) survey, As most levees are located in alluvial flood-
<br />plains, the distribution and engineering characteristics of alluvial
<br />deposits in the vicinity of proposed levees must be evaluated, The
<br />general distribution, nature, and types of floodplain deposits are
<br />directly related to changes in the river and its tributaries. Each
<br />local area in the floodplain bears traces of river action, and the
<br />alluvial deposits there may vary widely from those in adjacenc areas,
<br />The general nature and distribution of sediments can be determined
<br />through a study of the pattern of local river changes as a basis for
<br />selection of boring locations.
<br />
<br />2-3. Office Stu~v, The office study begins with a search of available
<br />information, such as topographic, soil, and geological maps and aerial
<br />photographs, Pertinent information on existing construction in the area
<br />should be obtained, This includes design, construction, and performance
<br />data on utilities, highways, railroads, and hydraulic structures, Avail-
<br />able boring logs should be secured. Federal, state, councy, and local
<br />agencies and private organizations should be contacted for information.
<br />
<br />2-4, Field Survey. The field survey is commenced after becoming
<br />familiar with the area through the office study, Walking the proposed
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<br />2-1
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