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