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Unformatted text preview: EM 1110-1-1804 1 Jan 01 3-1 Chapter 3 Regional Geologic and Site Reconnaissance Investigations 3-1. Background Regional geologic and site reconnaissance investigations are made to develop the project regional geology and to scope early site investigations. The steps involved and the data needed to evaluate the regional geology of a site are provided in Figure 2-1. The initial phase of a geologic and site reconnaissance investigation is to collect existing geologic background data through coordination and cooperation from private, Federal, State, and local agencies. Geologic information collected should then be thoroughly reviewed and analyzed to determine its validity and identify deficiencies. Geologic data should also be analyzed to determine additional data requirements critical to long-term studies at specific sites, such as ground water and seismicity, that will require advance planning and early action. Upon completion of the initial phase, a geologic field reconnaissance should be conducted to examine important geologic features and potential problem areas identified during collection of background data. Field observations are used to supplement background data and identify the need to collect additional data. a. Geologic model. Geologic background and field data that are determined to be valid should be used to construct a geologic model for each site. The model, which will require revisions as additional information is obtained, should indicate possible locations and types of geologic features that would control the selection of project features. Preliminary geologic, seismic, hydrologic, and economic studies should be used to indicate the most favorable sites before preliminary subsurface investigations are started. Proper coordination and timing of these studies, and incorporation into a GIS, can minimize costs and maximize confidence in the results. b. Small projects. Many civil works projects are too small to afford a complete field reconnaissance study as outlined below. For smaller projects, emphasis should be placed on compilation and analysis of existing data, remote sensing imagery, and subsurface information derived from on-site drilling and construction excavations. A geologist or geotechnical engineer should be available to record critical geotechnical information that comes to light during investigations. An extensive photographic and video record taken by personnel with some background in geology or geotechnical engineering can serve as a reasonable proxy for onsite investigations. Section I Coordination and Information Collection 3-2. Interagency Coordination and Cooperation Sources of background information available from other organizations can have a substantial influence on project economy, safety, and feasibility. During initial investigations, project geologists may be unfamiliar with both the regional and local geology. Limited funds must be allocated to many diverse areas of study (e.g., economics, real estate, environment, hydrology, and geology). areas of study (e....
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