Investigation of preferred sites for selection and design
Preferred sites represent those locations that have been identified and subsequently survived a Phase I screening against a set of general locational, design, and environmental requirements, which provide the basic ingredients for functionality. Ordinarily, the candidate sites are identified on a broad basis, using small-scale topographic maps (less than 1:250,000 scale), remote images such as aerial photographs, and aerial reconnaissance; geologic factors are partly downgraded, due to the lack of specific details provided during this second phase of feasibility investigations (Chapter 18, Fig. 1).
Preferred sites, representing Phase II of a project, are those considered worthwhile on the general basis of location and topography, design requirements, environmental impact potential, seismic and groundwater characteristics. By their nature, Phase II efforts are geologically intensive. During Phase II investigations, reconnaissance-level mapping and subsurface exploration, sampling, and testing of the materials can provide enormous returns when planned and conducted by mature and field-experienced applied geologists.
The concept of the alternative site-selection process emerged in the 1930s, as a result of developments in the internal combustion engine, which served as a power plant to drive mass-produced heavy construction equipment. Thus, early, large-scale heavy construction projects, such as dams, canals, and tunnels, were possible. With this capacity, national governments and cities alike became owners of transportation and water supply projects that could have, by nature of their function, several choices for location.
Heavy construction was widespread during the 1930s, with projects like dams of the Tennessee Valley Authority, and Boulder (Hoover), Coulee, and Shasta dams, and dozens of military bases and installations for World War II.
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A review of milestones and changes in geological theory and practice from which modern engineering geology in North America has developed. Five chapters discuss historical events and the contributions of early scientists and engineers; nine chapters review the state of knowledge of dominant geologic processes, phenomena, and specialized principles critical to modern practice; and three chapters discuss geologic environs and the properties of construction materials. Four chapters are devoted to geoscience investigations and related techniques for: initial regional-areal evaluation of conceptual candidate sites (Phase I); selection of preferred-designated sites and design (Phase II); typical kinds of investigations used during project construction (Phase III); and as-built documentation and explorations of the operating or rehabilitation phases. Closing chapters focus on the geoscientist's responsibilities relative to engineering failures, errors of judgment that impact works, litigation, and forensic geoscience. The 34 contributors present extensive case histories applicable worldwide.