Regional/areal reconnaissance and investigation of candidate areas/sites
The importance of regional/areal geoscience investigations for data critical to selecting candidate areas/sites for engineering works and for related supplies of natural materials is frequently overlooked. Project sponsors have commonly restricted the efforts of the exploration team to only the area near an initially selected candidate site, and sometimes this attitude persists during the planning and design phases (discussed in Chapters 19 and 20, this volume). This limited approach disregards the potential importance of much relevant geological information, because sites rarely conform to a preconceived interpretation. In many cases, an understanding of neotectonic conditions, geomorphic history, and active regional geologic processes can prove more advantageous to an engineering objective than restricted, detailed knowledge of a single site (Fig. 1). A very early example of this occurred during a reconnaissance for the proposed Roundout Valley tunnel alignment for New York Board of Water Supply in 1906. C. P. Berkey recalled (Sanborn, 1950, p. 46), “consultant W. O. Crosby left the party and drove far beyond the line of tunnel; on his return Crosby understood the geology of the site better than anyone could from a mere inspection of the alignment, and it was a good practical lesson in reconnaissance technique.”
Several examples of how an inadequate understanding of areal geology subsequently affected project design are given in case histories cited herein and in Chapters 19, 20, and 23, this volume. Moreover, regional/areal geological investigations have been utilized with increasing effectiveness as one basis for the most economic and effective approach to selecting suitable locations for engineering works (Fig. 1).
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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.