Errors of geologic judgment and the impact on engineering works
Many of the more common causes of physical failures or serious remedial problems of engineering works are related to the construction or operation and maintenance phases of a project and involve either controversies or errors of geologic judgment. Mistakes and misunderstandings that impact on a project, including an incorrect design, may be due to any of several causes, such as a misinterpretation of available geological facts, inadequate factual background data, or misunderstanding, misjudgment, or poor forecasting of the geolpgic changes that occur with time and/or operation. Frequently the errors of judgment committed are related to the cost/benefit and/or calculated-risk evaluations of a project, as discussed later in this chapter.
Many faulty interpretations of areal and site-specific geologic conditions have been traced to a lack of input by mature, field-experienced geologists. Even more frequently the errors are a function of insufficient funds for adequate investigations. Management is often under pressure to expedite the investigative stage of the project; in a few instances, site assessment has been attempted by inexperienced individuals or non-geologists, as in the case of the St. Francis dam failure (Chapter 22, this volume). On rare occasions, accusations have claimed incompetence or intentional misinterpretation of the geologic environs for self-serving purposes. However, the authors are unaware of any such instance of fraudulent practice by a professional geologist.
Judgment plays a particularly important role in the planning stage of most major engineering works; for example, in comparing alternative sites for structures or determining routes for aqueducts or highways. Errors of judgment during planning may lead to design problems or result in a failure to achieve the maximum potential benefits from the project.
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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.