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Probabilistic Methods in Geotechnical Engineering Appendix A: Background and Statement of Work BACKGROUND The issues of safety and reliability are of great importance in geotechnical engineering. Beginning in the 1970s, a number of researchers began to examine how probability and reliability methods could be used to characterize geotechnical uncertainties. Although some practical applications of probability and reliability theory have been made, after twenty years of such effort most areas of geotechnical engineering have not been influenced to any perceptible degree, and many geotechnical engineers remain skeptical of the value of reliability theory as applied to geotechnical engineering problems. Reasons for this lack of widespread application may include the following: The quality of data available on a typical geotechnical project is too meager for effective use of traditional statistical methods. In addition, variation in site conditions makes it difficult to combine statistical data from different sites. In the process of applying probabilistic methods to geotechnical engineering, the problems tend to be oversimplified, thus the results achieved do not reflect the real issues at the specific site. Most engineers are not well versed in probability language and analysis and may be reluctant to substitute what they perceive to be unverified theory for good engineering judgment. Early applications of probabilistic and reliability methods may have been improper, producing vague or inconsistent results and thus driving engineers away from further applications. Despite these issues, proponents of probabilistic and reliability methods point out benefits for use in geotechnical applications, including: providing a relative measure of reliability levels between alternative designs to facilitate design decisions;
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Probabilistic Methods in Geotechnical Engineering assuring consistent reliability levels between modes of performances, so that resources may be optimally used through a balanced design; comparing contributions from individual sources of uncertainty and their relative impact on the reliability of geotechnical performances, thus setting guidelines for a cost-effective site exploration, testing, and instrumentation program and for allocation of further information and future research efforts; and assisting the refinement of engineers' judgment based on site data and observed performances, such that the benefits of judgmental information and observed data may be properly recognized and integrated. STATEMENT OF WORK A committee, under the auspices of the Geotechnical Board, will convene a two-day workshop of 20 to 25 skilled geotechnical professionals to be held in the spring of 1992 in Washington, D.C. Prior to the workshop, the committee will meet to plan the workshop; primarily consideration will be given to identifying and developing a case example or examples of the successful application of reliability methods in a geotechnical project. The workshop will consist of an equal number of probabilists and traditionalists invited to engage in the following activities: Present and discuss successful and unsuccessful case examples of the use of probabilistic and reliability methods in geotechnical engineering practice. Foreign applications, especially in France and Japan, will be examined. Deliberate on reasons for the slow acceptance of probabilistic and reliability methods. Develop position statements regarding the potential value and the current useability of such methods in geotechnical engineering practice. Define important research and technology transfer needs for application of probabilistic and reliability methods in geotechnical engineering practice. Identify areas where these methods are most likely to contribute to geotechnical practice. A set of questions will be developed beforehand to focus on a variety of issues regarding the use of reliability methods in geotechnical engineering. Each participant will come to the workshop prepared with answers to those questions and ready for further discussions. The workshop will form the centerpiece of the study. A workshop is the proper activity for the study because of the need for diverse expert opinion, information exchange, and identification and debate of issues. The workshop itself will not yield definitive conclusions and recommendations; a report, to be completed after the workshop, will summarize the workshop findings and reach conclusions and recommendations. A
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Probabilistic Methods in Geotechnical Engineering preliminary assessment undertaken by the Geotechnical Board indicates that the board contains the necessary geotechnical expertise on reliability methodologies and is balanced between probabilists and traditionalists. However, a workshop committee (consisting of selected board members and possibly others) will be appointed through standard NRC committee appointment procedures. This committee will be subject to NRC bias procedures. The committee will meet to plan the workshop and to prepare a report after the workshop.
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