Site Characterization Philosophy and Liquefaction Evaluation of Aged Sands — A Savannah River Site and Bechtel Perspective

Abstract

The authors describe two aspects of geotechnical engineering; site characterization utilizing the CPT and recognition of aging as a factor affecting soil properties. These were pioneered by Professor Schmertmann and are practiced by the Bechtel Corporation in general and at the Savannah River Site in South Carolina. This paper describes a general subsurface exploration approach that we have developed. It consists of "phasing" the investigation, employing the principles of the observational method suggested by Peck (1969) and others. We have found that the recommendations proposed by Sowers in terms of borehole spacing and exploration cost are reasonable for developing an investigation program, recognizing that through continuous review the final investigation program will evolve. At the SRS a field investigation and laboratory testing program was devised to measure and account for aging as it relates to the cyclic resistance of the site soils. Recently, a panel of experts (Youd et al., 2001) has made recommendations regarding the liquefaction assessment of soils. This paper will address some of those recommendations in the context of re-assessing the liquefaction resistance of the soils at the SRS. It will be shown that, indeed, aging should be accounted for in liquefaction potential assessments for soils older than Holocene age.