GEOTECHNICAL ENGINEERING AT THE SAVANNAH RIVER SITE AND BECHTEL

The authors describe two aspects of geotechnical engineering; site characterization utilizing the CPT and recognition of aging as a factor affecting soil properties. These methods were pioneered by Professor Schmertmann and are practiced by the Bechtel Corporation in general and at the Savannah River Site in South Carolina, in particular. This paper describes a general subsurface exploration approach that we have developed over the years. It consists of ''phasing'' the investigation, employing the principles of the observational method suggested by Peck (1969) and others. In doing so, 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 shallow subsurface soils are of Eocene and Miocene age. It was recognized that the age of these deposits would have a marked effect on their cyclic resistance. 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 plays a major role in the cyclic resistance of the soils at the SRS, and that aging should be accounted for in liquefaction potential assessments for soils older than Holocene age

Soil Amplification at Treasure Island During the Loma Prieta Earthquake

The Loma Prieta Earthquake ground motions recorded on Treasure Island, a man-made fill in San Francisco Bay were considerably greater than on the adjacent Yerba Buena rock outcrop. The Yerba Buena motions were used as input to the computer program SHAKE90 for computing soil amplification at Treasure Island. Shear wave propagation velocities were obtained by seismic cone penetration testing. Reasonable agreement was observed between the computed and recorded accelerations at the strong motion recording station. The maximum computed accelerations around the island ranged from 0.13 to 0.20 g\u27s. The degree of damage at various locations on the island correlated somewhat with the maximum computed accelerations