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Attempts to sample a saturated gravel deposit beneath a proposed nuclear power plant with standard drilling methods and sampling techniques were unsuccessful. To provide the necessary information on in-situ stratigraphy and density, an alternate exploratory method and sampling technique was designed. In this method, a 107-cm (42-in.) uncased shaft was drilled to a depth of 14.3 m (47 ft) after freezing the soil around the shaft location. The soil stratigraphy, composition, and structure in the uncased shaft were then exposed in great detail for mapping and photographing. Two frozen undisturbed samples were cut from the walls of the shaft in loose gravel layer and the in-situ density was determined using a fluid displacement technique. Maximum and minimum densities were obtained for the thawed soil for calculation of in-situ relative density. Standard Penetration Test (ASTM D 1586, Penetration Test and Split-Barrel Sampling of Soils) results successfully indicated the approximate location and thickness of the loose layer despite the sampling difficulties and high gravel content. Judging from inch-by-inch blow count data, the high gravel content increased the penetration resistance values (through the spoon pushing a large gravel piece) in only a small number of samples.
Assistant professor of civil engineering, Clarkson College of Technology, Potsdam, N.Y.
Lead engineering geologist, Stone and Webster Engineering Corp., Boston, Mass.
Stock #: GTJ10445J