Published: Jan 1971
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Large (260-mm) diameter samples are required to provide relevant laboratory consolidation and strength data on clay soils which exhibit a fabric of layers, varves, silt, and organic inclusions or fissures. Large clay specimens with permeable fabric can show coefficients of consolidation 103 to 104 times those measured on conventional small samples. The undrained strength of fissured clays decreases with increase in specimen size and improved representation of fabric.
Examination of initial small (76-mm) diameter continuous samples allows a selection of location, quality, and size of representative samples relevant to the geology and the engineering problems. Photographs of visual fabric are compared with laboratory data and field performance to illustrate when large samples are essential.
Use of a 260-mm thin-walled flush-tube piston sampler with 6 percent area ratio gives good quality samples. Handling and extraction of organic clays under water is necessary to prevent oxidation of rootlet channels. Laboratory test equipment is illustrated.
sampling, clay soils, fabric, consolidation, strength evaluation, tests
Professor of soil mechanics, Simon Engineering Laboratories, University of Manchester, Manchester,