(Received 30 September 1999; accepted 31 October 2002)
Published Online: 2003
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The influence of stress history and stress state during consolidation and shearing were studied experimentally under undrained triaxial compression and extension modes, by using the Recompression and SHANSEP techniques. In the SHANSEP tests, the samples were consolidated to a vertical consolidation stress of about 1.5 to 2 times of the preconsolidation pressure under Ko consolidation condition, followed by swelling to required overconsolidation ratio before subjecting to undrained shear. Whereas in the Recompression technique, the samples were directly consolidation to in situ effective stress before undrained shearing, the volumetric strains of the reconsolidation were less than 2%, indicating relatively reasonable sampling quality. From the undrained shear results, the Recompression tests give higher undrained shear strength than estimated from SHANSEP tests by about 28%, indicating that some destructuring of soil structure may have occurred in the SHANSEP tests due to large vertical deformation during consolidation. Consequently, the undrained shear strength and the undrained modulus obtained from the SHANSEP tests were much lower.
Geotechnical Engineer, MAA Geotechnics Company, Ltd., Bangkok,
Asian Institute of Technology, Bangkok,
Stock #: GTJ11260J