(Received 14 November 2007; accepted 27 May 2009)
Published Online: 2009
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In this study, constant-water-content direct-tensile-shear (DTS) tests were performed on specimens of kaolinite clay using a new apparatus. Existing studies on strength of clayey soils consider soils subjected to tensile stress, compression-shear stress, or triaxial stress, but only few of them account for combinations of tension and shear. The clay specimens used in this study had an average water content of 15 %. At this water content, the clay is unsaturated, the pore water distribution corresponds to the complete-pendular state, and the soil is subjected to an equivalent effective stress of 400 kPa when external confinement stress is not applied. Each specimen in the DTS test is subjected to an initial tensile stress that is maintained constant while the shear stress is gradually increased until the specimen fails. The results from DTS tests combined with other constant-water-content triaxial compression tests in the same clay produced a failure envelope defined by tensile as well as frictional components. It was found that the Mohr circles derived from the DTS tests are tangent at a common point; this point represents the tensile strength of the material. In other words, the direct shear stress applied produced a tensile failure. These concepts are helpful for understanding and analyzing the behavior of unsaturated soils and other materials subjected to tensile-shear state of stresses, which may lead to formation and/or propagation of cracks. Examples of soils subjected to tensile-shear state of stresses are slopes and desiccating soils and landfill covers.
Vesga, Luis F.
Professional Engineer, Director of Geoscience Division, Domeight Research Institute, Pittsburgh, PA
Stock #: GTJ101563