SHEAR WORK AND PORE WATER PRESSURE IN UNDRAINED SHEAR

When a loose sand is subjected to a cyclic rotation of principal stress axes during an undrained test, excess pore water pressure is generated. To study the nature of pore pressure buildup, several series of laboratory tests were conducted using a hollow cylindrical torsion shear apparatus. Tests were conducted employing different kinds of cyclic loading schemes in which specimens were subjected to cyclic shear stresses with or without continuous rotation of principal stress axes. Based on the test results, accumulated shear work per unit volume was calculated at each stage of shear stress application, and its correlation with the pore water pressure was examined. It was found that, at each state of shear stress alteration, there exists a unique relationship between the shear work and the pore water pressure, independent of the shear-stress history. This observation enables contour lines of equal shear work to be drawn in the stress space. (Author/TRRL)