Strain Increment and Stress Directions in Torsion Shear Tests

Abstract

The directions of the major principal strain increment, stress, and stress increment during rotation of the principal stress axes at any stress level are studied for \IK\N\do-consolidated clay using a torsion shear apparatus with individual control of the vertical normal stress, the confining pressure, and the shear stress on hollow cylinder specimens under undrained and drained conditions. The torsion shear tests are performed along predetermined stress-paths, which are chosen to cover the full range of rotation of principal stress axes from 0° to 90° relative to vertical. The test results indicate that the major principal strain increment directions coincide with the major principal stress directions at failure. The directions of major principal strain increment coincide with the directions of major principal stress increment at low stress levels and with the directions of major principal stress at higher stress levels. This indicates that the behavior of clay gradually changes from elastic to plastic as the stress level is increased. Elasto-plastic theory is therefore suitable for modeling the behavior of clay during rotation of principal stress axes.