Abstract: Undrained and drained monotonic as well as undrained cyclic torsional shear loading tests are carried out on saturated Nanjing sand at various relative densities in a hollow cylinder apparatus. The test results indicate that the phase transformation line appears to be independent of drainage conditions, but is lower when relative density is denser under monotonic torsional shear loading. In the cyclic torsional shear loading tests under undrained condition, as to the loose specimen, the excess pore pressure and the torsional strain increase rapidly when the stress path approaches the phase transformation line defined under monotonic torsional shear loading with identical initial conditions, which lead to specimen in instable state. Subsequently, initial liquefaction occurs. For the dense specimen, it shows cyclic mobility when the stress path approaches the phase transformation line defined under monotonic torsional shear loading with identical initial conditions. With the loading going on, the stress path presents a series of papilionaceous overlapped hysteresis loops with the border of failure line. At the moment, the excess pore pressure fluctuates around a nearly constant value and cumulative pore pressure no longer increases. The phase transformation line defined under cyclic loading appears to coincide with the phase transformation line defined under monotonic loading, which seems independent of the relative density.

Key words: monotonic torsional shear, cyclic torsional shear, saturated sand, liquefaction