LIQUEFACTION OF SATURATED SAND IN TRIAXIAL TORSION SHEAR TEST

ABSTRACT Strain-controlled cyclic torsion tests were run on a saturated sand using a triaxial torsion apparatus in which the vertical piston was designed so that its cross sectional area was equal to that of the specimen. In the first series of tests, a cyclic twist was applied while keeping the principal stress ratio constant. In these tests liquefaction did not occur and failure was associated with the development of a large amount of shear strain. In the second series of tests, a sample was consolidated anisotropically and then subjected to a cyclic twist while preventing entry of the cell water. This produced the situation in which the lateral expansion of the sample was completely confined. In these tests liquefaction did occur and the sample consolidated anisotropically was found to develop pore pressure faster than the sample consolidated isotropically. Such difference in the potentiality of pore pressure development was accounted for by the fact that the lateral stress was gradually increased during cyclic loading until the principal stress ratio became equal to unity at the onset of liquefaction. The concept of the principal stress ratio change during cyclic loading was used to account for the difference in liquefaction potential between the normal type of a cyclic triaxial test and a simple shear test.