Strain localization characteristics of liquefied sands in undrained cyclic torsional shear tests

In this paper, results of undrained torsional shear tests on Toyoura sand, Urayasu boiled sand and Christchurch boiled sand specimens were examined to evaluate and clarify the combined effects of key factors (i.e. density, mean effective stress, cyclic and static shear stresses) on the limiting value of shear strain at which strain localization (i.e. shear band formation) appears in liquefied sandy soils. All tests were conducted on fully-saturated medium-size hollow cylindrical specimens (H = 300 mm, D-out = 150 mm and D-in = 90 mm), which were prepared by air-pluviation method, thus producing a sand fabric with horizontal bedding planes. A state-of-the-art torsional shear apparatus was used to achieve a single amplitude shear strain level of 50%. Non-uniform specimen deformation was clearly observed in all tests and shear strain level to initiate strain localization could be methodically determined from test results based on the change in deviator stress properties during cyclic loading.