2016 Volume 4 Issue 2 Pages 17-22
This paper reports on the influence of initial static shear on large deformation behavior of very loose (Dr = 24-30%) Toyoura sand subjected to undrained cyclic loading. A series of isotropically consolidated torsional simple shear tests were carried out on hollow cylindrical specimens up to single amplitude shear strain exceeding 50%. Two types of cyclic loading patterns, namely reversal stress and non-reversal stress, were employed by varying the magnitude of combined initial static shear and cyclic shear stresses. The observed types of failure were distinguished as liquefaction and residual deformation based on the difference in the effective stress paths and the modes of development of cyclic residual shear strain. Test results revealed that, similar to the case of medium-dense Toyoura sand (Dr = 44-50%) previously investigated by the Authors, under reversal stress loading, failure could be associated with liquefaction followed by extremely large deformation during cyclic mobility. Contrarily, under non-reversal stress loading, a progressive accumulation of residual (plastic) deformation brought specimens to failure although liquefaction did not occur. Moreover, the presence of initial static shear does not always lead to a decrease in the liquefaction resistance or strain accumulation of very loose sand. In fact, its resistance can increase or decrease with an increase in initial static shear stress, but it strongly depends on the combination of static and cyclic shear stresses and, thus, on the type of loading. However, under the same magnitude of combined shear stresses applied, very loose sand is much weaker against large cyclic shear strain accumulation than the medium-dense sand.
