Mechanism of Pore Pressure Increase of Saturated Granular Materials Subjected to Repeated Loads

Abstract

A series of undrained torsional shear tests were conducted to investigate the variation of excess pore water pressure of saturated sand during undrained cyclic loadings. The test results indicate that there is a threshold of cyclic stress ratio for specimen to reach liquefaction. Above the threshold, the excess pore water pressure gradually increases during undrained cyclic loading and is eventually equal to the initial effective confining stress. The double amplitude of shear strain also increases gradually, showing a weakening development of the shear strength of the specimen. Beneath the threshold, the excess pore water pressure stops increasing eventually regardless of how many cycles are applied. Moreover, the excess pore water pressure rises sharply just after the reverse of the loading direction, which suggests that an evident tendency of negative dilatancy is accordingly induced. The excess pore water pressure cannot always increase with the shear stress, and it decreases when approaching the phase transformation line. Based on introducing a variable that is defined as the increment of the excess pore water pressure during a unit variation of the shear strain, the tendency of volume change of the specimen can be well represented.KeywordsUndrained testsRepeated loadingSaturated sandExcess pore water pressureShear deformation