Pore pressure characteristics of sand subjected to irregular loadings

A series of undrained cyclic triaxial tests are conducted under various types of artificial irregular loadings to investigate the combined effect of loading amplitude and sequence on the pore pressure characteristics of saturated loose sand. The results indicate that the earlier the higher-amplitude stress pulses arrive in a time history, the larger the pore pressure generation and thus the lower liquefaction resistance the sand samples display. The stress pulses prior to or after the arrival of the maximum spike stress play different role in the development of the pore pressure. In addition, a fairly unique relationship exists between the accumulated pore pressures and the normalized loading cycles. In view of this, the concept of shear work per unit volume is introduced to investigate the evolutionary trend of the excess pore water pressure generation during irregular loadings. The relationship between the pore pressure ratio and the normalized shear work is barely affected by the amplitude and the sequence of stress pulses in the irregular loadings, but shown to be dependent on the type of sand.