Cyclic Loading of Silty Clay with Drainage Periods

Undrained repeated load triaxial tests are carried out on anisotropically (K_o) normally consolidated specimens of a silty clay. Each specimen is subjected to five periods of loading at 0.1 Hz. The loading periods have a maximum duration of approximately 2,000 cycles, and are separated by drainage periods. A variety of cyclic loading magnitudes are applied. The experiments show that large permanent shear strains and pore pressures develop during the first few loading periods, particularly during the application of high cyclic deviator stress amplitudes, leading to failure. This is defined as an accumulated shear strain of 0.6% during a particular loading period. Drainage periods have a significant strengthening effect, even though the changes in water content are small, and it is observed that during the later loading periods very little permanent strain or pore pressure development occurs. The number of drainage periods required to produce this condition increases as the magnitude of the cyclic loading amplitude increases.