Deformation Characteristics of Sands under Cyclic Loading

A knowledge of the dynamic stress-strain characteristics of sand subjected to controlled values of shear strain commonly encountered in the field during strong ground shaking is often desirable. Cyclic load simple shear tests have been used to investigate soil performance at shear strain amplitudes greater than those possible from many other types of dynamic laboratory testing equipment. It was found that dynamic modulus values determined near the upper limit of shear strain amplitude that might be expected to be induced by seismic shaking (0.1%) were as much as 40% lower than modulus values obtained at the lowest values of shear strain that were investigated (0.01%). Modulus values were also found to increase slightly with increasing numbers of cycles and with increasing relative density. Values of hysteretic damping, determined from hysteresis loops, showed damping to increase with increasing shear strain amplitude and to decrease slightly with increasing numbers of cycles and increasing values of vertical stress. Curves summarizing the effects of the several parameters on dynamic soil properties have been presented.