Cyclic Stress-Strain Characteristics of Clay

Abstract

The decreases in moduli and increases in yield strain occurring during cyclic loading of sensitive clay under simple shear conditions are examined. The loading conditions are representative of those associated with the upward propagation of a seismic shear wave through a large mass of soil; i.e., the strain is completely reversed during each cycle at the rate of 1 cps. The moduli and yield strain reported are those defining the bilinear hysteresis models which best fit the nonlinear stress-strain characteristics obtained from the tests. For San Francisco Bay Mud the moduli are constant for strain levels greater than 2% and for loading cycles after the fiftieth. Yield strain, however, is proportional to cyclic strain level for at least 200 cycles. The strength and moduli measured under static loading conditions are decreased by cyclic loading involving large strains, but only the modulus is decreased by loading restricted to strains below about 1%.