Effect of Cyclic Loads on Undrained Strength of Two Marine Clays

Specimens were first isotropically consolidated, then subjected to stress-controlled cyclic loading, and finally monotonically loaded to failure. Tests were conducted on normally consolidated specimens and overconsolidated specimens with an overconsolidation ratio of 4. Comparisons with the results of standard undrained triaxial compression tests indicate that cyclic loading prior to undrained shear causes a small reduction in undrained shear strength and a significant reduction in undrained modulus. Excess pore-water pressures generated by cyclic loading were also found to correlate well with the double amplitude strain induced by cyclic loading. A reduction in effective stress is associated with the excess pore pressures. The decrease in effective stress is largely responsible for the reduction in undrained shear strength after cyclic loading.