PORE PRESSURES AND STRAINS AFTER REPEATED LOADING OF SATURATED CLAY.

Repeated and sustained loading tests on undrained samples of normally consolidated lacustrine clay are used to prove the existence of a relationship between pore water pressures and axial strains. The behavior of the clay is studed by investigating the pore pressure and strain responses under repeated loading, and comparing them with the responses from the more usual sustained loading. Samples under repeated loading fail at a stress below the compressive strength of the material as obtained from a standard strength test. It has been shown that, for a repeated stress level below a critical value a nonfailure equilbrium is reached, closed stress-strain hysteresis loops occur and the soil behavior is essentially elastic. For a repeated stress above the critical value, the effective stress failure envelope is reached and each loading cycle leads to further nonrecoverable deformations and ultimate failure. Experimental proof of the pore pressure versus strain relationship is presented by means of a series of loading tests on normally consolidated lacustrine silty clay samples tested under undrained triaxial conditions.