Recompression of Normally Consolidated Clay After Cyclic Loading

Abstract

ABSTRACT Cyclic loading may cause settlements in addition to the settlements due to static loads. 'This paper presents a study of recompression settlements occurring in normally consolidated clay when pore pressure generated by undrained cyclic loading dissipates. The study was based on 18 stress-controlled cyclic direct simple shear tests and 6 conventional consolidation tests on normally consolidated Drammen clay. The specimens were subjected to either one or several series of undrained cyclic loading and drainage. Afterwards, most of the specimens were consolidated further to a vertical stress three times the effective stress at start of cycling. The study showed that undrained cyclic loading and drainage makes normally consolidated clay more resistant to later undrained cyclic loading. The recompression index was influenced by cyclic loading, and for normally consolidated Drammen clay the settlements occurring when the cyclically induced pore pressure dissipates, may be calculated by a recompression index which is 1.5 times the recompression index from a conventional consolidation test. The compression index of specimens which where subjected to undrained cyclic loading and then consolidated past the initial consolidation stresses decreases with increasing cyclically induced pore pressure and increasing cyclic shear strain at the end of cycling.