BEHAVIOR OF CLAYEY SANDS UNDER UNDRAINED CYCLIC TRIAXIAL LOADING

The response of two clayey sands to undrained cyclic triaxial loading is described. Both the stress history and the cyclic stress level have been varied. The behaviour is compared with that observed for the clayey sands tested under monotonic loading. Effective stress paths for the normally consolidated soils loaded monotonically in triaxial compression and extension are shown to form a bounding envelope which determines the pattern of behaviour under cyclic loading. A threshold strain is identified, below which cyclic straining results in stable behaviour. Above the threshold strain, pore pressures and strains accumulate under cyclic loading at a rate that increases as the effective stress state approaches the bounding envelope. On reaching the bounding envelope in triaxial compression, the clayey sands strain-soften. On reaching the bounding envelope in triaxial extension, there is liquefaction.