The deformation characteristics of a kaolin clay under intermittent cyclic loadings

Metro train loading or machine vibration is characterized by intermittent cyclic loading interspersed with resting periods between loading cycles. The deformation of soft clay subjected to such unique cyclic loading may be different from that under consecutive cyclic loading, as reconsolidation occurs during the resting or drainage period. A series of cyclic triaxial tests were performed on a kaolin clay under both intermittent and consecutive cyclic loading patterns. The effects of including drainage periods between loading cycles on the deformation characteristic of the clay are investigated under different cyclic stress amplitudes, resting periods, consolidation confining pressures and over consolidation ratios. The results indicate that including drainage periods between loading cycles improves the cyclic resistance of the clay during subsequent loading cycles. However, compared with those under continuous cyclic loading, the overall axial strain and excess pore water pressure accumulation are much greater under the intermittent loading patterns, and the shorter the duration of resting period, the greater the overall accumulation. This means that including reconsolidation between loading cycles would enlarge the final deformation of soft clay. For the normally consolidated samples, the strain accumulation after reconsolidation highly depends on that developed in the first cyclic loading stage. Excess pore water pressure accumulated during each cyclic loading stage is negligible at given cyclic stress in over consolidated clay, whilst the axial strain accumulates notably in the first cyclic loading stage, but marginally after that. This may be attributed to the attenuation adjustment of microstructure in soil as cyclic loading continues.