Post-cyclic mechanical behaviors of laterite clay with different cyclic confining pressures and degrees of reconsolidation

Abstract

The post-cyclic mechanical behaviors of subgrade soil are usually assessed by conventional cyclic triaxial tests, however, the stress field induced by traffic loads consist of not only a cyclic deviator stress, but cyclic confining pressure and shear stress. Meanwhile, the pore water is allowed to be discharged under traffic loads. Furthermore, the traffic load-induced excess pore water pressure can be partially dissipated after load-cycling. Thus, different reconsolidation processes should be considered. Recognising this, cyclic loading with variable confining pressure was applied to remoulded laterite soils under partially drained conditions, and reconsolidation was allowed. The development of effective stress paths, excess pore water pressure, and undrained strength of post-cyclic shear process were analysed. Results show that the development of effective stress paths is similar and all stress paths cross the critical state line. Besides which, the remoulded laterite clay always has a positive excess pore water pressure and tend to dilate. The undrained strength will be increased under different conditions such that the greater the cyclic confining pressure, cyclic deviator stress, number of cycles, and degree of reconsolidation, the larger post-cyclic undrained strength. Moreover, the post-cyclic undrained strengths between cyclic loading with and without cyclic confining pressure were compared: the undrained strength ratio of cyclic confining pressure to that under constant confining pressure increases linearly with increasing slope of the stress path. Nevertheless, the post-cyclic undrained strength after reconsolidation can be obtained by the corresponding undrained strength without reconsolidation: the ratios of post-cyclic shear strength with and without reconsolidation increase with increasing degree of reconsolidation. At a certain slope of stress path, the undrained strength increases linearly with degree of reconsolidation.