Experimental study on deformation behaviors of overconsolidated clay under cyclic confining pressure

Traffic loading is usually simulated by single cyclic deviator stress. However, the vertical normal stress and horizontal stress acting on the soil elements are all varied cyclically under traffic loading. Nevertheless, part of the subgrade soil is overconsolidated, rather than normally-consolidated. There are few researches on the development of the accumulated axial strain of the overconsolidated soft clay under traffic loading. Recognizing this, a series of cyclic triaxial tests with cyclic confining pressures are conducted on overconsolidated clay under undrained conditions, and the effects of the cyclic confining pressures and overconsolidated ratios on the development of accumulated axial strain are investigated. It is observed that the relationship between the accumulated axial strain and the number of cycles are similar under different test conditions, in which the accumulated axial strain increases rapidly at the beginning of tests and increases with a decreasing rate to achieve a stable value. Besides that, the overconsolidated ratios and cyclic confining pressures have a significant effect on the development of the accumulated axial strain: both the cyclic confining pressure and the overconsolidation ratio inhibit the development of the accumulated axial strain. By comparing with the accumulated axial strain obtained under cyclic triaxial tests with the constant confining pressure, the accumulated axial strain decreases by 7.7% and 15.8% when the slopes of stress path are 1.0 and 1.5, respectively. Additionally, the accumulated axial strain ratio of the overconsolidated soft clay and normal consolidated clay decreases from 0.122 to 0.040 as the overconsolidated ratios increases from 1 to 8. The above research results may deepen the understanding of the deformation evolution of the overconsolidated soil under traffic loading, and provide experimental basis for the establishment of prediction formula for the deformation of the overconsolidated soil under traffic loading.