Influences of Cyclic Confining Pressure on Deformation Behaviors of Soft Clay under Intermittent Cyclic Loading

Both cyclic loading on soil and intermittent periods come into play with the passing of trains. However, the existence of both cyclic deviator stress and cyclic confining pressure has already been observed in the stress field. In this paper, two types of cyclic triaxial tests, i.e., continuous cyclic loading and intermittent cyclic loading, were conducted to study the deformation behaviors of soft clay. The effects of cyclic confining pressure, duration of intermittent period (i.e., intermittent time), and loading cycles were analyzed. Compared to continuous cyclic loading, the intermittent period has a substantial influence on the deformation behavior of soft clay: the strain produced by intermittent cyclic loading is larger than that produced under undrained conditions, but less than that generated under partially drained conditions. The increment of accumulated axial strain corresponding to each loading stage under various factors was compared: an increase in intermittent time and loading cycles leads to greater degradation of the increment of accumulated axial strain, while the greater cyclic confining pressure corresponds to lower the increment of accumulated axial strain. The differences in the increment of accumulated axial strain for various loading cycles and cyclic confining pressures are significant in the cyclic loading period of the first loading stage, and can be ignored in subsequent cyclic loading periods. Besides, an empirical formula is provided to calculate the total accumulated axial strain caused by intermittent cyclic loading, and the predicted results accord well with the measured data.