Accumulated permanent axial strain of a subgrade fill under cyclic high-speed railway loading

The ballastless track system (BTS) is widely adopted in the construction of high-speed railways (HSRs), in which the vehicle-induced cyclic stresses are evenly transferred to subgrade at a smaller amplitude compared with the conventional ballast track system. In this study, both static and cyclic triaxial tests were performed on a subgrade fill procured from a HSR construction site in Mainland China. The subgrade fill contained high fine content (d < 0.075 mm). The stress-strain-strength relationship from static tests provided a reference for the cyclic tests. The permanent axial strain and resilient modulus under cyclic HSR loading were studied based on the stress levels in the field. Based on the test data, a new empirical equation is proposed to predict the accumulated permanent axial strain with cycle number and low cyclic deviator stress. A new method for determining all parameters in this equation is proposed and verified by fitting test data. The results show that the predictions from the newly proposed relationship are in good agreement with the experimental results. The resilient behavior of the fill under cyclic loading is also investigated. It is found that under low-stress levels the resilient modulus slightly decreases with the increase of stresses, which is not well described by existing models.