Investigation into the dynamic stress of pile-supported embankment caused by moving train loads

This study presents a full-scale model of pile-supported embankment with ballasted track-bed. The monitored dynamic stresses enabled the time histories, frequency contents, and distributions to be investigated under different train speeds and axle loads. Results show that the dynamic stress peaks representing the axle effect gradually fell off along depth, in agreement with the filtered frequencies in the Fast Fourier Transform analysis. The great train speeds brought more significant dynamics, slowing down the diffusion of the dynamic stress peaks, while the axle loads rather affect the intensity of dynamic stress. The critical height of dynamic soil arching grew with the increase of train speeds, but the dynamic pile efficacies (the proportion of dynamic load carried by pile) under various train speeds and axle loads were stable at 83.5%. Compared to the ballasted track, the ballastless track showed a dynamic stress dispersing more quickly due to its higher stiffness. Besides, the axle-induced dynamic stress peaks were not visible on the dynamic stress history in the case of ballastless track. Based on the test results and the Boussinesq stress solution, an analytical method was developed to estimate the dynamic stress distribution within pile-supported embankments with good accuracy, taking into account the dynamic stress factors.