Abstract: Cluster element in particle flow code (PFC2D) is used to construct numerical specimen in light of the large internal friction angle and brittleness at post-peak stage of tested sandstone. A set of micro-parameters that can reproduce the macromechanical behavior of sandstone were calibrated through comparing with the experimental results under triaxial compression. Then two different radial unloading paths are simulated. The numerically simulated results show that the peak strength increases with the increasing of initial axial stress, and has a similar trend with the experimental results. The evolution characteristic of microcrack numbers under two radial unloading paths is analyzed. The damage extent under radial unloading is more serious than that under axial loading. Furthermore, the ability to withstand damage enhance with the increasing of initial axial stress. From the analysis of displacement field under different loading paths, it is clear that sandstone fails due to the discontinuity of displacement.

Key words: radial unloading, simulation by particle flow, cluster cell, microcrack, displacement field