Discussion on Failure Mechanism and Strength Criterion of Sandstone Based on Particle Discrete Element Method

In order to study the mechanism of loading failure process of deep rock mass, particle flow numerical simulation (PFC2D) was used to carry out rock mechanical unit tests under different loading strain rates for sandstone in Haitangshan Tunnel, Fuxin. The applicability of several classical strength criteria was compared according to the test. The results show that, except Poisson’s ratio, the other mechanical parameters are positively correlated with the loading strain rate, including peak strength, elastic modulus, cohesion, internal friction angle and tensile strength. And the Poisson’s ratio is negatively correlated with the loading strain rate. And the crack initiation stress σci and dilatation stress σcd increased gradually, but the effects on σci/σpk, σcd/σpk and σci/σcd were not obvious; and at the same volume strain, the corresponding axial strain decreased gradually. The anisotropy of normal and tangential contact forces between particles increases with the increase of loading strain rate. The normal contact force was approximately symmetrical distributed up and down, while the tangential contact force was approximately symmetrical distributed in the center. The cumulative number of cracks and the number of cracks every 10 steps gradually increased with the loading strain rate, and the crack development and failure degree gradually increased, and the crack hot spot map at the shear fracture zone gradually tended to be irregular. By comparing different strength criteria, it was found that the error of ROCKER strength criterion was relatively small, and the calculation was simple. It was considered that ROCKER strength criterion was more suitable for sandstone strength prediction under different loading strain rates.