Variation characteristics analysis of sandstone strength parameters in discrete element method by using internal scale ratio

The mesostructural characteristics of sandstone determine its macro-engineering characteristics. To better understand the relationship between cohesion of sandstone particles and strength in the present study, the FISH programming language was used to design a particle flow test program and conduct uniaxial compression tests of geomaterials. Twelve numerical specimens with diameters of 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0?mm were designed for uniaxial compression tests. A total of 41 tests were carried out to simulate three bond strengths between particles with no friction and 19 internal friction angles from 0° to 90° under weak and strong bonding conditions. According to the failure modes and stress–strain curves of the specimens, the influence of the inner scale ratio on the particle flow was analyzed. The following particular phenomena were observed: (1) With the increase in the bond strength between particles, it was more difficult for the particles to rupture, and the number of micro-cracks was drastically reduced. (2) When the bond strength remained constant, the failure modes before and after the internal friction angle of 45° were completely different, which was related to the shear failure angle. (3) The curve dropped significantly after the strong bonding peak, and the brittle failure characteristics were evident. (4) The changes in the strength parameters between particles did not change the energy transfer mode, and the change of the bond strength increased the proportion of the strain energy in the input energy. (5) In the case of weak bonding, the proportion of the strain energy in the input energy gradually decreased with the increase in the internal friction angle. When the bond was strong, the proportion of the strain energy was stable, with an insignificant decrease as the internal friction angle increased.