STUDY ON THE MECHANICAL PROPERTIES AND FAILURE BEHAVIOR OF HORIZONTAL SOFT-HARD INTERBEDDED ROCKS CONSIDERING SIZE EFFECTS

Soft-hard interbedded rocks are widely distributed in China, and previous research on their mechanical properties and failure behavior rarely considered the influence of size effects. Taking horizontal soft-hard interbedded rocks as examples, this paper used the finite-discrete element method (FDEM) to study the mechanical properties and failure behavior of soft-hard interbedded rock samples with different aspect ratios, layer thicknesses and layer thickness ratios. The results indicate that: The compressive strength of the soft-hard interbedded rocks decreases and tends to stabilize with the increase of the sample aspect ratio δ. For case I samples with a width w consistently larger than twice the layer thickness t, when δ≥1.0, the compressive strength tends to stabilize, and both the hard and soft layers of the sample fail. For case II samples with continuously decreasing width, when w<2t, the strength of the sample stabilizes at the strength of the soft layer itself, and only the soft layer of the sample fails; The simulation results with different widths and thicknesses further validate the critical value characteristics of w=2t, i.e., the strength and failure characteristics of the soft-hard interbedded rock samples are both critical at w=2t; The simulation results with different layer thickness ratios λ indicate that as λ increases, i.e., the proportion of hard layer increases, the strength of the sample increases and stabilizes at λ≥3.0, but it is still smaller than the compressive strength of the hard layer itself, indicating that the weak interlayer has a decisive impact on the overall mechanical properties of the sample.