A Quantitative Study of Micro and Macro Mechanical Parameters Based on the PFC(3D) Flat-Joint Model

The flat-joint model, which constructs round particles as polygons, can suppress rotation after breakage between particles and simulate more larger compression and tension ratios than the linear parallel-bond model. The flat-joint contact model was chosen for this study to calibrate the rock for 3D experiments. In the unit experiments, the triaxial unit was loaded with flexible boundaries, and the influence of each microscopic parameter on the significance magnitude of the macroscopic parameters (modulus of elasticity E, Poisson’s ratio ν, uniaxial compressive strength UCS, crack initiation strength σ(ci), internal friction angle φ and uniaxial tensile strength TS) was analysed by ANOVA (Analysis of Variance) in an orthogonal experimental design. Among them, E(ƒ), k(ƒ) has a significant effect on E; C(ƒ) and k(ƒ) have a significant effect on ν; C(ƒ), σ(ƒ) and k(ƒ) have a significant effect on UCS; C(ƒ); σ(ƒ) and E(ƒ) have a significant effect on TS; R(sd) has a significant effect on σ(ci); and φ(f), E(ƒ), k(ƒ), μ(ƒ), and σ(ƒ) have a significant effect on φ. Regressions were then carried out to establish the equations for calculating the macroscopic parameters of the rock material so that the three-dimensional microscopic parameters of the PFC can be quantitatively analysed and calculated. The correctness of the establishment of the macroscopic equations was verified by comparing the numerical and damage patterns of uniaxial compression, Brazilian splitting, and triaxial experiments with those of numerical simulation units in the chamber.