A strength prediction model of soil-rock mixture with varying rock proportions

Soil-rock mixtures in fault fracture zones are composed of rock blocks with high strength and fault mud with low strength. In this paper, in order to study the mechanical properties of the soil-rock mixture with non-cohesive matrix, a large-scale laboratory triaxial compression test with a specimen size of 500 mm×1000 mm is conducted, combined with numerical simulation analyses based on the two-dimensional particle flow software PFC2D. The macroscopic mechanical response and mesoscopic fracture mechanism of soil-rock mixtures with varying rock block proportions, block orientation angles and matrix strengths are studied. The results indicate the following: (1) When the proportion is less than 30%, the shear characteristics of the mixture are similar to those of its non-cohesive matrix. When the proportion is in the range of 30-70%, the internal friction angle and cohesion increase rapidly, and the softening characteristics of the mixture become more apparent. When the proportion exceeds 70%, the aforementioned effect slows. (2) The strength of the mixture is positively correlated with its matrix strength, and the influence of the matrix strength on the loading curve of the mixture is related to the block proportion. (3) When the block orientation angle is 0°, the cohesion and internal friction angle are slightly greater than those at an angle of 90°. Based on the above, for the soil-rock mixture with non-cohesive matrix, a strength prediction model based on the block proportion is given when the block orientation angle and matrix strength are consistent.