Experimental and Numerical Study on Triaxial Failure Mechanism of Rock–Concrete Combined Body

The triaxial mechanical properties of rock–concrete combined bodies are crucial for the safe operation of concrete engineering on rock foundations. Hence, this study uses a combination of mechanical experiments, theoretical analysis, and numerical simulations to investigate the triaxial responses of different rock–concrete combined bodies under different confining pressures. The results indicate that the order of the triaxial strength and deformation resistance of rock–concrete combined bodies is G-C50, S-C50, G-C30, and S-C30, from large to small, due to the effect of the low-strength materials. With the increase of confining pressure, the peak deviatoric stress of the rock–concrete combined body increases exponentially, whereas the axial ultimate strain, radial ultimate strain, and elastic modulus, which characterize the deformation resistance of the combined body, all show a linear increasing trend, and the sensitivity of the combined body to the confining pressure is becoming stronger. For combined bodies with the same bedrock and different concrete grades, the increase in cohesion exceeds 20%, whereas for combined bodies with different bedrock and the same concrete grade, the increase in the cohesion is less than 11%. Moreover, the internal friction angle of the combined body also exhibits a similar variation pattern. Based on the experimental analysis results, a triaxial DEM model for rock–concrete combined bodies considering real aggregates is established, and the effectiveness of the model in predicting the triaxial mechanical properties of rock–concrete combined bodies is verified, which has important theoretical significance and application value.