Study on shear behavior and microstructure of rock and cemented paste backfill interface

The shear performance of the rock-CPB interface is the basis for in-depth understanding of the arch effect of CPB. In this study, the rock-CPB sample was prepared for direct shear test to study the influence of different mix proportion, curing time and JRC on rock-CPB interface properties, and the microstructure was analyzed. The results show that the presence of saw-tooth structure accelerates the increase rate of shear stress. Due to the large strength difference between the rock structure and the CPB structure, the failure mainly occurs at the interface between the two structures and in the CPB structure, and no obvious deformation and failure phenomenon is observed in the rock structure. The shear failure envelope of the rock-CPB composite samples follows the Mohr-Coulomb failure criterion. The adhesion of the rock-CPB interface increases with the increase of solid content, c/t ratio, curing time and JRC, and the friction angle of the rock-CPB interface increases with the increase of solid content, c/t ratio and curing time. H-1 NMR test results showed that with the increase of solid content, c/t ratio and curing time of CPB, the proportion of macropores and secondary pores in CPB decreased, while the proportion of micropores pores increased. There is obviously excessive porosity near the rock-CPB interface, and the porosity decreases gradually with the increase of the distance from the interface.