Investigation of the Shear Mechanism at the Interface Between Grout and Brittle Rock: Physical Testing and PFC3D Simulation

Abstract

Experimental tests were conducted in the laboratory to investigate the shear behavior of interfaces in grout-gypsum specimens. Various specimens were created to produce different interface configurations for testing and modeling. The tensile strength measurements indicated that grout has a strength of 1.2 MPa, while gypsum measures 0.52 MPa. For Young's modulus, grout was found to be 9 GPa, in contrast to gypsum's 4 GPa. Furthermore, the compressive strength values recorded were 13 MPa for grout and 7.9 MPa for gypsum. The fracture toughness values were found to be 0.09 MPa $\surd m$ for grout and 0.01 MPa $\surd m$ for gypsum. The rate of loading during the experimental tests was set at 0.05 mm/s, which was considered too low to satisfy the static loading criteria. Additionally, the laboratory tests helped calibrate the PFC modeling results, allowing for a detailed study of the shear behavior of the grout-gypsum interfaces. The number of channels in the specimens created suitable interfaces, which influenced the shear failure mechanisms and fracturing patterns for both sample types. Tensile cracking can occur at these interfaces and may propagate throughout the channels. As the number of channels increases, the volume of injected gypsum in the specimens also rises. This increase raises the crack initiation stress, failure stress, shear stiffness, and the number of fractures. Moreover, the shear stiffness and shear strength of the grout injection channels were found to be greater than those of the gypsum channels. Overall, there was a strong correlation between the experimental and numerical results.