Investigation on the shear behavior of thin-layer grouted joints: discrete element analysis and analytical model

As a common geological structure in engineering, the current research on the shear deformation characteristics of grouted joints remains confined to laboratory experiments. Establishing a shear analytical model for grouted joints holds significant theoretical value. Focusing on thin-layer grouted joints, this work investigated the macro-mechanical properties and micro-fracture behavior of thin-layer grouted joints under shear loads numerically by generating discrete element method (DEM) models with the particle flow code in two dimensions (PFC^2D). The shear process was divided into three phases: compressive and elastic deformation (Phase I), strain hardening and softening (Phase II), and residual deformation (Phase III). Subsequently, by decomposing the shear deformation in Phase I into closure compression of the grout layer and elastic deformation of the composite load-bearing structure composed of the cement mortar skeleton and rock, an analytical solution for the shear behavior in Phase I was derived. In Phase II, homogenization theory was utilized to model the thin-layer grouted joint as a macroscopically isotropic material composed of multiple anisotropic composite elements. To predict strain hardening and softening behavior, a three-parameter modified damage model was developed using damage theory. Finally, the proposed analytical model was validated through comparisons with numerical simulation results and direct shear test results from other studies, accompanied by a discussion of the model parameters.