Study on direct shear mechanical characteristics of grouted-filled jointed coal using discrete element method

Grouting is a widely used technique in underground engineering by enhancing mechanical properties of jointed rock mass. Understanding the shear characteristics of jointed coal mass after grouting reinforcement is crucial for optimizing grouting parameters and advancing grouting mechanism. This study proposed a grout-filled jointed coal (GJC) direct shear discrete element model (GJCS-DEM). The model consists of coal matrix, grout-filled layer, and coal-grout interface. Parallel bond model (PBM) was adopted on intact coal matrix and grout-filled layer, while smooth joint model (SJM) was utilized to model deform behavior of interface in this model. Then, microscopic parameters determination method for SJM in GJCS-DEM has also been introduced and all the parameters for PBM and SJM were calibrated. After that, the proposed approach was validated through the good agreement between strength and failure characteristics of numerical and experimental direct shear test results of specimens with different grouting materials. Finally, the validated GJCS-DEM was applied to investigate effect factors of shear mechanical propertied for GJC specimens. As the grout-filled layer height and joint sawtooth dig angle increases, both peak and residual strength increases, while the failure pattern varies. The work here can offer valuable insights for grouting efficiency improvement in engineering practices.