Material point method with a strain-softening model to simulate roof strata movement induced by progressive longwall mining

Numerical simulation is an effective way to study roof strata movement induced by progressive excavation in longwall mining. However, establishing an effective and plausible numerical model is still of great difficulty, as the roof strata movement involves a complex geomechanical process. In this study, we develop a numerical tool based on the material point method (MPM) and strain softening constitutive model. Using this tool, numerical examples are conducted to demonstrate the capability of the numerical tool to simulate the roof strata movement. According to the numerical results, we obtain the following conclusion: 1) through comparison of the physical simulation experiment, the developed numerical tool is proved to be capable to simulate the complex physic processes involved in the roof strata movement, including roof deformation, shear and tensile fracture initiation and arbitrary propagation, roof fragmentation, caving and collapse, roof subsidence and contact with gob fragmentation; 2) the developed numerical tool can simulate the extremely large deformation (plastic flow) of the backfill under the same numerical framework, which is advantageous to study the mechanical interaction between the large deformation of the backfill and the roof subsidence; 3) both cross joints and layer interfaces have a significant effect on the extent of the roof collapse. The caving height is mainly affected by the layer thickness, while the vertical cross joints have a certain influence on the roof collapse in the horizontal direction. According to this study, we believe that the developed numerical tool is also beneficial for studying other excavation problems in underground, e.g., various mining methods, tunneling, cave construction, etc. Extending the numerical tool to 3D is straightforward. However, the computational efficiency should be enhanced.