A large-size experiment of unloading coal-rock mass is used to study the failure process resulted from deformation when subjected to static load, impact dynamic load and superposition of static-dynamic load by means of numerical simulation. Firstly, the mechanical model of dynamical excavation in circular tunnel with nonuniform geostress is explored, the distribution law of initial stress and the processing method for unloading are studied, and burst failure mechanisms in coal and rock is investigated. The three-dimensional numerical simulation of unloading coal-rock mass is built, then the burst failure in unloading coal-rock mass under static and dynamic loading is investigated and analyzed. The numerical simulation results showed that the important effect of impact dynamic load on the unloading coal-rock mass is shock wave repeating actions, which cause both tunnel sides shear failure to rib spalling and top strata tensile failure at large range to roof splitting. The influence of loading rate on the impact characteristics of the tunnel is notable, which is mainly embodies in the peak of failure load, the destruction regions, and the destruction types. In unloading coal-rock mass, the influence degree about superposition of static and dynamic load is larger than that of single one.
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