Mining-induced shear deformation and permeability evolution law of crushed rock mass in fault zone

To explore the mechanism of water inrush induced by fault activation under mining, experimental studies were conducted on the shear deformation and permeability evolution of crushed rock mass in fault zone. Specifically, a set of compression-shear-seepage test system for crushed rock mass was designed according to the principle of fluid-solid coupling, with the coupling process of shear deformation and seepage realized. On this basis, the shear-seepage coupling test was carried out for the crushed rock mass under the influence of multiple factors. Thus, the influence of particle size distribution and initial porosity of crushed rock mass on porosity and permeability parameters during continuous shearing process was obtained. According to the experimental results, the change process of permeability and porosity of the crushed rock is generally same under the continuous shear conditions, which can be divided into three stages: (1) the slowly increase stage, which reflects the process of crushed rock particles adjusting from scattered state to a certain organizational structure under confining pressure and shear stress; (2) the accelerated increase stage that reflects the shear swelling process of crushed rock under shear stress; and (3) the slowed increase stage, during which the crushed rock particles will finally reach dynamic equilibrium under the constraint of confining pressure. The sample with smaller Talbot index or larger initial porosity has higher permeability and porosity sensitivity, as well as greater permeability and porosity. However, the evolution law of β factor of non-Darcy flow is opposite to that of permeability. Through numerical simulation, it is found that the migration of rock particles within the shear zone of crushed rock mass under shear stress is the main cause of the shear swelling. The transformation of the force chain of particles from a random distribution to a specific direction during the shear swelling of crushed rock mass, which is manifested in the swelling of local pores and pore throats, is the main reason for the increase of porosity and permeability. The research results could provide reference for the revealing of water inrush mechanism and prevention of water inrush in the deep coal mines.