Study On Characteristics Of Water And Sediment Flow In Weakly Cemented Fractured Rock Mass Based On Particle Flow Method

The coal resource is very rich in western China, accounting for nearly 80% of the total in China, but the shallow buried coal seam in the area is covered with weak cementation layer and loose aquifer. Water and sediment disasters are prone to occur in the mining process, which seriously threatens the safety production of the mine. Therefore, the research on the law of water and sediment flow in fractured rock mass has important theoretical and practical significance to the safety of coal mining in West China.In this paper, the theoretical analysis of water and sediment two-phase flow in fractured rock mass is carried out by the lattice Boltzmann method and multiphase flow theory. Numerical analysis of the mechanical properties of fractured rock, starting rule of accumulation sand, sediment flow rule, and the thick unconsolidated layers above the roof collapse caused by mining. Main research works are as follows:(1) Research on the relationship between particle flow simulation parameters and macro parameters. The influences of the contact stiffness, bond strength, friction coefficient, void ratio, stiffness ratio and the coefficient of viscosity on the macro mechanical behavior were analyzed by numerical simulation; Relevant parameters of the water and sediment flow in fractured rock mass were calibrated, such as the contact stiffness, bond strength, friction coefficient and coefficient of viscosity.(2) Analysis of structural characteristics and mechanical properties of weakly cemented jointed rock mass. The composition and the degree of cementation of weakly cemented rock were analyzed from the microscopic point of view; The numerical model of intact rock and fracture rock was established based on particle flow method, the strength properties and deformation characteristics of the intact rock and the cracked rock are analyzed; The mechanical constitutive equation of weakly cemented rock was established. The study shows that the existence of cracks has important influence on the morphology and the location of the failure surface. The existence of cracks makes the rock mass peak strength, residual strength and initial elastic modulus decrease which reduced rock mechanical properties.(3) Lattice Boltzmann model of water and sediment flow in fractured rock mass was established. The basic conservation equations of water and sediment were derived based on lattice Boltzmann method; The control equation of the water and sediment flow system was established; Based on the immersed boundary method, the water and sediment interface of the was analyzed by using the Euler point and Lagrange point; Particle impact mechanics model is obtained based on the discrete element method.(4) Analysis of movement law of water and sediment particles in fractured rock mass. Theoretical analysis of the incipient velocity of sand, and got the sand threshold velocity; Numerical simulation of sand grains start, get the rule of sand accumulation in the starting process; Numerical simulation of sand inrush in fracture. Analysis of the sand flow patterns, found that the sand particles in the shape of the funnel before entering the crack, When the sand is in the crack, the "S" curve movement is made in the crack; A mechanical model of sand mining roof covered with thick loose was established; The stress intensity factor at the top of roof caving was obtained by using the theory of fracture mechanics; Analysis of the water pressure and flow rate of water and sediment in the water inrush channel; After the water flow into the cracks, the rock mass structure is weakened, and sand clogging fracture, which made the pore pressure of rock mass increases, and the crack expands rapidly, leading to the acceleration of roof falling.