Randomly numerical simulation of water flow field in fractured rock mass with finite element method

The water flow problem in fractured rock mass, in which the fracture aperture is distributed randomly, is simulated by using finite element method. The fracture apertures of model elements are generated randomly according to the average value and standard deviation of fracture aperture; and material parameters and element properties are changed by ANSYS parameter design language. The equivalent transmissivity of fracture is computed according to flow flux through some section computed by FEM and Darcy law; and the relationship between the equivalent transmissivity and roughness of fracture is presented. The numerical simulation investigation shows that compared with straight and smooth fracture, the equivalent transmissivity of fracture with rough surface will decrease slightly. For the investigated fracture model with 0.5 mm average aperture, the equivalent transmissivity of fracture with different standard deviations of fracture aperture changes only 5 % while the standard deviation of fracture aperture fluctuates from 0.01 mm to 0.2 mm. Traditional governing equation of water flow can not accurately depict the transform principle of water through rough fracture because the definition of pressure water-head in the equation ignores the velocity item.