Seepage Analysis Of Fracture Rock Masses Based On Random Field Theory

The phenomenon of fracture seepage is common in engineering fields such as water conservancy and energy protection,and it is related to the safety and stability of engineering operation,so it is significant to study the characteristics of fracture seepage.Single fracture is the structural unit of fracture network seepage,and water can flow in the fracture network by the connected channels formed between a group of single fractures.Before studying the seepage characteristics of the overall fracture network,it is necessary to understand the law of seepage characteristics of single fractures.Fractures can be divided into smooth fractures and rough fractures according to the degree of undulation of their structural surfaces,and in nature there are often only rough fractures,whose seepage is called unsaturated seepage.The study of unsaturated seepage characteristics of fractures has been a difficult problem,at present,there are mainly physical test method and numerical simulation method,both methods can obtain the unsaturated hydraulic parameters of fractures,but because the test method is not only expensive and time cost is large,more scholars choose numerical simulation method to study.This paper solves the unsaturated hydraulic parameters of the fracture,and proposes a calculation method based on random field theory and cubic law to establish the equilibrium equation of flow in each local area of the fracture,which can obtain numerical solutions with high accuracy,and the research work and results are as follows:(1)The SEEPAGE program is compiled based on C++language to calculate the unsaturated hydraulic parameters of the fracture,and the random numbers obeying log-normal distribution are generated by the covariance matrix decomposition method to describe the rough fracture,and the water filling situation of the fracture localities in drainage and suction is judged according to the capillary suction law and water-air trap effect under different matrix suction.The random number of openness and fracture local water filling are checked,and the results show that the program is feasible.The water holding curve of the fracture was obtained by applying several different sets of pressure heads at the inlet and outlet boundaries for the study of both cases of fracture drainage and water absorption,and the water filling area of the fracture was calculated based on the water filling area of the fracture.(2)The flow balance equation of each local area of the fracture is established according to the cubic law.and the head vector at the form center of each local area of the fracture is calculated by combining the boundary conditions,and the permeability coefficient curve of the fracture is obtained by applying Darcy’s law.In comparison with other solution methods,the results show that the method proposed in the paper for calculating the unsaturated hydraulic parameters of the fracture is feasible and has high accuracy.The effect of the discrete local scale of the fracture is studied,and the results show that the larger the discrete scale is,the more stable the change of the hydraulic parameter curve is,and the calculation results are more accurate.(3)Using the method proposed in the paper to determine the water holding curve and permeability coefficient curve to solve the permeation problem of the dam base of the actual project,the project was modeled and parameterized by the COMSOL software platform to simulate the unsaturated seepage phenomenon of the fracture in the project,and the pressure head evolution process at different measurement points of the dam base at different time steps and the pressure distribution of the characteristic points at the bottom of the dam base were calculated.The results show that the seepage in this project reaches steady state at 150 seconds.The rate of head change at the fracture network junction is related to the distance of the upstream head,and the maximum head values reached are different,and the simulation method realistically reproduces the water flow change in the actual fracture.(4)The fracture is simplified to an equivalent continuous type medium,and the one-dimensional ring unit model is studied again,and a method of rotating the fracture network study domain of the ring unit model is proposed to calculate the permeability coefficient tensor of the fracture rock mass,and the FNTDSM program is compiled,and the permeability coefficients in 288 directions in space are calculated,and the comparison with other algorithms shows that the method is feasible,the calculation accuracy is high,and the algorithm is optimized.