The Development Of Unified Pipe-interface Method And Its Application On Grout Flow In Fractured Rock Mass

Grouting is an important method to control the large deformation of surrounding rock,water inrush,mud inrush and other major geological disasters during the construction of tunnel(roadway),which crosses high in-suit stress region,fault fractured zone and other complex geological area.At present,many research results about grouting have been obtained and many engineering problems have been solved.However,due to the concealment of grouting engineering,especially when it is applied to complex underground rock environment,there are still some key scientific problems and engineering technical problems to be solved in the research of grouting diffusion mechanism and application.This paper proses a novel Unified Pipe-Interface Element Method(UP-IEM).UP-IEM overcomes the difficulties to consider the rock matrix permeability in traditional discrete fracture network model.Also,the interface element is introduced to simulate the fracture propagation.Neither local crack propagation criteria nor tracking algorithms are required compared with traditional FEM and DEM,which has quick computation and high efficiency.The research was funded by the National Natural Science Foundation Key Projects of China(Grant No.51734009).The main research achievements are following:(1)In terms of numerical method construction,this paper establishes the seepage model and algorithm for fracture porous dual medium with complex fracture network and proposes the method to equal the 2D and 3D fractured porous medium into 1D pipe model.UP-IEM uses the same mathematical model to calculate the fluid flow in both fractures and rock matrix,avoiding the hydraulic exchange between fracture and rock matrix and make computation simple.The interface element is used to simulate the fracture propagation,which could solve the problem that the traditional finite element method is difficult to simulate the fracture propagation of complex fracture network.Several typical benchmarks are simulated to verify the accuracy of UP-IEM.(2)In terms of numerical method programming,a semi-explicit method is proposed in the frame of UP-IEM based on the implicit model and explicit model.The semi-explicit method is adopted in the assembling of interface element stiffness matrix and solving coupling problem.This semi-explicit method avoids the loss of robustness caused by implicit solution and the long computation time of explicit solution.It has the advantages of simple calculation process,good convergence and strong stability.(3)In terms of grout flow,the grout flow in 3D fractured rock is simulated using UP-IEM.This paper establishes the Newtonian fluid model and Bingham fluid model and proposes the method for simulation the time-dependent viscosity and filtration.This paper effectively evaluates the grouting distance and grouting stability time of time-dependent viscosity grout and reveals the grouting flow mechanism of time-dependent viscosity grout and filtration grout in fractured rock.(4)In terms of hydro-mechanical coupling grout flow in fractured rock,a whole process dynamic analysis of grout flow and fracture propagation during fracturing grout is carried out.The influence of rock tensile strength,fracture energy,flow rate and in-suit stress on fracture propagation direction,grout flow range and grout pressure are analyzed.This paper establishes the simultaneous and sequence fracturing grout for multi borehole,obtaining the grout flow law under different borehole space and grouting time interval and revealing the hydro-mechanical coupling grouting flow mechanism.