Three-Dimensional Numerical Simulation Of Grouting In Stochastic Fracture Network Of Dam Bedrock

Dam foundation involving numerous fractures with stochastic distribution constitute an important concern in hydraulic and hydropower engineering.These fractures constitute flow pathways and can lead to consequences of large magnitude and pose a hazard to both human health and property security.Curtain grouting is the most popular technique undertaken to prevent the dam foundation leakage by building the foundation impervious curtains.Due to the engineering invisibility and the fracture complexity,theoretical development of grouting is severely lagged behind engineering progress.With the development of computer technology,numerical simulation method emerged as a viable option to study the grouting in fractured rock mass increasingly.Research on grouting simulation in fractured rock mass is of greatest importance for grouting construction in hydraulic and hydropower engineering on the theoretical and practical aspects.Aiming at the grouting problems in fractured rock mass,a numerical simulation method of three-dimensional discrete element is applied based on the mathematical model of grouting diffusion,in-depth analysis on the problems mentioned above and the achievements are shown as follows.(1)A grouting mathematical model for fractured rock mass is proposed.According to the grouting rheology theory,N-S(Navier-Stokes)equations and the continuity equation,the mathematical model of grouting diffusion for Newtonian fluid and Bingham fluid in fractured rock mass is presented and the influence factors of grout spread regularities are analyzed detailedly.The correction factor of roughness f and the deformation of aperture ?u are introduced,and the grouting diffusion models that considering the roughness or the hydro-mechanical coupling are provided respectively.(2)A three-dimensional stochastic fracture network model coupled with boreholes is established based on the Monte-Carlo method.According to the fracture exploration data of a powerhouse dam section,five sets of fracture parameters with stochastic characteristics are selected by the Monte-Carlo method and the optimal combination of simulated values is obtained according to the “minimum relative error principle”.The three-dimensional stochastic fracture network model coupled with boreholes is built,including the single-hole model and the multi-hole model.And the tetrahedron finite difference grid technology is adopted to establish the discrete model of fracture grouting.(3)Parameter sensitivity analysis and hydro-mechanical coupling analysis of numerical simulation of single fracture grouting.Based on single fracture characteristic model and parameter sensitivity analysis method,the influence laws that seven main factors exert on the simulation results are studied.The hydro-mechanical coupling and non-coupling comparative analysis is carried out on three factors of fracture dip angle,fracture aperture and grouting pressure.The results show that the discharge per unit width of slurries is sensitive to fracture aperture,slurry viscosity,grouting pressure,etc.The deformation of fracture aperture is sensitive to grouting pressure and fracture with large inclination.The influence degree of hydro-mechanical coupling on grouting simulation results is related to the value of influencing factors.(4)Numerical simulation analysis of three-dimensional stochastic fracture rock mass grouting in the dam foundation with the consideration of fracture aperture random distributions.Based on the single-hole grouting model,grading perfusion of cement grout is simulated,and law that grout diffuses in three-dimensional stochastic fracture network is studied.Based on the multi-hole grouting model,sequence grouting method is proposed and the influence law of grouting sequence making on slurry diffusion is studied.Through comparing the grouting quantity and grouting time of simulation with the actual value,the feasibility of this method is verified.This approach can be applied to the similar curtain grouting engineering,which can provide guidance for scientific grouting design.