The Study Of The Numerical Simulation Method For The Pre-grouting Reinforcement Of Fractured Weak Surrounding Rock Mass Ahead The Tunnel Face Based On Numerical Manifold Method

With the launch of the develop-the-west strategy,an ever-increasing demand for the infrastructures of transportation,energy and water has risen,which leads to a large amount of deep underground engineering projects in the west of China.Owing to being with high efficiency,high safety and environment friendly,the full face tunnel boring machine(TBM)has been widely employed in the above engineering projects.However,due to the inability of TBM in being adapted to bad environment,especially in the deep burying long tunnels,the TBM will be subjected to many challenges,such as TBM falling,TBM jamming,the falling of tunnels and the large deformation of tunnel.So how to keep the TBM works well has been the key study of the rock mechanic and rock engineering.In addition,the grouting method,which is one of the most used reinforcing method in the tunneling engineering,has been studied by many scholars.However,in the current study to grouting in the deeply buried tunnels,the analytical method,laboratory tests or field tests are challenging in uncovering the mechanism of grouting around the surrounding rock of deeply buried tunnels due to the heterogeneity of rock mass as well as the invisibility of the grouting behind the surrounding rocks.With the rapid development of computer science,the Numerical Manifold Method(NMM),which is a typical hybrid continuum-discontinuum method,has been widely used in the study of tunnel surround rock related problems due to its ability of dealing with the continuous problem and discontinuous problem in the same analytical structure.Thus,in this study,based on the NMM,the algorithm based and hardware based method a used to improve the computing efficiency of NMM.based this improved NMM,a method for the simulation of pre-grouting in the fractured weak rock ahead the tunnel face is proposed and the main work includes the following four parts:(1)Adoption of cohesive element method for high efficiencyIn this study,a Voronoi grain based NMM model is used to better simulated the process of rock failure,meanwhile to avoid the time-consuming contact related computation,a cohesive element model is introduced for a high efficiency;in addition,to guarantee the stability of simulation during the rock failure process,which is a typical continuum-to-discontinuum process,a stability algorithm is proposed.And based on the simulation results of corresponding numerical samples,the ability to simulate the rock failure processes and high efficiency of this improved NMM(Co-NMM)is verified.(2)A CUDA based GPU acceleration algorithmDue to the serial architecture,the Co-NMM program can hardly be accelerated by the computer parallel servers.Thus,in this study,based on the Compute Unified Device Architecture(CUDA),the Co-NMM is parallelized,debugged and verified.In addition,several optimizing technique,including data consolidation,separation of sub-routines,divergence consolidation and adoption of single precision computation,are adopted to further improve the computation efficiency of the parallelized Co-NMM,which is the developing platform for the following tunnel excavation algorithm and pre-grouting reinforcement algorithm.(3)A simulation platform with high performance for tunnel excavationdue the limitation of the original excavation algorithm of NMM,including the time-consuming process of stress balance,unclear relationships between softening process and real excavation process,the neglect of the influence of original fractures in the surround rock mass,some approaches are proposed to solve the limitations above after the parallelization of the original excavation algorithm.First of all,the implicit Co-NMM is used to accelerated the process of stress balance;then,the stress state of surrounding rock of TBM tunnel is used as the intermediate variable to map the softening process and real excavation process;at last,a Monte Carlo based random fracture generation code is introduce into the pre-process code of NMM to simulate the influence of original fractures on the surround rock mass during the excavation process.By taking above improving approaches,a better tunnel excavation simulation platform than the original one is developed.(4)Simulation of pre-grouting reinforcement of the weak surrounding rocksBased on the developed tunnel excavation simulation platform,an algorithm for the pre-grouting reinforcement of the weak surrounding rock in the deep buried tunnel is proposed.First of all,a grouting hole generating method in the numerical deep buried tunnel is proposed.Then,the detection algorithm of grouting networks from existing fractures are proposed to confirm the channels where the grouting is flowing in.After that,a Bingham laminar flow model between smooth parallel plates is introduced to simulated the behavior of grouting in the flowing channels.After the simulation of transport process of grouting,based on the cohesive elements,the reinforcement algorithm is proposed.After the coding and debugging,several numerical models are simulated and compared with the analytical and experimental results,based on which this developed pre-grouting program is verified.At last,the simulation results of excavations between reinforced tunnel and unreinforced tunnels are compared,and ability of the developed pre-grouting program to simulated the pre-grouting process and reinforcement of surrounding rock is verified.