| The 21st century is a century of great development in tunnels and underground space.With the planning and construction of a number of century projects represented by the downstream project of the the Yarlung Zangbo River and the Sichuan-Tibet Railway,the tunnel engineering construction in China has entered a new era."From hills to deep mountains,from the mainland to the border",the engineering construction is facing increasingly complex terrain and geological conditions,and the safety construction is facing huge challenges.Tunnel surrounding rock collapse disaster is one of the most common geological disasters in jointed hard rock tunnels,characterized by strong concealment,strong suddenness,strong destructiveness,and strong catastrophic nature.The disaster process involves gradual destruction of jointed rock masses and large-scale collapse of dangerous block groups,which is extremely difficult to prevent and control,causing serious economic and property losses and casualties every year.Especially under the coupling effect of groundwater and ground stress,the risk of tunnel surrounding rock collapse disaster is further exacerbated.It is urgent to carry out research on the mechanism of tunnel surrounding rock collapse disaster under the hydraulic coupling effect to provide theoretical basis for the prevention and control of tunnel surrounding rock collapse disaster.Focusing on the simulation method and engineering application of tunnel surrounding rock collapse disaster under hydraulic coupling,this paper comprehensively adopts case analysis,indoor test,theoretical analysis,numerical simulation and other means to carry out research.Firstly,this paper studied the optimal value of control parameters in 3D DDA and determined the optimal value area of time step and contact spring stiffness in 3D DDA.Then,this paper proposed the virtual block removal algorithm and the bolt real-time support algorithm and formed the 3D discontinuous deformation analysis method considering the tunnel excavation support(3D DDA_ES).Then,this paper carried out the normal stress shear experiment of rock mass discontinuity under different water content and filling degree,and proposed the weakening model of structural plane mechanical parameters considering filling effect.This paper studied the fluid-structure coupling simulation method based on 3D DDA and SPH and the interaction between DDA block and SPH particles is systematically described.Lastly,tthis paper analyzed the influencing factors of water inrush disaster caused by collapse chain of tunnel surrounding rock,which can provide theoretical basis for active prevention and control of tunnel disasters.The main research results include:(1)Regarding the construction of complex block system models and the selection of control parameters in three-dimensional discontinuous deformation analysis methods,this paper developed the pre-processing program for 3D discontinuous deformation analysis method by combining Auto CAD and Open TK.Based on the theoretical derivation,this paperthe analyzed the influence of time step and contact spring stiffness on the 3D DDA numerical calculation results emphatically.Secondly,the influence mechanism of time step on 3D DDA calculation results is studied by using the two-block free-fall model,and the reasonable value area of time step length is determined.Then,considering the contact effect between the blocks,this paper studied the combined influence mechanism of time step and contact spring stiffness on the 3D DDA calculation results based on the the doubleblock sliding model,and analyzed the error between the 3D DDA calculation results and the theoretical value under different time step and contact spring stiffness combination conditions,Based on the error,this paper devided the combined value area of time step and contact spring stiffness into four zones to determine the optimal value area of time step and contact spring stiffness,which are Q1,Q2 Q3 and Q4.The research results can provide effective reference for the application and development of 3D DDA method.(2)In response to the difficulty of simulating the tunnel excavation process using traditional 3D DDA methods,this paper proposed the virtual block removal algorithm,in which the excavated blocks are moved out of the calculation area under the condition of ensuring the consistency of the array,and the algorithm is embedded into the original 3D DDA program,and an improved 3D DDA method suitable for tunnel and underground engineering excavation simulation(3D DDA_EXC)is developed.Secondly,based on the free falling model of static block and the free falling model of sliding block,the theoretical calculation results and 3D DDA_EXC are compared and analyzed,whihc verified the accuracy of 3D DDA_EXC method.Then,based on the 3D DDA_EXC method and the DEM method,this paper simulated the massive rock mass tunnel excavation,and compared and analyzed the rock deformation around the tunnel.The results are basically consistent,which further explains the feasibility of 3D DDA_EXC method in simulating tunnel excavation.(3)Regarding the dynamic support of anchor rods in the 3D DDA method,this paper proposed the real-time support algorithm of bolt,which is embedded to the 3D DDA EXC method and construct an improved 3D DDA method considering tunnel excavation and support(3D DDA_ES).Then,this paper carried out tunnel excavation and support simulation based on the Huangjiazhuang Tunnel of the Lunan High-speed Railway,analyzed the key block movement during tunnel excavation and support and the evolution process of the bolt axial force,and finds that the left and right sides of the tunnel The axial force of some bolts at the right arch foot is small,which has little impact on the stability control of the block.This part of the system bolts can be canceled during the actual construction process.(4)Regarding the weakening mechanism of rock mass structural planes under water conditions,this paper studied the influence mechanism of the water content of the filling structural plane and the thickness of the filling material on the shear performance of the rock mass structural plane.Firstly,the specimen mould with rough structural plane is prepared by 3D printing technology,and the standard cement mortar specimen with rough structural plane is prefabricated.Secondly,relying on the multi-function rock shear testing machine,this paper carried out the normal stress shear test(CNL)of specimens with different water content and filling degree of weak structural plane,analyzed the influence mechanism of water content and filling degree of weak structural plane on the peak shear stress and shear strength of rock structural plane,established the calculation model of shear strength of jointed rock mass considering the hydraulic weakening effect,and embed it into 3D DDA_ES method,a three-dimensional discontinuous deformation analysis method considering the weakening of structural plane mechanical parameters is formed.(5)Aiming at the problem of two-phase medium coupling analysis and simulation in the collapse disaster of tunnel surrounding rock under hydraulic coupling,this paper proposed the 3D DDA-SPH fluid-structure coupling simulation method to simulate the whole process of tunnel excavation and support.Firstly,the interaction between DDA block and SPH particles is comprehensively described from the aspects of contact retrieval and mechanical transfer,and the coupling mechanism between DDA block and SPH particles is analyzed.Secondly,the numerical simulation of shock wave test and rigid ball water penetration test was carried out,and the simulation results and test results of 3D DDA-SPH were compared and analyzed,which verified the accuracy of 3D DDA-SPH coupling method in solving fluid-solid coupling problems.(6)Regarding the unclear mechanism of tunnel surrounding rock collapse disaster under hydraulic coupling effect,this paper analyzed the influencing factors of the water inrush disaster caused by the collapse chain of the tunnel surrounding rock based on the 3D DDA-SPH coupling simulation method,and the evolution process of the water inrush disaster caused by the collapse chain of the tunnel surrounding rock under the conditions of different tunnel face block modulus,drain hole diameter and construction method was emphatically studied,and the influence mechanism of the tunnel face block modulus,drain hole diameter and construction method on the stability of the water-resisting rock mass of the tunnel face was revealed,which provides a theoretical basis for the prevention and control of water inrush disasters caused by collapse chain of tunnel surrounding rock. |
