Dynamic Construction Simulation Of Fault Fractured Zone In High Risk Railway Tunnel

As one of the common engineering geological conditions in tunnel construction,fault fracture zone has broken rock mass and poor self-stabilization ability of surrounding rock.Because of the inaccurate location of predicted mileage by design data or the poor effect of design support,it is prone to large deformation of surrounding rock,destruction of tunnel structure and even collapse,which greatly increases the risk of tunnel construction.Dengjiawan Tunnel of Chengdu-Kunming Railway is a typical high-risk railway tunnel.The tunnel has a large buried depth and excavation span,and the line passes through several fault fractured zones.The construction is difficult and the construction technology is complex.This paper supported by the Science and Technology Research and Development Project of China Railway 21 Bureau（19C-4）,based on TSP method which can accurately identify the fault fracture zone and the unique advantages of FLAC^3D in geotechnical engineering simulation,combined with advanced geological prediction and numerical simulation,this paper studies the construction process of tunnel crossing surrounding rock around Yakoucun fault fracture zone,and analyses the distribution law of surrounding rock displacement,initial support displacement and plastic zone under different excavation footage and excavation support modes.Suggestions are made on the construction parameters across the fault fracture zone safely and quickly.The main conclusions are as follows:（1）The location of Yakoucun fault is detected by TSP advanced geological prediction method,and the results are consistent with the geological conditions revealed by DK381+454 excavation.The physical and mechanical parameters of rock mass are extracted based on TSP.（2）The numerical simulation of three-step construction in front of fault fracture zone shows that the deformation of surrounding rock increases with the increase of excavation footage,but at the boundary of fault fracture zone,the longitudinal horizontal displacement reaches the minimum value under the condition of 2.4m footage.It shows that the number of excavation disturbances has a greater impact on the surrounding rock deformation than the excavation footage.Therefore,it is suggested that the excavation footage of the tunnel in front of the fault breakage zone should not be too small.（3）The numerical simulation of rock mass deformation in fault fracture zone during tunnel excavation shows that there is an inflection point at 3.0m in front of the boundary of fault fracture zone without advanced support,so the advanced grouting support distance can be chosen as 3.0m.The safe distance between the face of grouting face and fault fracture zone is 1.0m.（4）According to the support parameters of 1.0m safe face distance and 3.0m advanced support range of fault fractured zone,the construction simulation shows that the advanced support mode of vault+tunnel face Grouting greatly improves the stability of surrounding rock of fractured zone.（5）The numerical simulation of three-step construction in fault fracture zone shows that the vertical and horizontal displacement of surrounding rock does not increase with the increase of excavatio n footage;when the footage is 1.0 m,the deformation of surrounding rock is the smallest,and when the footage is 0.8 m,the deformation of surrounding rock is the largest.It shows that the number of excavation disturbances is also an important factor affecting the deformation of surrounding rock in fault fracture zone.Therefore,the excavation footage within the fault fracture zone of this tunnel is recommended to be 1.0m.