Study On Stability Of Excavation Face Of Large Section Tunnel Through Reservoir In The Fault Fracture Zone

With the rapid development of transportation industry in China,the tunnel is widely utilized because of its advantages in running across the terrain,shortening the mileage,reducing urban land use and not being affected by climate and so on.At the same time,China's topography is varied and complicated.It often occurs that the tunnel encountered the fault fracture zone in the process of tunnel construction.The surrounding rock of fault fracture zone is characterized by poor mechanical properties,fracture development and good permeability,and it provides a good permeability path for underground water.The collapse of tunnel face,water and mud bursting engineering accidents are easily happen in the process of excavation in water-rich soft ground.It has important practical significance and theoretical value to study the mechanism of instability.Based on the Zhongzhai tunnel in Guiyang city,Guzhou province,through theoretical analysis and numerical simulation analysis to study the stability of tunnel face,the main work and the results are as follows:(1)The applicable scope of the surrounding rock pressure calculation based on the silo theory is obtained by analyze the characteristics of a variety of surrounding rock pressure calculation formula.The strength reduction method is introduced,considering the influence of seepage of groundwater,with the help of complex function to build a tunnel face instability model to analyze the stability coefficient of tunnel face under water,getting underwater tunnel face stability coefficient and expression of supporting force.The stability coefficient of tunnel face is less than 1 by calculation.By the relationship curve between support pressure and stability coefficient,for high water conditions,increasing the support pressure is not obvious to improve the stability of working face.(2)Based on Horm model of sliding body,and introducing double reduction factor,we establish two models of tunnel face stability near the fault fracture zone.The differences of dip angel of fault mud to stability coefficient of tunnel face in fault fracture zone and the relationship curve of tunnel face stability coefficient with tunnel face advancing are obtained by calculation.The result shows that,with the increase of the dip angle of fault mud,tunnel face stability improved in the fault fracture zone;in the process of construction,the overall stability of tunnel face has different sensibility with excavation depth,with the increase of the dip angle of fault,the face advancing has greater influence on stability coefficient.We analyze the impact of changes in the friction angle of the intact rock and fault gouge on tunnel face stability coefficient by improve the wedge sliding body model to bulid a double-broken line sliding model,the result shows it can be simplified to one inclined sliding surface to calculate the stability coefficient when the internal friction angle of rock and soil mass is different than the one.(3)Based on the strength reduction method and nonlinear failure criterion,by using the limit analysis upper bound method to analysis the stability of tunnel face.We established failure model of tunnel face for energy consumption calculation,and get the Analytical solution of safety factor of tunnel face.With the aid of the optimization tool,the relation curve between the parameters and the stability coefficient is obtained,the result shows that tunnel face stability decreasing with the increasing of tunnel buried depth,soil bulk density and nonlinear coefficient.(4)We study the influence of excavation and the dip angle of fault mud on the stability of tunnel face in the fault fracture zone based on numerical simulation method,and the result shows that there is loose circle face upper rock body form a silo shape in the process of construction,which is closer to the theoretical hypothesis.With the increase of the dip angle of fault mud,the face of axial displacement,internal force of support structure along the axial changes more obviously near the fault fracture zone,more prone to accidents in the fault fracture zone,which is consistent with the theoretical analysis.