Study On Surrounding Rock Deformation And Supporting Structure Mechanical Behavior In Earth-rock Interface Shallow-buried Unsymmetrical Pressure Tunnel

In the process of tunnel construction,lining cracks and diseases in the entrance section of shallow-buried unsymmetrical tunnels have always been a problem that plagued the tunnel engineering community,and this problem will be more common in future construction.At present,the calculation method of the surrounding rock pressure of the unbiased tunnel caused by topography is very mature,but most of them only consider a single layer.The geological environment of the actual project is often the condition of the earth-rock boundary strata.This kind of strata is uneven in soft and hard,and the surrounding rock mechanics is quite different.During construction,the lining cracks caused by the uneven deformation of the two strata are prone to occur.Therefore,it is necessary to study the deformation of the surrounding rock and the mechanical behavior of the supporting structure of the earth-rock boundary section of the shallow-buried unsymmetrical tunnel.Relying on a first-class highway tunnel project in southwestern China,this thesis uses case investigation,theoretical analysis,numerical simulation,model test,field investigation to carry out the research on the tunnel’s surrounding rock deformation and supporting structure mechanics.The details are as follows:(1)Identification of main influencing factors of surrounding rock deformation and supporting structure mechanics of earth-rock interface shallow-buried unsymmetrical tunnel.By consulting related literature on shallow-buried unsymmetrical tunnels,the common geological conditions and related diseases of shallow-buried unsymmetrical tunnels are summarized,and four influencing factors that have a greater impact on surrounding rock deformation and support mechanics are summarized: surface slope,earth-rock interface inclination,The buried depth,the relative position of the earth-rock interface and the tunnel section.(2)Study on the influence law of storage conditions of earth-rock interface shallow-buried unsymmetrical tunnel.Use FLAC 3D to establish a two-dimensional tunnel model and analyze the four influencing factors on the surrounding rock deformation(vertical displacement,lateral displacement,surface displacement,plastic zone of the surrounding rock of the tunnel section)and mechanical behavior of the lining(maximum principal stress,minimum principal stress,bending Moment,axial force,safety factor of the second lining)influence law.Using the sensitivity analysis of influencing factors,it is found that soil deformation is sensitive to changes in surface slope,and the mechanical behavior of lining is sensitive to changes in the relative position of the interface and the tunnel section.(3)Model test study of earth-rock interface shallow-buried unsymmetrical tunnel.Using the similarity theory to derive the similarity relationship,the ratio of the surrounding rock material and the lining material was tested,and a group of ratios closer to the target value were obtained,and a 1:50 model test was carried out.By comparing the results of the model test and the two-dimensional numerical simulation,the laws of surrounding rock deformation and lining mechanics are obtained.(4)Numerical simulation analysis the construction of earth-rock interface shallow-buried unsymmetrical tunnel.Carry out on-site survey of the supporting project,summarize the distribution of cracks in the lining,and summarize the cracking process and distribution of the cracks.Using FLAC 3D,a three-dimensional numerical model based on the real topography of the project was established,and the change of the secondary lining stress with the excavation step during the construction phase was analyzed,and it was revealed that the tensile stress and shear stress caused by the biased pressure of the earth-rock topography were the cause of the lining cracking.Based on the supporting project,a construction suggestion is given that the best time for the construction of the second lining of the earth-rock tunnel is 24 m.Based on the results of three-dimensional numerical simulation and the distribution of cracks in the field investigation,a mechanical model of the second lining of earth-rock shallow-buried unsymmetrical tunnel was established.The lining at the deep-buried side arch waist is subjected to the combined action of shear stress and tensile stress,the lining at the shallow-buried side arch waist is subjected to tensile stress,and the lining at the shallow side wall is subjected to shear stress.