Mechanical Effects Analysis Of The City Subway Tunnel Inverted Arch

Being an inverted arch structure set at the bottom to improve stress conditions of the tunnel's lining structure,the inverted arch is an important part of the tunnel lining structure.The role of the inverted arch is more obvious especially in weak surrounding rocks with a larger lateral pressure coefficient,or surrounding rocks with a large horizontal tectonic stress or with conspicuous flowing deformation,or swelling rocks.On the one hand,the inverted arch needs to effectively transfer the tunnel's upper stratum pressure and the pavement load to the ground.On the other hand,it should resist against the counter-force from the tunnel's lower stratum.Thus,a proper setting of the inverted arch can effectively control the deformation range and influence scope of the tunnel surrounding rock,improve the form of stress on the lining structure,and coordinate the axial force and bending moment distribution of the lining structure.In primary lining of the tunnel,the inverted arch can not only reduce settlement deformation caused by inadequate bearing capacity of the tunnel foundation,but also prevent the heaving floor from swelling deformation and adjust the role of the lining stress.Wang et al.studied mechanical behaviors of the tunnel inverted arch by combining the large-scale model experiment with the infinite analysis.Results suggest that the tunnel inverted arch is essential to improve the bearing capacity of the tunnel structure,restrain the internal plastic zone of the surrounding rock and the displacement around the tunnel from further expansion,and promote safety of the lining structure.In order to study the mechanical effect of the inverted arch of the expansive soil layer,Midas,one kind of finite element analysis software,analyzed the following:(1)The numerical simulation of the bottom support form of the tunnel is carried out,the numerical simulation of the bottom support form of the tunnel is carried out.(2)The vertical displacement,vertical stress,shear stress and plastic zone of tunnel surrounding rock are compared and analyzed in the construction of full-span tunnel and the construction of half-span construction.The results show that theconstruction of half-span construction of inverted arch tunnel is relatively good,it can effectively suppress the bottom of the tunnel is deformed,reduce the compressive stress at the arch and arch feet,and control the plastic zone of the surrounding rock,which can improve the mechanical performance of the lining structure.(3)By analyzing the best inverted arch radius to find the most reasonable radius value.(4)Based on the CRD method,pre-filling slurry by tubes field information construction monitoring strictly in the process of grouting at present,Early warning and treatment of ground settlement,ensure the safety of construction.