| There are many researches about the law of cavern influence on tunnel segments and surrounding rock at home and abroad,but studies have typically focused on the cavern's influense in the construction stage and deep buried tunnel like highway tunnel and mountain tunnel.There is few studies on the full life cycle activity and shallow buried tunnels in soft rock layer.Soft rock has a strong time dependent characteristics,including creep,strain rate dependence and stress relaxation,which will have a lasting impact on the tunnel in the long-term service.In order to study the stress state of the lining of soft rock tunnel in the presence of caverns,the finite element method(FEM)is adopted in this paper to study the law of the cavern influence on tunnel segments' internal force and deformation in different work conditions like different cavern positions,different size of the caverns,different groundwater condition,different earth pressure coefficient and different cavity treatment measures.The conclusions can be obatained as follow:(1)Without consideration of the fluid-soil coupling,the effect of the cavern on the stress and strain of the surrounding rock is very small.In addition,cavern has little effect on tunnel segments' axial force in a short period of time after the cavern has appeared.But cavern has a larger long-term effect on tunnel segments' moment,which is the main reason of segments' yielding and crack.(2)The existence of cavern will make surrounding rock occur larger shear stress,resulting in soft rock dilatancy and creep.It will lead to redistribution of internal force of segment,which is not conducive to the tunnel structure stable.For different positions of caverns,the influence of the hance cavern is the largest,that the negative moment peak of the segment appears in the middle of cavern.the influence of the arch shoulder is intermediate and the influence of the vault is the smallest.(3)For the caverns in different sizes,the smaller cavity,the tunnel lining ‘s deformation trend to the tunnel side.With cavern increase gradually,the positive moment of lining in cavern range becomes smaller,deformation gradually transformed from to the tunnel side into to the cavern side,outside segment would be tensed.(4)under the condition of fluid-soil coupling,the dissipation of excess pore water pressure,which increase the confining pressure around the tunnel,make the tunnel segments endure greater internal force.The fluid-soil coupling algorithm can simulate the excess pore water pressure's dissipation process in soft rock,which is suitable for used to simulation the stress and deformation.of pipe jacking tunnel in excavation and service process in rich water soft rock layer.(5)Caverns will destroy the tunnel originally balance loading mode.In order to obtain stable,the angle position between cavern and segment will bear huge concentrated stress.Such adverse force pattern will aggravate the growth rate of the bending moment of the segment,and the segment in the cavern position would achieve the yield moment in advance. |
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