| The ground fissure in Xi’an has caused a great obstacle to the construction of rail transit and poses a great threat to the safety of tunnel construction.However,there are few researches on the settlement and deformation caused by subway tunnel construction in ground fissures,and there is insufficient relevant experience.Therefore,it is of great significance in academic and practical construction to study how to reduce the surface settlement and deformation of surrounding rock caused by tunnel construction in the ground fissure section,so as to improve the construction safety and shorten the construction period.Based on this,this paper takes the shallow buried and concealed excavation construction of Xi’an Metro Line 6 tunnel to cross the f8 ground fissure as the engineering background,and uses the methods of theoretical analysis,numerical simulation and on-site monitoring to affect the construction influence and construction method optimization of subway tunnel crossing the ground fissure.The main research contents and conclusions are as follows:(1)According to the stress characteristics of subway tunnel structure crossing ground fissure,the simplified mechanical and displacement models of the integral long tunnel and the integral short tunnel through ground fissure are established.According to the structural mechanics displacement method and elastic foundation beam theory,the structural internal force and deformations of integral short tunnel in the hanging wall and the footwall of ground fissure are analyzed and calculated respectively.The calculation results show that the bending moment and shear force of tunnel structure reach the peak at the ground fissure.(2)Through MIDAS GTS / NX,the numerical calculation model of tunnel crossing ground fissure was established,and the CRD method was used for excavation simulation.The surface transverse settlement,surface longitudinal settlement,vault settlement,tunnel convergence and surrounding rock stress were analyzed respectively,and the settlement deformation was summarized.The law determines the position of maximum settlement,and analyzes the law and scope of the influence of ground fissures on the tunnel.The results show that the influence of ground fissures on tunnel excavation is greater on the hanging wall than on the footwall,and the settlement value of the hanging wall is greater than that of the footwall.(3)Through the optimization of the initial support to reduce the impact on the surface settlement of the tunnel crossing the ground fissure,on the premise of using CRD method to excavate,the numerical models of the original initial support and the optimized initial support are established and compared,and the optimized initial support scheme is obtained.By optimizing the construction method to control the ground settlement,the numerical models of the double-side pilot method and the optimized CRD method were established to compare and analyze with the original CRD method,and the optimized construction plan was obtained.The results show that,in terms of controlling surface settlement,the double-side-wall pilot method has the best effect,the optimized CRD method is the second,and the optimized initial support scheme has the least effect.(4)Based on the monitoring and measurement data of the whole construction process,the change law of surface settlement and vault settlement was analyzed,and the monitoring data and simulation data were compared to verify the rationality of the determined construction scheme.Establish a three-dimensional visualization model of the tunnel,and design a monitoring data analysis and early warning system based on the secondary development function of Revit to realize dynamic monitoring of tunnel construction. |
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