Study On The Arch-cap Structure's Cracking Of The Subway Station And The Reason Analyze

With the increasingly saturated of ground buildings and traffic space,the development and utilization of urban underground space has been appreciated.As the underground public transport project,urban subway has made a great contribution to alleviate and solve the traffic pressure to the ground.More than 150 years of development,The record of the section has continuously updated of the subway station,among which,the big arch is a new type of subway station.The environment of the underground engineering is relatively closed,complex geological and high stress over a long time.Any little uncertainty change can have a great influence on stress of the structure,which cause the structure's cracking.In this paper,based on the theory of fracture mechanics,in combination with the method of XFEM in ABAQUS,analysis the extention,damage location and the shape of cracking on the arch structure of the subway station with in different local bias load,uneven settlement,the changing of coefficient of lateral pressure and the thickness of arch structure.(1)The model test of tunnel lining in Japan is compared with the numerical simulation results,it is concluded that the simulation results are consistent with the crack position of the model test.The feasibility and applicability of XFEM method to simulate the cracking of lining structure are demonstrated.It provides a theoretical basis for simulating the crack of arch arch.(2)When the bias is applied to the structure,The cracks and failure modes of the arch structure are inconsistent with the variation of the bias range.With the increase of range,the structure is more prone to crack;When the structure starts to crack,the surface corresponded to the bias is splay by the bending moment;The circumferential displacement of the structure above the crack surface is greater than that of the lower part;The crack propagation rate under the same load increases with the increase of the partial pressure range.When the partial pressure range is small,the lateral structural concrete is crushed as the load increases;when the bias range is relatively large,it is mainly caused by the penetration of the main crack and the crushing of the concrete.Meanwhile,the upper and lower surfaces of the bias range and the outer surface of the left arch foot will produce the crack zone.Under the impact of partial bias,the crack propagation length increases with the increase of the longitudinal bias length,and shows the phenomenon that the two ends are slightly bent to the top of arch in the spatial form.(3)When the arch structure produces lateral uneven settlement,the structure first produces a tension crack on the outer surface of the left arch,and as the settlement volume increases,the crack gradually penetrates,showing the shear crack,at the same time,the outer surface of the left and right arch foot and the inner surface of the arch surface produce the crack zone,and the crack range of the right arch is larger than that of the left arch.When the arch structure produces longitudinal uneven settlement,at first,outside surface of the vault symmetrical produce two crack,with the increase of sedimentation value,arch bottom appear vertical cracks and expand at close to 45° in settlement place,the main crack extension accelerated gradually,to the subsidence of break,in settlement place show that the tension crack,the other end of the show the shear crack.(4)Different lateral pressure coefficients combining cavity exists in arch structure: when the holes in the dome area,with the increase of the lateral pressure coefficient,the hole surface of arch first made a mouth of the bending crack.when the structure getting damage,vault hollow area,left and right sides of the inner surface of arch hance and arch foot outside surface produce the crack zone;When the hole is located in hance,this area concrete will first be extrusion deformation,with the increase of the lateral pressure coefficient,and produce "V" shape of the bending crack mouth.Along with the coefficient of lateral pressure continues to increase,the hole area outside surface,the inner surface of the left arch,the outer surface of the left arch and the inner surface of the right arch will produce the crack zone.(5)With the increase of the thickness of the arch structure,the crack load gradually increases and the crack propagation speed gradually decreases.(6)The numerical simulation of cracks is classified into three types with morphology and position: Firstly,under the action of bias and different lateral pressure coefficients,the arch-cap structure is first produced under the bending crack.The more of that is the longitudinal crack,with the increase of load in the ring to expand rapidly;Secondly,the longitudinal non-uniform sedimentation mainly produces oblique and circular cracks,the crack in the subsidence area is mainly of the bending crack,with the increase of the settlement value,there will be a shear failure on the other side;Thirdly,the transverse uneven settlement at first occurs a curved crack at the arch position,with the increase of settlement value,shear failure occurs,resulting in a shear crack.(7)To summary and describe the corresponding relationship between the disease and crack,it is concluded that the inner surface of the hance and the outer surface of the arch foot are the areas where the crack of the arch structure is relatively easy to produce.The corresponding table of crack location and disease is obtained,which provides reference for the production and judgment of cracks in actual engineering.