Study On Mechanical Properties Of Horseshoe Segmented Tunnel Crossing Ground Cracks In Different Ways

As the only national central city in northwest China,Xi’an has developed rapidly in recent years.In order to alleviate congestion,it is vigorously developing urban rail transit construction.Currently,more than ten ground fissures have been discovered in Xi’an,and they are bound to cross the ground fissure zone during construction,resulting in the impact of ground fissures on the tunnel lining.This paper takes the Xi’an Metro construction project as the engineering background,takes the tunnel crossing the ground fissure site as the research object,and combines the model tests carried out by the research group.Based on the comparison of physical model tests and finite element simulation tests,through numerical simulation tests,a model is established for two crossing angles and eight working conditions,focusing on the interaction between the ground fissure and different locations of the tunnel.The main research work and achievements are as follows:(1)The mechanical properties of subway tunnels crossing ground cracks at 90 and 60 degrees are studied.According to the analysis of the experimental results,it is concluded that the bottom of the upper plate tunnel will have a certain range of voids and the void depth and width will change in opposite directions,and most of them are located at the places crossing the neutral and ground cracks.(2)When the angle of section tunnel crossing ground fissure is 90 degrees,its mechanical properties are analyzed by numerical simulation test.It can be concluded that the deformation is mainly bending deformation and the stress is symmetrical.(3)The calculation model of sectional tunnel is selected,and the mechanical properties of sectional tunnel with length of 10 m under 90 degrees orthogonal condition and settlement of 0.5m are calculated and analyzed.The bending moment and shear force of sectional tunnel under different conditions is obtained,and the finite element test results are compared and verified.(4)When the angle of section tunnel crossing the ground crack is 60 degrees,the mechanical properties of the tunnel are analyzed by numerical simulation test.It can be seen that the stress of the tunnel is obviously asymmetric,not only subject to bending deformation,but also to certain torsional deformation.(5)When the upper plate gradually decreases,under the action of earth pressure,the tunnel section will appear obvious side drum phenomenon,especially when the tunnel crosses the ground fissure at 60 degrees obliquely.