| Ground fissures are a special geological disaster in Xi'an.A total of 14 structural fissures are spread,which has a serious impact on urban construction and people's production and life.With the urbanization process and the construction of the subway network,subway tunnels will inevitably be affected by ground fissure field activities.It is of great engineering application value to carry out stress analysis and disaster prevention of Xi'an subway tunnel structures under ground fissure activities.Based on a subway tunnel in Xi'an,this paper studies the deformation and failure mechanism and disaster prevention of subway tunnel structure under the action of ground fissures.The main work and conclusions are:(1)Using FLAC3D large-scale finite element software to simulate the deformation of subway tunnel structure under the action of ground fissures.Taking no ground crack and ground crack with a distance of 50m as the research object,the existence of ground crack has little influence on the change of the plastic zone of the surrounding rock caused by the tunnel excavation,but has no influence on the deformation of the surrounding rock of the tunnel Fourworking conditions of joint movement and parallel tunnel,i.e.10m,30m and 50m,are studied.The dislocation of ground crack has a larger disturbance distance to footwall.The smaller the parallel distance between ground crack and subway tunnel is,the larger the vertical maximum deformation is,and the larger the magnification factor is.With the decrease of parallel distance,the faster the vertical maximum deformation and magnification factor increase;with no ground crack,ground crack and tunnel The intersection angle is 60°,75° and 90° as the research object.The staggered movement of the ground crack causes the plastic zone of the side wall of the arch waist and the arch bottom to increase gradually.The smaller the intersection angle is,the larger the maximum deformation and the amplification coefficient are,and the faster the growth rate is,and the intersection condition is greater than the amplification effect of the parallel condition.(2)According to the study on the calculation of surrounding rock pressure,load combination mode and stress characteristics of tunnel lining structure under the action of ground fissure,the vertical and lateral uniformly distributed load values of surrounding rock obtained by the tunnel excavation method are greater than those obtained by the buried pipe earth pressure method.In the process of calculating the surrounding rock pressure of the subway line section with ground cracks,the friction force of the surrounding rock mass on both sides of the tunnel due to the downward settlement of the surrounding rock mass on the top of the tunnel and the tunnel lining structure should be considered,and the surrounding rock pressure of the tunnel lining across the ground cracks is far greater than the surrounding rock pressure of the metro tunnel in general.The internal force value of each node of the tunnel lining structure is calculated by the elastic support method.Because the surrounding rock on both sides of the tunnel at the ground crack has a downward movement trend,the downward force on the tunnel lining structure and the top surrounding rock makes the maximum bending moment of the lining structure occur at the vault position,and the arch waist position is in the tension state.(3)Carry out safety evaluation on subway tunnel engineering disasters under ground fissure activities,analyze and summarize the disaster characteristics and types of subway engineering disasters under ground fissure activities,and propose that both "prevention" and"control" should be adopted when subway tunnels cross ground fissure sites Combining the principles,the preventive countermeasures for subway tunnel lining structure under ground fissure activities are proposed from three aspects:structural preventive measures,safety early warning measures,and other preventive measures.At the same time,measures for post-disaster control are proposed to reduce or eliminate the ground fissure activities Possible disaster. |
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