Research On The Structural Behaviors Of Urban Underground Pipe Gallery In Active Ground Fissures Environment

Urban underground pipe gallery is an important part of the construction of"sponge city",which can greatly improve the utilization rate of urban underground space,promote the sustainable development of the city,and is an important"lifeline system"of the city.As the starting point city of"the Belt and Road"and cosmopolitan city,the construction of underground pipe gallery has entered a rapid development stage in Xi’an city.However,the development of ground fissure has brought serious security risks to the construction of underground pipe gallery in Xi’an city.What more serious is that the ground fissure disaster may lead to the cracking and destruction of underground structures,and then lead to secondary disasters,which seriously threatens the safety of life and property for urban residents.This paper takes the background of Kunming Road’s underground pipe gallery crossing through ground fissure zone as research object.Based on field survey,the activity characteristics of ground fissures in the proposed site was clarified,and the deformation and mechanical behaviors of urban underground pipeline gallery under the action of active ground fissure were studied by large-scale finite element simulation calculation and theoretical analytic method systematically,then the influence mechanism of ground fissure dislocation on the pipe gallery was revealed,and relevant prevention and control countermeasures were put forward and which can provide scientific reference for the construction of underground pipeline gallery in ground fissures development areas.The main research results are as follows:（1）Based on the activity characteristics of ground fissures in Xi’an and analysis of genetic mechanism,the active characteristics of ground fissures along the Kunming road underground pipe gallery was clarified and future activity of ground fissures was analyzed and the maximum dislocation quantity of ground fissures in the design term of the pipe gallery was determined.（2）The three-dimensional geomechanical model with the different intersections（30°、60°and 90°）of underground pipe gallery with the ground fissures was built with the Midas/GTS,the deformation and stress characteristics of the underground composite pipe gallery and stratum in the cross-ground fracture zone were studied,the influence range of the composite pipe gallery caused by the dislocation of the ground fissure was determined,and the deformation and failure mechanism of the underground pipe gallery under the action of the dislocation of the ground fissure was revealed.（3）Based on structural mechanics theory,the pipe gallery-adjacent rock stratum calculation model with ground fissure dislocation was established,the cross-sectional internal force of pipe gallery crossing ground fissure zone was studied and the corresponding internal force calculation formula was deduced and the rationality of the formula was verified by calculation an example.（4）Based on the elastic foundation beam theory,the pipe gallery-adjacent rock stratum longitudinal deformation and mechanics calculation model was established,in which pipe gallery could be divided into two sections:anchorage section and loading section,and the internal forces of each section of pipe gallery structure could be solved respectively.At the same time,the bending moment values of structures with different anchorage lengths（l₂=10m、12m、14m、16m and18m）was analyzed,and the optimum length of underground pipe gallery across ground fissure zone as l₂=14m of anchorage section was determined.The rationality of the formulas was verified by means of inverse displacement calculation.（5）Based on the analysis of the influence of ground fissure dislocation on the pipe gallery,the external structure of the pipeline gallery which can adopt segmental joints,flexible joints and other auxiliary measures was proposed.Based on the finite element numerical simulation calculation,the rationality of the prevention and control measures was analyzed.Some fortification countermeasures to ensure the safety of pipeline access,such as installing adjustable supports and setting up monitoring and early warning of pipeline deformation were put forward so as to provide reference for the construction of underground pipeline gallery in the ground fissure development areas.