Deformation Law And Control Technology Of Adjacent Underground Pipelines Induced By Excavation Of Metro Tunnel Crossing Ground Fissure

Ground fissures are a unique type of geological problem encountered during the construction of Xi'an Metro.In recent years,it has attracted great attention from the engineering and academic circles.How to ensure the safety of underground pipelines along the subway during the excavation process of the subway tunnel crossing,the ground fissure and its operation period has become an important issue to be solved in urban subway engneering.Therefore,it is of great theoretical significance and engineering application value to carry out the research on the influence law of underground excavated subway tunnel through ground fissure on the deformation of adjacent underground pipelines.This paper takes the Tong-Hu section tunnel of Xi'an Metro Line 3 as the research background,and uses the method of field investigation,theoretical analysis and numerical simulation to carry out research work.The main work and conclusions are as follows:(1)The on-site investigation method was used to investigate the distribution or pipelines near the Xi'an subway line,and the classification methods and failure modes of underground pipelines were summarized.The failure reasons of the pipelines were obtained through the force analysis,the longitudinal stress and the hoop stress affected the pipeline deformation mostly.At the sane time,the pipeline deformation control standard is proposed and the pipeline protection measures are given.(2)The distribution characteristics,structural characteristics,activity characteristics and hazards of ground fissures in Xi'an area are described,the stress characteristics of the soil around the ground fissures are analyzed.Research shows that the speed of settlement at the top of the tunneling face occurs very quickly,while the speed away from the settlement surface becomes slowly,and the range of lateral deformation is closely related to the diameter of the subway tunnel,generally,the lateral deformation occurs within the range of 2or 3 times the tunnel diameter.(3)Based on the shear-slip theory,the effect of ground fissures is simplified to external loads,and the pipeline model is simplified to cantilever beams or statically indeterminate beams,also based on the Winkler elastic foundation beam theory,the theoretical prediction formula of underground pipeline deformation induced by underground excavation of ground fissure subway tunnels is deduced when the pipeline and the subway tunnel will cross perpendicularly and parallel;research shows that the formula prediction results are basically consistent with the numerical simulation results.The pipeline deformation control technology when the subway tunnel crosses the ground fissure is proposed.(4)Based on Flac3D numerical simulation,the law of deformation of adjacent underground pipelines induced by underground excavation of subway tunnels crossing ground fissures is obtained.The research results show that:the long-term development of ground fissures has a greater impact on the deformation of the pipeline,the deformation rate of the pipeline accelerates with the change of time;whether the pipeline is perpendicular or parallel to the subway tunnel,the position where the pipeline crosses the ground fissure has the largest deformation;Under the simultaneous influence of the development of ground fissure and the construction of subway tunnel,the deformation curve of the pipeline is basically the same as the subway tunnel construction alone,but the maximum deformation is approximately doubled;when the pipeline crosses the ground fissure at a small angle,the displacement of the ground fissure will have a great impact of the pipeline's deformation.