Fluid-solid Coupling Analysis Of The Disaster-causing Mechanism Of Municipal Pipeline Burst Outside Foundation Pit

With the development of society and urban construction,people have increased the exploitation and utilization of underground space.Foundation pit engineering,as a basic stage,has been paid more and more attention to its safety and reliability.However,due to the complexity,uncertainty,and various human factors of foundation pit engineering,accidents occur from time to time.Studying the mechanism of the accident can provide a reference for future engineering design and construction.This article takes the safety accident of the side wall of the foundation pit caused by a municipal pipeline bursting outside the foundation pit as an engineering case,and the collapse of a foundation pit in Nanning as an engineering case.Based on the theory of seepage,consolidation and fluid-solid coupling,COMSOL Multiphysics software is used to study the mechanism of the pit sidewall failure caused by pipeline burst in this paper.The working state of the foundation pit before and after the water burst of the municipal pipeline at the top of the pit is studied,and the influence of the top anchor cable failure on foundation pit deformation is analyzed.Finally,thispaper discussed the reliability and limitation of the simulation results.The results show that:(1)The bursting of the municipal pipeline outside the foundation pit will cause the soil and water pressure in the surrounding soil layer with good permeability to be greatly increased,which will easily cause the surface layer of the foundation pit sidewall to be damaged,and also increase the lateral pressure of the supporting pile.However,when the strength of the pile body and the embedded conditions(including the bottom of the pile and the anchor cable)are normal,the deformation is not large.(2)When the anchor cable at the top of the pile fails,the lateral deformation of the pile body increases,the foundation soil on the side of the pile is displaced in the direction of the foundation pit,and the surrounding ground settlement increases.The axial force of anchor cable under pile top also changes,and the axial force of the second anchor cable increases significantly.(3)In the early stage of foundation pit lateral wall instability caused by the burst of municipal pipelines outside the foundation pit,the anchoring force was gradually weakened due to water infiltration to the anchoring section of anchor cable at the top of the pile,which shows that the deformation of foundation pit supporting structure develops slowly.In the later stage,the failure of pile top anchor cable,the development of plasticzone in the soil body outside the foundation pit and the occurrence of continuous sliding surface show that the deformation of the foundation pit support structure increases rapidly until it triggers a chain reaction,which leads to the collapse of the foundation pit side wall.(4)The analysis conclusions of multi-field coupled numerical simulation in pipeline damage prediction,the main area affected by the burst of water and foundation pit collapse sliding surface are basically consistent with the actual situation of the project,and the mechanism of the collapse of the side wall of the foundation pit caused by the burst of the municipal pipeline is well revealed.(5)In view of the actual technical level,this research has simplified the actual engineering to a certain extent.The numerical simulation analysis results still differ from the actual engineering situation,and further work needs to be carried out in the field of multi-field coupling experiments and theoretical research.The research results of this paper have a good engineering guidance for the design and construction of the foundation pit of adjacent municipal pipelines,and also play an important role in promoting the application of multi-field coupled numerical analysis method to the study of complex engineering problems under combined effect of multiple factors.