Study On Ground Deformation And Its Influence Induced By Weakening Of Unsaturated Soil Caused By Pipeline Leakage

At present,major cities are generally faced with the problem of land subsidence deformation and collapse.As the main factors inducing urban ground deformation and collapse,more and more attention has been paid to the soil deformation induced by weakening of unsaturated soil caused by pipeline leakage and its influence on the safety of existing buildings around the pipeline.In this paper,based on the finite element numerical simulation method.First of all,the law of water seepage and diffusion in the soil layer after pipeline leakage is analyzed.Secondly,considering the change rule of soil shear strength index with soil moisture content,the finite element subroutine is secondly developed to realize the water softening effect of the soil.Finally,the soil deformation induced by weakening of unsaturated soil caused by pipeline leakage and its influence on the safety of existing buildings around the pipeline are analyzed.The main research results are as follows:(1)The law of water body diffusion in the soil is that the water body gradually diffuses out from the leakage port under the action of the leakage pressure,and different time-space effects are generated by different influencing factors.For example,different leakage locations and different buried depths show spatial effects;different leakage pressures and different soil permeability characteristics show time effects.(2)Through the secondary development of the USDFLD subroutine of finite element software ABAQUS,the effect of soil water softening is realized,and the soil strength index is changed according to the specific strength formula.The friction angle is linearly changed with saturation and the cohesive varies exponentially with saturation.(3)The effect of soil softening on soil deformation is:under the condition of no load,the degree of soil softening is limited and water infiltration will cause a certain degree of uplift on the surface;under the action of surface load,the softening effect of soil the degree is obvious.With the development of leakage,the plastic zone in the soil continues to increase.(4)The uneven settlement difference of buildings caused by softening of soil shows an exponential change with the leakage time.At the same time,it can be seen that the pile foundation has better ability to resist settlement.Without external disturbance,the pile foundation is safer when the pipeline leaks.In the same situation,there is a high probability that the shallow foundation will be dangerous.The paper believes that it is safer to keep the distance between the building and the pipeline 20m in order to prevent pipeline leakage from causing serious damage to shallow foundation buildings.(5)In the influence of softening soil on buildings,the degree of influence of different influencing factors is:The distance from the different buildings of the pipeline>the length of the pile(shallow foundation depth)>the degree of influence of the pipeline depth.The settlement difference of the building varies exponentially with the distance from the building to the pipeline,and varies linearly with the length of the pile(shallow foundation depth),while the buried depth of the pipeline shows only a certain impact in the early stage of leakage.The research results of this paper are helpful to analyze and understand the impact of urban pipeline leakage on unsaturated soil layers and surrounding environment,and is of great significance to the understanding and research of urban ground subsidence deformation and settlement deformation of buildings.