Study Of Soil Settlement Law Induced By Excavation Disturbance And Rainfall Infiltration

In recent years,the scale and quantity of underground engineering construction have shown a surge trend,which is affected by many disturbance,near excavation,heavy rainfall immersion and groundwater level change.Underground hidden diseases(loose,water damage,cavity)induce construction disasters and accidents frequently,resulting in serious social and economic losses.Underground excavation disturbs the original soil stress field,breaks the original equilibrium state,causes surface subsidence and horizontal movement,and causes disastrous damage to stratigraphic environment and surrounding buildings.Rainfall will not only change the physical and mechanical parameters of soil,make the water content and pore pressure of soil surface change obviously,but also change the seepage field and stress field of soil,and then easily lead to collapse,landslide and other disasters.It is of great significance to study the settlement of soil caused by foundation pit excavation to prevent surface settlement deformation and construction safety.Accordingly,this paper focuses on the influence of excavation and rainfall on the ettlement law of soil around foundation pit.Taking a foundation pit project of Shangcheng Avenue Tunnel Project in Yiwu City as an example,The numerical experimental study of soil settlement and deformation affected by excavation disturbance and rainfall is carried out by using the Universal Distinct Element Code(UDEC).(1)This paper comprehensively analyzes the research status of the law of ground subsidence at home and abroad,as well as the collapse accidents in foundation pit engineering in China in recent years and several common measures to control subsidence,and draws out the research purpose,content and technical route of this paper.(2)Introducing practical engineering cases,introducing the basic principle of discrete element method and joint seepage model,establishing numerical model,analyzing the main causes of soil settlement during excavation by changing rainfall intensity and excavation depth,and analyzing the data of displacement and pore pressure of monitoring points,it is shown that the depth of excavation will have a certain influence on the pore water pressure,horizontal displacement and settlement of soil layer.With the increase of excavation depth,the pore water pressure will decrease,while the settlement of soil layer will increase obviously,and the farther away from the excavation site,the smaller the influence of pore water pressure and settlement will be.For the same excavation depth,the influence of rainfall intensity on the settlement of soil layer is not very great,and it is easy to be affected by excavation conditions.The soil near the upper layer of soil is prone to settlement after excavation,and the variation law of settlement is similar,while the lower layer of soil is relatively small.The upper soil is easy to be affected by excavation,the horizontal displacement is large,the change trend of horizontal displacement in the same soil layer is similar,and the horizontal displacement value decreases gradually with the increase of excavation depth.(3)By using the number of joints in the UDEC,the ratio of the spacing between the joints and the spacing between the joints,the degree of fragmentation of the soil affected by the pipeline,the hidden diseases and the distribution of voids or defects in the soil layer are characterized.The higher the degree of soil dispersion and the density of voids or defects in the soil layer will aggravate the settlement of the surrounding soil,which may lead to a large range of soil collapse and induce engineering disasters.(4)By analyzing the displacement of monitoring points of the undisturbed soil,the settlement and deformation law of the soil in the near field caused by the disturbance of rainfall infiltration and excavation were obtained.The results show that the influence of rainfall intensity on the settlement of the upper soil is great when the excavation depth is constant,and the influence decreases with the increase of the depth.The settlement and horizontal displacement of the monitoring point is affected by the distance between the monitoring point and the excavation area.The closer the soil layer is to the excavation area,the greater the settlement and horizontal displacement,the more stable the lower soil is,and the minimum horizontal displacement is.By comparing the experimental data with the simulated data,it is found that the finer the joint spacing of the model is,the better it can reflect the defects,voids and other diseases in the soil,which further verifies the feasibility of the simulation and provides a safety basis for the engineering construction.