Research On The Application Of Step-slope And Cement Mixing Pile Reinforced In Deep Soft Soil Foundation Pits

The deep quaternary soft soil is widely distributed in Pearl River Delta.For deep foundation pit in soft soil area,the support system of cast-in-place pile and SMW construction pile combined with internal support or multi-channel anchor cable is often adopted.However,if such support scheme is continued for the foundation pit with single-layer basement and excavation depth of 4-6m,the economy and efficiency will be lower.For this kind of foundation pit,cement mixing pile is used to reinforce the slope of the foundation pit and the passive area in the pit when there are certain site conditions and slope excavation is not enough to meet the stability requirements of the foundation pit.However,this practice precedes the theory.At present,there are few researches on the influence of cement mixing pile on the deformation and stability of this kind of foundation pit,and the setting of safety coefficient calculated based on the limit equilibrium method of positive correction software also fails to reflect the real situation.Therefore,the finite element method is adopted in this paper to study the reinforcement of deep soft soil,especially the slope setting and cement mixing pile in the foundation pit in the silt area.Based on the relevant research status,the main contents of this paper are as follows:(1)Consult literature to understand the research theory and engineering application of the supporting structure of cement mixing pile,and summarize the characteristics of soft soil,the supporting form of soft soil foundation pit and the research status at home and abroad;(2)Summarized the earth pressure model and the analysis method of the internal force of the cement mixing pile,summarized the checking formulas of the overall stability,anti-overturning and anti-sliding to determine the design size of the slope cement mixing pile;The mechanical properties and engineering applications of cement-soil materials are summarized,and the arrangement forms and applicable conditions are discussed.(3)A three-dimensional numerical model was established based on a deep soft soil foundation pit strengthened by a slope and cement mixing pile in nansha,guangzhou.The calculated values of the horizontal displacement and settlement of the foundation pit in the unreinforced foundation pit and the reinforcement scheme at different construction stages were analyzed and compared with the on-site monitoring values to verify the rationality of the model.(4)Using finite element method to establish a calculation model of slope setting combined with cement mixing pile reinforcement.Firstly,verify the thickness of the model,and then analyze the influence of construction conditions,the layout position,width,row number and embedded depth of the single row cement mixing pile wall on the foundation pit deformation and overall stability.Finally,the influence of the depth and width of the cement mixing pile wall on the deformation and overall stability of the foundation pit in the passive area of the pit is analyzed,and the reinforcement effect under different reinforcement volumes in the passive area of the pit is compared.Through the research and verification,the conclusion is drawn that the effect of slope setting and cement mixing pile reinforcement on the foundation pit deformation and its stability in deep silt area is worthy of affirmation,which has certain reference significance for similar projects.