Numerical Simulation Of Composite Soil Nailing And Pile Anchor Retaining Structure For Deep Foundation Pit In Loess Area

With more and more deep foundation pit projects in loess area,the deep foundation pit engineering is becoming more and more complex,and the consequent requirements for safety and economy of the deep foundation pit supporting structure in loess area are becoming higher and higher.Because of the particularity of loess,the design and construction of deep foundation pit supporting in loess area is different from other areas,which further increases the difficulty of deep foundation pit support engineering.The composite soil nailing pile and anchor retaining structure has become a kind of widely used supporting form in deep foundation pit engineering in Loess area because of its strong applicability,safety,economy and so on in the loess area.However,in application,there are still many problems due to the imperfect theory.Such as the waste caused by excessive security reserve in design and construction process,security risks caused by the use of unsuitable conditions.This paper is based on a deep foundation pit engineering of composite soil nailing and pile anchor retaining structure in Taiyuan,and the finite element analysis software Plaxis is used to simulate the stress and displacement.Thefactors that affect the displacement of the project are analyzed,and the influence of different soil water content on the supporting structure is studied.So as to provide suggestions and references for the similar engineering of composite soil nailing and pile anchor retaining structure in practice.Through the above research and analysis,the following conclusions are drawn:1>Horizontal displacement of foundation pit is mainly related to earth excavation,and the deeper the excavation face,the greater the excavating depth,the greater the lateral displacement.The largest part of the displacement of the composite soil nailing and pile anchor retaining structure is located in the middle and lower part of the supporting pile,control displacement shall be taken from this position.2>In the vicinity of the supporting structure,Basement uplift is small,with the increase of the distance to the supporting structure,it tends to be stable.The uplift of the basement is related to the excavation depth,the larger the excavation soil,the larger the basement uplift.3>In the supporting structure,the maximum tensile force of soil nails and prestressed anchors is near the supporting structure,to the end gradually reduced to zero.The anchor rod bears the tension and the soil nail is used to reinforce the soil,they take a combined action to control the horizontal displacement.4>It is not recommended to increase the rigidity of the retaining pile to control the displacement.Increasing the anchorage section of the prestressedanchor rod can reduce the lateral displacement of the supporting structure,but the effect is not obvious when the length is too long.So we should choose the appropriate length of anchorage section according to the specific circumstances of the project.5>The smaller the soil water content(or saturation)is,the greater the shear strength is,which is beneficial to the project,but the increase of water content will reduce the shear strength of the loess.It is indicated that the unsaturated soil properties of loess are beneficial to the engineering in the loess area,but the adverse effects of the water content variation on the project should also be considered.