Analysis On The Application Of Composite Soil Nailing Wall In Foundation Pit Of Secondary Slope

With the soaring development of social-economic,a large number of people have flooded into the city,more and more high-rise buildings,rail transportation network extending in all directions,a variety of related supporting facilities have been planted everywhere,resulting in a large number of foundation pit excavation projects.The densely packed surrounding environment of the foundation pit,complicated geological conditions and high construction difficulty are problems that placed in the foundation pit project.Selecting the appropriate foundation pit support structure in conjunction with relevant factors is the key to solving the problem.Composite soil nailing wall is a kind of supporting structure which is an active control mechanism between rigid and flexible supports.It has the advantages of convenient construction,little disturbance to the surrounding environment,and strong stability of the foundation pit.Taking into account factors such as economic performance and surrounding building environment safety,the secondary grading foundation pit combines the stability of its own soil with the composite soil-nailed wall structure,which is an advantage of local conditions and other support structures that do not possess.It is worthy of promotion and extensive application in foundation pit engineering.This paper is based on the Yongsheng home project of the second phase of Baisha resettlement area,and the combination of a two-level sloping foundation pit and a micro-pillar pre-stressed anchor composite soil nailing wall support structure.Using the finite element analysis software ABAQUS,a model was established according to the actual excavation and support sequence of the foundation pit.The stress characteristics and deformation characteristics of the composite soil-nailed wall supporting structure on the secondary grading excavation pit were studied.The pit and support methods provide a reference.The main research contents and conclusions of this paper are as follows:(1)The previous achievements in theory,experiment and simulation of composite soil nailing wall,the stability checking of composite soil nailing wall and the mechanism of action of each component are introduced.(2)The finite element ABAQUS software was used to simulate and analyze the stress characteristics of support members and the deformation of the composite soil nail wall.Through the horizontal comparison analysis,the maximum horizontal displacement of the second grade sloping foundation pit compared with the grading foundation pit was reduced by 43%.The slope-retreating platform,prestressed anchors,and micro-piles have an important role in improving the deformation of the second-grade retreat foundation pit,the stress of supporting members,and enhancing the stability of the foundation pit(3)With the increase of the width of the secondary grading,the maximum horizontal displacement of the foundation pit and the axial force of the supporting member could be reduced effectively,and the stability of the foundation pit can be enhanced.With the increase in the width of the retreat,the constraints on the displacement of the foundation pit have also weakened.(4)The prestressed anchor bolts have an significant influence on the axial force of the adjacent upper soil nailing structure and the next row of soil nailing structures,and the impact of the bolt on the upper soil nailing structure is more obvious than the lower one.The effect of anchor bolts on the horizontal displacement of the foundation pit is greater than that of soil nails of the same length.