Study On The Application Of Prestressed Anchor Composite Soil Nailing Wall In Deep Foundation Pit

Firstly,this paper describes the functioning characteristics of soil nailing wall retaining structure and the functioning characteristics of each unit in it.Then the composite soil nailing retaining structure is introduced.The calculation method of slope stability under composite soil nailing with prestressed anchor rod is expounded.Meanwhile,the functioning characteristics of each member in the prestressed bolt retaining structure is illustrated.Through the theoretical analysis of the functioning characteristics of soil nailing and prestressed anchor,a suitable numerical calculation software and a reasonable type of structural unit(shell?cable?beam)are selected to simulate and calculate for a retaining section in construction site.At the same time,two sections of the construction site are selected as the test object,and the field test scheme is made and tested.In the field test,the displacement at the top,bottom and middle of slope are monitored in the foundation pit in real time.The displacement curves are plotted according to the result monitored,and the stress of anchor and soil nail in each construction stage is monitored.For the field test,the horizontal displacement of slope and the vertical displacement of monitoring point at the top of the foundation pit are monitored in real time.After analyzing and processing the data,the horizontal displacement curves in each construction stage and the settlement curves of the top foundation pit are plotted.Through the above research,the following conclusions are made in order to provide reference for the design and construction of similar foundation pit engineering in Lanzhou area.The main work and achievements of this paper are as follows:(1)The development and application of soil nailing wall retaining structure are described.The retaining theory of soil nail wall is the same as the new Austrian Law.The original soil strength can be made full use of,meanwhile the corresponding retaining structure is applied so that the soil in the affected digging area can be stabilized quickly.Soil nail wall retaining structure has the advantages of fast construction speed,low cost and low technical difficulty.When the surrounding environment permits,it is the second choice except for slope excavation.(2)Not only the composite soil nailing structure has the advantage of low cost,fast construction speed and low technical difficulty,but also it can effectively control the displacement of the slope.However,it occupies the underground space around the foundation pit too much.The functioning principle of each member of the composite retaining structure combining prestressed anchor and soil nail wall,and the stress distribution of the anchor and soil nail are concluded and discussed.Besides,the slope stability analysis method retained by this kind of composite soil nailing wall is analyzed and studied.(3)The finite difference calculation software is used to calculate a construction section.The results show that the displacement is relatively small at the interface between hard rock and soft soil.The maximum displacement of the soft soil appears in the middle.There is a difference between the numerical calculation results for the vertical displacement of the slope and the actual monitoring results of other projects,which is related to the incomplete constitutive relation of soil materials.The axial force of the soil nail and the anchor rod is higher in middle,and lower at two ends,which distributes like a date core.With the increase of excavation depth of foundation pit,the uplift of soil at the center bottom of foundation pit shows an increasing trend.However,after the completion of the same stage of excavation,the uplift of the pit increases first then developed steadily from the slope toe to the center.(4)Two sections,which can satisfy this study,whose geological conditions are basically same,are chosen to be monitored.The horizontal displacement of slope and vertical displacement of a point at the top foundation pit are monitored.The results show that the maximum horizontal displacement of the section retained by two prestressed anchor rods is about half of the maximum displacement of the section retained by one.The top settlement can be controlled effectively by using the soil nailing wall supported by two anchor rods.