Research On Soil Nail Bracing Performance Of Foundation Pit Based On Midas/GTS FEM Analysis

Because of simple,rapid,economic and other unique advantages,Soil nailing support technology is widely used in deep foundation pit engineering,but its design theory lags far behind engineering practice,especially lack of practical calculation method when calculating the displacement of soil nailing support structure and empirical design method play an important role in the foundation pit support.There are many examples of engineering projects due to failure of soil nails that caused damage to deep foundation pits or major accidents at domestic and foreign.On the basis of summarizing the achievements of previous researches,this paper takes deep foundation pit project of the Crystal · Kabala Southern Area as an example,combines the in-situ monitoring data of the foundation pit,the elastic modulus of soil were calibrated and checked.Based on the FEM analysis,the work performance of soil nailing support structure have been further studied and compared with the pile-anchor support structure,and some research results have been obtained,expecting to provide help for the research and application of design,construction and in-situ monitoring of soil nailing structures.The main work of this paper is as follows:1.The concept and characteristics of soil nailing support,the research status of soil nailing technology both at domestic and foreign were systematically summarized through the collation and analysis of references,the action mechanism and the design theory of soil nailing wall were summed up;The soil nailing support on the south slope of Crystal · Kabala Southern Area foundation pit was designed by F-SPW software.2.Based on the design drawings of the foundation pit,a three-dimensional finite element model of the soil nailing wall on the south slope of the foundation pit was established by Midas/GTS finite element software.Combined with the in-situ monitoring of the foundation pit,the elastic modulus of the soil within the depth of the foundation pit were calibrated,and then the characteristics of soil displacement,stress and the axial force of the soil nail with the step excavation process of the foundation pit,were analyzed through simulation analysis of the construction process of soil nailing.3.Through the comparison of the simulation results of the pile anchor support on the west slope of the foundation pit and the in-situ monitoring data,firstly the calibration results of the soil elastic modulus was checked,and then compared with the soil nailing wall with the same overload on the south slope.The advantages and disadvantages of soil nailing wall were analyzed in several aspects including soil deformation,slope stress,supporting structure force and slope stability.The research and analysis show that in the numerical simulation,the actual situation of excavation and support of the foundation pit can be better reflected after the soil elastic modulus calibration.When the elastic modulus is large,the impact of the elastic model changes on the soil displacement is small;The frequency of pit in-situ monitoring should be appropriately increased with the excavation depth;compared with pile-anchor support,the deformation of soil nailing wall is significantly increased,the stress concentration of soil is reduced,the force of supporting structures is significantly reduced,and the axial force of soil nails in the middle of the wall is the largest,and the slope stability coefficient decreases by approximately 13.2%.