Calculation Of Internal Force And Displacement Of Soil Nailing Wall Based On Limit Equilibrium Analysis

With the development of urbanization in China,the demand for urban land is increasing,which leads to the increasing number and scale of foundation pit engineering.As a representative flexible support structure,soil nailing wall is widely used in foundation pit,slope and mining engineering.It has the advantages of low cost,fast construction speed and wide application.However,for the soil slope with small slope,the reduced Rankine earth pressure is generally used to calculate the internal force of the soil nailing support structure,and the earth pressure is allocated to the soil nailing according to the distribution form of Rankine earth pressure,while the distribution law of soil pressure on the soil slope with small slope is ignored.At present,the theoretical calculation of soil nailing wall displacement is less.In most cases,the soil is regarded as an elastomer for displacement calculation.Based on previous research results and considering the stress characteristics of soil nailing support structure when the slope angle was small,this paper calculated the earth pressure when the slope angle was small,then calculated the internal force of soil nailing by combining with the empirical distribution form of earth pressure,and then the displacement of soil nailing wall by considering the elasto-plastic deformation characteristics of soil was calculated.The specific research contents and conclusions are as follows:(1)By analyzing and summarizing the mechanism of soil nailing support structure,the mechanical characteristics of soil nailing support structure under normal working condition were understood,and the earth pressure of soil nailing wall with small slope angle was calculated based on the limit equilibrium analysis method;the empirical distribution forms of earth pressure on Tschebtairoff medium clay was combined with the above calculation method of earth pressure of soil nailing wall,and the calculation formula of soil nailing tension along the depth of foundation pit was derived;then,it was assumed that the shear force between nails and soil was a double triangle model along the axial direction of soil nails,and according to the relationship between the shear force and the tensi on of soil nails,the calculation formula of the axial distribution of soil nails tension was derived;(2)By analyzing and summarizing the action mechanism of the soil nail support structure,understand the force characteristics of the soil nail support structure under normal working condition;it was concluded that the horizontal displacement of soil nailing wall can be simplified as the superposition of three parts: the displacement caused by excavation of foundation pit,the displacement reduced by soil nailing in passive area and the displacement increased by soil nail ing in active area;considering the elastic-plastic deformation characteristics of soil,the calculation formulas of three parts of displacement and soil nail tension deformation were derived;then,according to the deformation coordination condition of sl ope surface,the calculation formula of soil nailing wall slope surface displacement was proposed;finally,combined with engineering examples,the geotechnical finite element software Plaxis3 D was used to simulate the construction process of soil nailing foundation pit to analyze the consistency between the theoretical calculation results in this paper and the Plaxis3 D calculation results,thereby verifying the rationality and feasibility of the theoretical calculation method;(3)Based on a soil nailing foundation pit,eight important factors affecting the horizontal deformation and stability of soil nailing foundation pit(overload value outside the pit,soil weight,soil cohesion,internal friction angle of soil,slope angle of soil nailing wall,diameter of soil nailing,length of soil nailing,horizontal spacing of soil nailing)were selected for analysis,and the sensitivity of the eight factors was evaluated by grey correlation analysis method;through the analysis of uncontrollable parameters,it was found that the soil weight and overload outside the pit were the most sensitive to the maximum horizontal displacement of the foundation pit,while the soil cohesion and internal friction angle were the most sensitive to the stability of the foundation pit;through the analysis of the design parameters of the support structure,it was found that the slope angle and the horizontal spacing of soil nailing were the most sensitive to the maximum horizontal displacement of the foundation pit,while the diameter and length of soil nailing were the most sensitive to the safety factor of the stability of the foundation pit.