Study On Design Load Of Earth Pressure In High-filled Cut-and-Cover Tunnel

With the continuous development of China’s western region,in the continuous improvement of traffic network,it is bound to appear high-filled cut-and-cover tunnel.In view of the inexperience of earth pressure load criteria and calculation values for high-filled cut-and-cover tunnels structures.This paper from the cut-and-cover tunnels structure and the actual stress state of filling soil,it comprehensively considers the influencing factors such as the width of cut-and-cover tunnels,section type,filling property,slope angle and the ratio of groove width,and uses numerical simulation to analyze and study the changing law of each influencing factor,and puts forward the proposed formula for calculating the vertical earth pressure at the top of high-filled cut-and-cover tunnels and the suggested formula for calculating the lateral earth pressure around the cut-and-cover tunnels.The main research contents are as follows:(1)This paper is based on numerical simulation,it uses mathematical regression method to get the proposed formula for calculating the vertical earth pressure at the top of cut-and-cover tunnels and the suggested formula for calculating the lateral earth pressure around the cut-and-cover tunnels.Two design schemes of railway cut-and-cover tunnels are selected for verification,the results are in good agreement,which verifies the correctness of the proposed formula in this paper.(2)During the study of the proposed formula for calculating the vertical earth pressure at the top of high-filled cut-and-cover tunnels,put forward the four vertical earth pressure influence coefficient,respectively is:cut-and-cover tunnels section shape influence coefficient kov,backfill soil elastic modulus influence coefficient kiv,cut-and-cover tunnels width influence coefficient k2v,slope angle theta and groove width ratio B/D coupling influence coefficient k3v.The analysis results show that the influence degree and trend of vertical earth pressure at the top of the cut-and-cover tunnels are different.The influence coefficients k3v and k1v can reduce the vertical earth pressure at the top of the cut-and-cover tunnels.The influence coefficient k2v will increase the vertical earth pressure at the top of the cut-and-cover tunnels.The influence coefficient kov on the vertical earth pressure at the top of the cut-and-cover tunnels can be basically ignored.(3)According to the lateral earth pressure calculation method provided by the code,this paper further studies the lateral earth pressure coefficient around the cut-and-cover tunnels.Four influence factors are proposed for the lateral earth pressure coefficient λ given by the code,respectively is:cut-and-cover tunnels section shape influence coefficient k0H,properties of backfill soil influence coefficient kiH(including filling modulus of elasticity influence coefficient kiHE,filling internal friction angle influence coefficient k1Hφ and filling cohesion influence coefficient k1Hc),cut-and-cover tunnels width influence coefficient k2H,slope Angle theta and groove width ratio B/D coupling influence coefficient k3H.The results show that the trend of their influence on the lateral earth pressure around the cut-and-cover tunnels is also different.The influence coefficients kiHφ and k2H can reduce the lateral earth pressure coefficients around the cut-and-cover tunnels,while the influence coefficients k1HE can increase the lateral earth pressure coefficients around the cut-and-cover tunnels.The influence coefficients k0H on the lateral earth pressure coefficient depends on the shape of the section of the cut-and-cover tunnels.If it is an arch cut-and-cover tunnels,k0H=1,if it is a rectangular cut-and-cover tunnels,the lateral earth pressure coefficient will increase relative to the arch cut-and-cover tunnels.The influence coefficient kiHC=1,so the influence of internal friction angle on lateral earth pressure coefficient can be neglected.In addition,the influence coefficient k3H on the lateral earth pressure coefficient around the cut-and-cover tunnels increases or decreases,or even has no effect,which mainly depends on the coupling effect of slope angle and the ratio of groove width.