| In recent years,with the implementation of the strategy of western development and the Belt and Road,the scale of engineering construction in the loess area of northwest China has gradually increased.In order to solve the problem of water shortage in Xi ’an area,the project of water diversion from Han to Wei came into being.This paper takes the shield tunnel in the Loess Plateau area of the Yinghanjiwei Phase Ⅱ Project as the engineering background,the shield tunnel faces complex geological conditions such as soft loess,shallow overcover soil,and large burial depth,and the existing literature does not have sufficient detailed research on the shield tunnel in the Loess Plateau area with complex address conditions.In this paper,by searching the literature and materials on the basic physical properties of Q2 loess and the earth pressure balance shield,this paper derives the calculation method of loose earth pressure at the top of the hole considering the incomplete soil arch effect based on the theory of loose earth pressure in Taishaki,and combines ABAQUS numerical simulation to analyze the sensitivity of the influencing factors.Aiming at the excavation of shield machine in uneven soft and hard formations,a theoretical model of shield shell-soil mechanics was established,and the sensitivity analysis of the influencing factors of shield attitude control was carried out by combining numerical simulation.The influencing factors such as the burial depth,the pressure of the soil silo of the shield machine,and the condensation hardening rate of the grouting material were established by finite element numerical simulation,and the excavation stability,surrounding rock deformation,and segment mechanical behavior of the tunnel under the large buried depth were studied.The results of the study showed that:(1)The degree of soil arching effect θ:The sensitivity of the influencing factors from large to small is the moisture content of loess layer,tunnel radius,formation loss,synchronous grouting pressure and grouting amount,load on the surface,segment stiffness.Except that the surface uniform load is negatively correlated with the degree of soil arching effect,the other influencing factors are positively correlated.(2)The calculation results of loose earth pressure in this paper are safer than numerical deflection,and the deflection moment generated by loose earth pressure will cause the attitude of the shield machine to be deflected,which provides a research basis for the establishment of the shield machine-soil mechanical interaction and the research on the pitch angle control of the shield machine.(3)Vertical displacement:the vertical force of shield-soil interaction is linearly positively correlated with displacement,and the vertical displacement of shield machine decreases with the increase of soil strength.In the soft and hard uneven stratum,the influence of shield machine settlement increases with the increase of the proportion of soft loess stratum.Pitch angle:With the gradual increase of the proportion of soft soil on the face of the palm and the bottom of the machine,the difficulty of controlling the pitch angle of the shield machine will also increase,and the pitch angle is positively correlated with the deflection moment in the vertical plane.Horizontal angle:With the continuous increase of the strength of the soil in the formation,the horizontal bending moment of shield shell-soil and the horizontal declination angle relationship of the shield machine changes from linear to parabolic.In the soft and hard uneven formation,the horizontal deflection angle of the shield machine gradually increased with the increase of the proportion of soft loess.(4)The dividing line of active and passive stress states of the soil on the face of the face has a linear correlation with the burial depth.Under the same buried depth,with the increase of the pressure of the soil silo of the shield machine,the soil mass of the face of the face changes from the active state to the passive state,the lateral surface settlement directly above the tunnel gradually decreases,and the surface settlement in the direction of the axis of the tunnel appears slightly uplifted after the face of the face.(5)The buried depth of the tunnel increases,and the rebound deformation of the top and bottom of the hole increases after shield excavation,reaching a maximum of 2～3 cm.Excessive rebound deformation may cause the earth pressure balance shield machine to jam or cause the segment to be damaged,and under the deep shield tunnel,with the acceleration of the condensation hardening rate of the elastic mold of the grouting material,the supporting effect of the grouting material on the tunnel is enhanced,and the force of the segment is reduced. |
