Study On The Influence Of Joints On The Stability Of Surrounding Rock In Loess Tunnel

In recent years,a large number of loess tunnels have appeared in the construction of high-grade highways in China.However,during the construction and operation of a large number of loess tunnels,safety accidents such as tunnel lining cracking and partial landslide occurred.Analysis of the causes and damages of the surrounding rock instability of typical loess tunnels shows that the internal joint development of loess soil is one of the main reasons for the instability of surrounding rock of all loess tunnels.Therefore,it is urgent to carry out research on the influence of joints on the stability of loess tunnels.Based on this background,this paper collects and analyzes a large number of measured data of surrounding rock of loess tunnel in Zhengxi high-speed railway tunnel project.Combined with the characteristics of current domestic loess tunnel construction,the finite element software MIDAS GTS NX is used to establish the stability of surrounding rock of loess tunnel considering joint.Based on the analysis model,the paper analyzes the specific effects of joint group number,joint position and joint inclination on the stability of loess surrounding rock.The main conclusions obtained are as follows:(1)The more joints in the surrounding rock of the loess tunnel,the worse the integrity of the surrounding rock of the tunnel,the less obvious the soil arching effect,the greater the deformation of the surrounding rock of the loess tunnel,the lower the Mises stress of the surrounding rock,and the waist of the tunnel At the surrounding rock,the Mises stress gradually increases.(2)The surrounding rock joints of the loess tunnel are distributed at different locations,and the displacement fields of the surrounding rock of the tunnel are as follows: the maximum displacement of the dome is the second,and the displacement of the arch waist is second.The closer the joint is to the edge of the tunnel,the greater the difference in the displacement of the surrounding rock on both sides of the joint.The closer the joint is to the middle of the tunnel vault,the smaller the displacement difference of the surrounding rock on both sides of the joint;the joints are on the side of the tunnel,the arch waist,the arch shoulder and the arch.At the top,the maximum Mises stress of the surrounding rock at the arch waist is gradually increasing,while the minimum value appears at the vault and the bottom,which tends to decrease gradually.(3)With the increase of the joint inclination angle,the displacement of the surrounding rock at the tunnel vault gradually becomes smaller and the stability gradually increases.With the increase of the joint dip angle,the difference of the displacement of the soil on both sides of the joint gradually increases,and the joint two The deformation of the soil in the side soil near the tunnel surface is gradually weakened by the strong,and the difference gradually decreases with the increase of the inclination angle.(4)The different joint factors of the surrounding rock joints of the loess tunnel have different effects on the stability of the surrounding rock.Among them,the influence of the joint inclination is the most obvious,followed by the number of joints,and finally the joint position.(5)When designing the loess tunnel,it should be considered to pass through as many joints as possible,and at the same time control the joint position as much as possible at the top of the tunnel arch and the joint direction of the tunnel section to reduce the joint to the loess tunnel.The influence of surrounding rock stability.