| Based on the actual project of the Yinbai Expressway Yulinzi Water-rich Loess Tunnel,this paper systematically studies the deformation and damage law of the secondary lining of the tunnel and the long-term stability of the structure by means of field investigation,force monitoring,numerical simulation and analytical calculation,etc.The reinforcement scheme of the foundation of the steel pipe pile is proposed for the overall sinking of the secondary lining structure caused by the softening of the tunnel base,and the reinforcement effect and reinforcement process are analyzed and studied.The main results of this article are as follows:(1)The crack statistics and deformation monitoring of the secondary lining structure were carried out,and the fracture forms of the secondary lining structure were ring cracks and longitudinal cracks,the longitudinal cracks appeared in the tunnel vault and arch position,and the annular cracks appeared in the arch waist position;the secondary lining cross-sectional structure was in the overall settlement,and uneven settlement occurred along the tunnel longitudinal direction.(2)Real-time monitoring of the strain of secondary lining steel reinforcement was carried out,and the strain of the steel reinforcement was continuously increased with time,and the internal force of the structure showed a force state of "large right and left small" and "large and small under the bottom";the structural safety factor showed that the safety factor of each section gradually decreased over time,and whether it was in a safe state in the long-term operation process needed further study.(3)Numerical simulation study of the effect of surrounding rock softening on secondary lining structure was carried out,and the degree of surrounding rock softening was greater than that of surrounding rock softening on secondary lining structure.When the surrounding rock has a low moisture content,the secondary lining structure is deformed by the sinking of the vault and the uplift of the arch,the arch waist is extruded outward,and the internal force of the structure increases with the increase of the moisture content.When the surrounding rock has a high moisture content,the secondary lining structure sinks as a whole,and the internal force of the cross-section decreases significantly;as the softening range increases,the internal force of the structure increases continuously,but the increase is small.(4)Long-term stability analysis and numerical simulation analysis of secondary lining structure by surrounding rock creep were carried out.It can be seen from the analysis that with the increase of the water content of the surrounding rock,the load value of the structure gradually increases,the stress stability time of the structure gradually increases,and the value of the structural safety factor gradually decreases.The numerical simulation results show that the sedimentation of the secondary lining under the creep effect of the surrounding rock always occurs settlement deformation,the amount of settlement deformation in 100 years of creep is 51 mm,the internal force of the structure is gradually stabilized for 20 years,and the position of the structural arch and the side wall is prone to destruction.(5)Numerical simulation analysis of steel pipe pile reinforcement foundation that controls the settlement deformation of secondary lining is carried out,and the reinforcement effect is best when the reinforcement range of grouted steel pipe pile is 1 meter in diameter.The bearing process of steel pipe piles is divided into three stages.The first stage mainly bears the upper load with the foundation soil;the second stage is jointly stressed by the steel pipe pile and the foundation soil;and in the third stage,the steel pipe pile mainly replaces the foundation soil to bear the upper load. |
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