软塑黄土二元地层隧道变形特征及监测分析

当隧道斜向上穿越软塑黄土夹层时,隧道拱部逐渐脱离软塑黄土层,使得围岩处于"上硬下软"的二元地层状态。由于软塑黄土含水率高、稳定性差、承载力低,使得大断面隧道在这种二元地层下的变形特征不尽相同。本文依托银西高铁上阁村隧道,基于室内试验、数值计算、现场监测等手段,分析"上硬下软"二元地层下隧道围岩位移演化规律,揭示隧道围岩变形特征。结果表明:随着软塑黄土层的下移,拱顶累积沉降量逐渐减小并趋于稳定;当软塑黄土分布于边墙时,围岩软弱,软塑黄土变形量大,变形时间长;当软塑黄土分布于隧底时,隧底围岩隆起值及下台阶水平收敛较大;随着隧道穿出软塑黄土层,净空收敛逐渐减小并趋于稳定。

Deformation Characteristics and Monitoring Analysis of Tunnel in Soft-plastic Loess Binary Stratum

When the tunnel crosses the soft-plastic loess interlayer obliquely,the arch of the tunnel gradually breaks away from the soft-plastic loess layer,which makes the surrounding rock in the"upper hard and lower soft"binary stratum state.Due to the high water content,poor stability and low bearing capacity of soft plastic loess,the deformation characteristics of large cross-section tunnel in this binary stratum are different.At the background of Shanggecun Tunnel of Yinchuan-Xi’an High-speed Railway,this paper analyzed the displacement evolution law of tunnel surrounding rock under the binary stratum of"upper hard and lower soft"and revealed the deformation characteristics of the rock based on laboratory test,numerical calculation,on-site monitoring and other means.The results show that the cumulative settlement of the vault decreases and tends to be stable with the downward movement of the soft plastic loess layer.When soft-plastic loess distributes in the side wall,the surrounding rock is weak,the deformation of soft plastic loess is large and the deformation time is long.When soft-plastic loess distributes at the bottom of tunnel,the uplift value of surrounding rock and the horizontal convergence of lower steps are larger.As the tunnel passes through the soft plastic loess layer,the convergence of clearance gradually decreases and tends to be stable.