深埋老黄土隧道变形规律及初支受力机理

为了解决深埋老黄土隧道初期支护因围岩弱化挤压而破坏的现象,为隧道支护破坏整治提供依据,以阳山隧道出口深埋老黄土段为工程依托,对不同含水率下隧道变形规律进行了统计分析,然后综合采用变形反演、强度折减数值计算和实测支护内力规律对比的方法对初期支护的整体受力状态和受力规律进行了研究,最后通过数值计算对初期支护受力关键部位的破坏过程和破坏机理进行了分析。得到如下结论:(1)深埋老黄土隧道变形规律与围岩含水率相关,在围岩含水率低于老黄土塑限前,隧道的变形量小、稳定速度快、拱顶沉降大于水平收敛,含水率大于塑限后,隧道变形量显著增加、持续时间长、水平收敛大于拱顶沉降;(2)初期支护全环整体处于小偏心受压模式,受力关键部位为拱部,随着围岩的不断弱化,支护小偏心受压模式不变、内力逐渐增加,最大内力由拱腰转移至拱脚处;(3)在小偏心压力作用下支护结构为“压-剪”控制破坏,表现为混凝土表面压碎剥落、内部斜向剪切破坏,锁脚锚管的存在对结构破坏发展方向有引导作用,使得结构由“X”型对称剪切破坏转化为固定方向的斜截面剪切破坏。建议支护破坏整治方案采用可提高结构斜截面抗剪强度的加强措施,或采用限阻耗能型支护来释放围岩压力并减小结构内力。

Deformation Law and Mechanical Mechanism of Deep Buired Old Loess Tunnel

In order to provide countermeasures for the problem of primary support failure caused by the weakening and squeezing of surrounding rock in deep buried old loess section at the exit of Yangshan tunnel, a statistical analysis of the deformation law under different moisture content was made. Then the overall stress state and mechanical laws of the primary support was researched combining the methods of deformation inversion, strength reduction and mechanical laws, and comparison of the measured internal force law. Finally, the failure process and mechanism in numerical calculation of the key part of the primary support were analyzed through numerical simulation. The conclusions are as follows: (1) The deformation law is related to the moisture content of the surrounding rock. When the moisture content is lower than the plastic limit of old loess, the deformation amount of the tunnel is small, the stabilization speed is fast, and the vault settlement is greater than horizontal convergence. After the moisture content goes greater than plastic limit, the deformation amount significantly increases, the duration is long, and the vault settlement is less than horizontal convergence. (2) The whole primary support is in the state of small eccentric compression, and the key part under stress in the support ring is the arch. With the continuous weakening of the surrounding rock, the internal force gradually increases while the small eccentric compression mode is unchanged, and the position of maximum internal force is transferred from the arch waist to foot. (3) The failure is controlled by compression-shear strength under small eccentric compression, which manifests as surficial crushing and peeling off and internal oblique shear failure. The existence of locking foot bolts has a guiding role in the development of failure, which transforms the "X" shape symmetrical shear failure to oblique shear failure with fixed direction. It is suggested that the countermeasures of support failure should be either reinforcement measures (significantly improve the compress and shear strength) or yielding measures (release the rock pressure and reduce the support internal force).