黄土隧道围岩工程特性及纵向位移分析

Analysis on the Engineering Characteristics and Longitudinal Displacement of the Surrounding Rock in Loess Tunnel

以采用台阶法施工的兰渝铁路黄土隧道为背景,通过三轴固结排水剪切试验分析黄土隧道围岩的工程特性,采用FLAC3D对隧道施工过程进行模拟,选取双线性应变硬化/软化遍布节理模型模拟黄土隧道围岩的工程特性,研究黄土隧道围岩的纵向位移。结果表明:隧道开挖扰动破坏了黄土隧道围岩的结构性;黄土隧道围岩的摩尔破坏包络线为双线性折线;黄土隧道围岩垂直节理遍布发育;围岩纵向位移总体上是边墙处小于拱顶处,围岩先期纵向位移约占总纵向位移的33%～41%,随着掌子面推进围岩纵向位移趋于稳定;预留核心土可有效地控制围岩纵向位移和塑性区的发展,有利于掌子面的稳定和施工安全;掌子面空间约束效应的影响范围约为-4R～4R(R为隧道开挖当量半径);由本文模型预测的围岩先期纵向位移与既有理论结果相符,但更能反映黄土隧道围岩的工程特性。

Taking the loess tunnel constructed by bench method of Lanzhou-Chongqing Railway as background, the engineering characteristics of the surrounding rock in loess tunnel were analyzed by triaxial consolidated-drained shear test and the construction process of tunnel was simulated by FLAC3D. Bilinear strain-hardening/softening ubiquitous-joint model was selected to simulate the engineering characteristics of the surrounding rock in loess tunnel as well as to study its longitudinal displacement. Results show that the structure of the surrounding rock in loess tunnel is broken by tunnel excavation disturbance. The Mohr failure envelop of the surrounding rock in loess tunnel is double linear broken line. The vertical joint of surrounding rock is all over developed in loess tunnel. The longitudinal displacement of the surrounding rock at side wall is smaller than that at the crown as a whole. The preexisting longitudinal displacement of surrounding rock takes up about 33%~41% of the total longitudinal displacement. Along with the advance of tunnel face, the longitudinal displacement of surrounding rock tends to be stable. The reserved core soil can effectively control the development of the longitudinal displacement and the plastic zone, which is beneficial to tunnel face stability and construction safety. The influence scope of tunnel face space constraint is -4R^4R (R is the equivalent radius of tunnel excavation). Using the bilinear strain-hardening/softening ubiquitous-joint model, the prediction of the preexisting longitudinal displacement of surrounding rock agrees with the existing theoretical result. However, it can better reflect the engineering characteristics of the surrounding rock in loess tunnel.