在高地应力作用下近水平岩层隧道掌子面稳定性分析及控制*

为了研究大峡谷隧道开挖中掌子面大范围塌方及支护失效问题，分析现场水平层状围岩失稳特征，基于3DEC离散元软件探究掌子面失稳机理，提出塌腔处治及支护整体优化控制措施。研究结果表明:掌子面塌方主要表现为顺层滑移、挤压离层、局部掉块。开挖后拱顶沿水平层理面发生离层，导致掌子面分层垮落，层间错动掉块。围岩拱顶块体呈斜向下45°变形发展，掌子面中部和底部呈平行隧道轴向变形发展，根据塑性区和剪切滑移区扩展范围，最终形成宽5 m、高4 m的塌腔，掌子面前方岩体受影响深度3~4 m。对易塌方段提出台阶法开挖等控制措施，现场监测洞周位移收敛量不超过5 cm，整体优化后支护效果明显。

Stability analysis and control of tunnel face in near horizontal strata under high ground stress

In order to study the problems of large-scale collapse and support failure of the tunnel face during the excavation of the Grand Canyon tunnel,the instability characteristics of the horizontal layered surrounding rock at the site were analyzed,then the instability mechanism of the tunnel face was explored based on 3DEC discrete element software,and the measures of the collapse cavity treatment and the overall optimization control of support were put forward.The research results showed that the tunnel face collapse mainly represented as the bedding slip,extrusion separation and local block falling.After excavation,the vault separated along the horizontal bedding plane,resulting in layered collapse of tunnel face and interlayer staggered block falling.The surrounding rock vault block presented the deformation development oblique downward with 45° angle,and the middle and bottom of tunnel face presented the deformation development parallel with the tunnel axis.According to the expansion ranges of the plastic zone and the shear slip zone,a collapse cavity with the width of 5 m and the height of 4 m was finally formed,and the rock mass in front of tunnel face was affected at the depth of 3~4 m.For the sections prone to collapse,the control measures such as bench excavation were proposed.The convergence of displacement around the tunnel monitored on site was not more than 5 cm,and the support effect was obvious after overall optimization.