川西北某拟建高速公路隧道口高位危岩特征及危险性评价

Characteristics and Risk Assessment of High Altitude Dangerous Rock at the Portal Area of a Proposed Expressway Tunnel in Northwest Sichuan

某拟建高速公路隧道口位于川西北岷江河谷地带,区内地形地貌复杂、新构造运动强烈,高位危岩极其发育,严重威胁拟建公路隧道口。本文基于无人机倾斜摄影及现场调查,采用Rockfall Analyst软件模拟落石三维运动特征。结果表明:(1)危岩区坡度较陡,岩性以砂质千枚岩为主,岩体破碎、节理裂隙发育,稳定性较差,变形破坏模式以滑移式、坠落式为主;(2)落石运动过程以自由飞落、碰撞弹跳以及贴坡运动为主,最大速率33 m/s,最大弹跳高度14.5 m,最大能量约3 100 kJ,在运动过程有大部分会落至隧道洞口上方,危险性高-极高;(3)建议清除隧道洞口上方孤石、危岩,设置锚索(杆)框格梁进行处治,隧道进口接长明洞,同时加强监测。本研究成果对川西北地区公路、铁路工程地质选线、勘察设计及防灾减灾具有一定指导和借鉴意义。

A proposed expressway tunnel is located in the Minjiang River valley in northwest Sichuan Province,where the terrain is complex,the neotectonic movement is strong,and the high-altitude dangerous rock has highly developed,which seriously threatens the proposed expressway tunnel.This paper,based on UAV tilt photography and field investigation,and Rockfall Analyst software,simulates the three-dimensional motion characteristics of falling rocks.The results show that:①the slope of the dangerous rock area is steep,the lithology is mainly sandy phyllite,the rock mass is broken and the joints are developed,the stability is poor,and the deformation and failure modes are mainly sliding and falling;②The rockfall movement is dominated by free flying,collision bounce and slope sticking movement,with the maximum speed of 33m/s,the maximum bounce height of 14.5 m and the maximum energy of about 3100 kJ.Most of the rockfall will fall to the top of the tunnel entrance during the movement,and the risk is high to extremely high;③It is recommended to remove isolated rocks and dangerous rocks above the tunnel portal,set up anchor cable for treatment,and lengthen open holes at the tunnel entrance,while strengthening monitoring.The results of this study can be used to guide the highway and railway engineering geological line selection,investigation and design and disaster prevention and reduction in northwest Sichuan.