Characteristics and Risk Assessment of High Altitude Dangerous Rock at the Portal Area of a Proposed Expressway Tunnel in Northwest Sichuan
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:① the 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;② The 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 3 100 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;③ It 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.
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