Abstract：Abstract ： Research purposes ： The slope is high and steep, and there exists unstable rockfall above the Pingshang tunnel entrance. Instability of unstable rockfall that has sudden and concealment, caused great harm, and seriously afected the railway construction and operational safety. This paper analyzed and researched the formation mechanism , unstable models of unstable rockfall at Pingshang tunnel entrance and movement characteristics after the destruction , to determine instability rolled probability and path of the unstable rockfall , put forward targeted remediation and protection measures , and also provided research , analysis , calculation methods and engineering protection measures when exist unfavorable geological hazards that unstable rockfall in other mountain railway. Research conclusions ： (1) Based on the investigation and the actual measurement of the unstable rockfall , the unstable models of unstable rockfall above the Pingshang tunnel entrance are divided into four types. (2) Through simulating the movement characteristics of the rockfall , identify that about six percent of the unstable rockfall instability above the Pingshang tunnel entrance will cause danger to the tunnel entrance and bridges. (3) Put forward prevention measures and the specific location of protection , to ensure the railway construction and operational safety. (4) The research results can be applied to survey and design of unstable rockfall unfavorable geological engineering.
2015, Vol. 32 
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