高地应力水平岩层隧道岩爆机制研究——以大峡谷隧道为例

Rockburst Mechanism of Daxiagu Tunnel in Horizontal Rock Formation with High Crustal Stress

高地应力水平层状硬脆性岩体隧道在开挖后周边应力会重分布,导致切应力增加,进而引起局部的弹性应变能增大,当达到一定程度后就会发生岩爆。为研究高地应力下水平岩层的岩爆机制,依托大峡谷超大埋深隧道,采用有限差分软件,建立水平岩层和均质岩层2种工况,从弹性应变能和应力路径2个方面分析了水平岩层岩爆的风险性。研究结果表明:1)在构造应力场的作用下,水平岩层与均质岩层存在较大差别。隧道开挖后,由于开挖卸荷作用,水平岩层掌子面所在环状区域应变能最大,且在开挖前后隧道周边不同位置都出现应变能突变;均质岩层开挖后应变能突变较小。2)应力路径中2种工况下最大主应力和弹性应变能的变化趋势一致,水平岩层中拱顶和拱底区域的应力差在开挖后不断增大,其他位置则在开挖到监测点所在断面时发生突变,造成岩石劣化,掌子面环状区域岩爆的风险增加。

The stress redistribution phenomenon would be induced after tunnel excavation in a horizontal layered hard and brittle rock mass with high ground stress,which would induce an increase in shear stress,thus resulting in an increase in local elastic strain energy and even rockburst phenomenon.To study the rockburst mechanism of horizontal rock formations under high ground stress,finite difference software is used and two working conditions of horizontal rock formation and complete rock formation are established based on the Daxiagu ultra-large deep tunnel.The rockburst risk of horizontal rock mass is analyzed from the aspects of elastic strain energy and stress path.The research results show that:(1)Under the action of the tectonic stress field,the difference between horizontal rock formation and complete rock formation is large.After tunnel excavation,the strain energy of the annular area where the face of the horizontal rock formation is located is the largest due to excavation unloading,and sudden changes of strain energy occur at different locations around the tunnel before and after excavation.The sudden change of strain energy is smaller after excavation of the complete surrounding rock.(2)The change trends of the maximum principal stress and elastic strain energy under the two working conditions in the stress path are the same.The stress difference between the arch crown and the arch bottom area in the horizontal rock layer increases after excavation,whereas in other areas,sudden changes occur when excavating to the section where the monitoring points are located,which would cause rock deterioration and an increase in the risk of rockburst in the annular area of the face.