动荷载作用下隧道围岩块体稳定性分析及其应用

隧道围岩中的结构面将岩体切割成块体，块体在自然状态下的静力平衡因为隧道开挖而被打破，临空面的产生和动荷载的施加都可能导致块体的滑移，进而引起围岩失稳。以往应用块体理论寻找关键块体时，多只考虑纯重力的作用，而忽视了爆破振动、地震等动荷载对诱发失稳灾害的重要作用。将爆破振动荷载和地震荷载转化为等效静力，并通过数学计算求出使块体安全系数最低的动荷载方向，再利用关键块体理论矢量分析方法分析隧道围岩的稳定性。在长岗隧道中的应用表明，考虑动荷载作用下的块体安全系数明显小于只考虑重力作用时的安全系数，原本稳定的块体也可能在动荷载作用下变成关键块体导致围岩失稳，这与长岗隧道现场记录的破坏现象相符。

Stability analysis of surrounding rock mass of tunnel under dynamic load and its engineering application

Surrounding rock of tunnel is cut into blocks by structural planes. Tunnel excavation breaks the mechanical balance of the blocks in the natural state. Dynamic loads may promote the slip of a block toward a free surface, which will cause the failure of surrounding rock. However, most applications of block theory only consider the effect of gravity without taking blasting vibration load and seismic load into account. Blasting vibration load and seismic load are transformed into equivalent static loads, and the most unfavorable direction of dynamic load is calculated where the safety factor of block is the lowest. The vector analysis method of block theory is applied to analyze the stability of surrounding rock mass in tunnel considering the effect of dynamic load as well as gravity. The calculated results for Changgang tunnel show that the safety factor of block under dynamic load is obviously lower than that only considering the effect of gravity. Under the action of dynamic load, the original stable block can be turned into a key block and leads to surrounding rock failure, which is consistent with the actual destruction phenomenon recorded in Changgang tunnel.