正断层倾角变化对其下盘隧道围岩影响的研究

Study on the Influence of Dip Angles of Normal Fault on Tunnel Surrounding Rocks in the Fault Footwall

对在正断层下盘开挖隧道时,断层倾角β对隧道围岩的影响进行了研究.研究发现,β=53°是隧道围岩位移、应力和安全系数等变化的一个转折点;当β为90°～53°时,断层发生了下盘向下移动的活化,断层由正断层转化为逆断层,当β<53°时,断层两盘都有向下的位移,且上盘的位移要大些;断层破碎带对隧道开挖导致的变形有明显的屏蔽作用,这种屏蔽作用主要发生在断层倾角较陡时的情形;隧道围岩最大位移主要分布在隧道的顶部,且围岩最大位移-断层倾角β关系曲线呈近似的"U"字形;围岩强度按安全系数进行折减后就可得到隧道的失稳或破坏状态,隧道围岩稳定安全系数-断层倾角β关系曲线呈近似屋脊形,当β=53°时安全系数最大.结果表明,β的变化对隧道围岩的位移、应力和稳定性有重要影响.

By using numerical simulation method, we studied the influence of dip angle （fl） of normal fault on the tunnel surrounding rock when excavating in the fault footwall. The results shows thatβ=53° is a turning point of variations of the stress, displacement and safety factor, et al, of surrounding rock. Whenβis ranging from 53° to 90°,the fault becomes reactive and the footwall moves downward, thus the activated fault will change from normal fault to re- versed one. Whenβ=53°, both the two fault walls move downward and the displacement of upper wall is larger than that of the footwall. Meanwhile, the fault fracture zone has obvious shielding effect on the deformation caused by tunnel excavation, and the shielding effect is more obvious when/3 gets steeper. The maximal displacement of tunnel surrounding rock main- ly locates in the top of tunnel, and the relation between the maximal displacement and dip angle βis an approximate ＂U＂ shape. Additionally, the unstable state of surrounding rock can be obtained when the rock strength is deducted by the safety factor. The relation between the safety factor and βis an approximate ridge shape, and the safety factor is maximal whenβ=53°. Therefore, the variation of fault dip angle has significant influence on the stress, displacement and stability of tunnel surrounding rock.