小间距浅埋隧道的支护设计探讨

DISCUSSION ON SUPPORT SYSTEM BETWEEN TWO PARALLEL CLOSELY-SPACED SHALLOW TUNNELS

利用奥地利大型岩土工程有限元数值计算软件FINAL计算结果比较研究认为,在新奥法施工的小间距平行土质浅埋隧道中,对于中间岩柱的支护与设计,只要衬砌受力在合理范围内,不需要特别考虑中间岩柱的稳定性,而对其加设锚杆或者其他支护辅助手段,隧道之间的间距可以达到1.0 m,甚至更少。列举了慕尼黑地铁隧道对这一结果的成功应用。对于近距离双孔平行隧道,两隧道相互之间的影响,不仅与围岩类别、隧道间距、开挖和支护方式有关,而且不同的开挖顺序,会有不同的结果。分析结果表明,如果先修建好一孔隧道,再修建另一孔隧道,第二孔隧道的修建会对第一孔隧道,特别是相近一侧有较大的影响,仰拱处容易出现拉应力;如果两孔隧道同时交替掘进,则隧道相互影响较大,第一孔隧道的底部和第二孔隧道的拱部,容易出现拉应力,总体衬砌受力比第一种开挖支护方式要小。两种开挖支护方式中,中间岩柱两侧土体和衬砌均处于受压状态。慕尼黑地铁U6段相距0.8 m,两隧道的成功修建和运营,是对本文结论的成功验证。

The support system between are analyzed and discussed. It is found that, if the forces in the lining are less than the limit ones during and after excavation, there is no need to consider bolt or other assistant support methods for the surrounding rock between two tunnels. The distance between two tunnels can be 1.0 m, or even more narrow, as Munich subway had done. For closely-spaced tunnels, the excavation sequence has visible impact on the both tunnels. If one tunnel is finished firstly and the other is completed subsequently, results show that the first tunnel has larger compression forces in the lining and even some tension happens at the invert of the lining during the excavation of the second tunnel. If the two tunnels are excavated by alternant way, the surrounding rock between the two tunnels has more disturbances. The crown of the second tunnel and the invert of the first tunnel are easy to be in tension. But generally, the forces are less than the ones when the tunnels are excavated in the first sequence. For both excavation sequences, the surrounding rocks between the two tunnels are both in compression. Munich subway which had been built successfully validated the dependability of the results.