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以张涿高速公路张家口段朱家峪Ⅱ号隧道为工程背景,采用FLAC3D软件,讨论不同仰拱封闭距离对台阶法开挖隧道稳定性的影响,并与现场监测数据进行对比分析。研究结果表明:仰拱与上台阶设置的初次支护形成封闭的承载环,使围岩的受力状态由不利于稳定的双向受力状态转变为有利的三向受力状态,从而使围岩保持稳定,仰拱跟进速度越快,围岩稳定性越好,考虑到让压因素,仰拱封闭距离宜确定为2～3倍洞径。仰拱封闭距离对于类似隧道的仰拱支护优化及现场施工具有参考意义。
Taking Zhangjiakou Section No.2 of Zhangjiakou Expressway of Zhangjiakou Expressway as an example, the FLAC3D software was used to discuss the influence of different closing distances of upturns on the tunnel stability of step excavation, and compared with the on-site monitoring data. The results show that the inverted arch and the first support provided by the upper step form a closed bearing ring, which makes the stress state of the surrounding rock change from a bi-directional stress state unfavorable to stability to a favorable three-direction stress state so that the surrounding rock Maintaining stability, the faster follow-up arch inversion, the better stability of the surrounding rock, taking into account the pressure factor, the closing distance of the inverted arch should be determined as 2 to 3 times the diameter. The closing distance of invert arch has reference significance for the optimization of the arch support and the on-site construction of similar tunnels.