软岩隧道的超前导洞施工位置优化数值分析

Numerical Analysis on the Optimization of the Position of the Pilot Tunnel in Soft Rock

采用数值软件FLAC 3D建立了不同超前导洞位置工况的计算模型,计算了在不同布置形式下围岩位移、应力特征和支护结构受力响应。导洞的位置分别设置在正洞左右两侧、上下两侧以及正洞中央。对比分析了超前导洞位置对控制软岩隧道变形的有效性。结果表明超前导洞应力释放效果与导洞布设位置有关,当导洞位于正洞外侧时,若导洞与正洞距离较近会影响正洞的稳定性,需要对导洞与正洞之间的围岩进行加固。若导洞与正洞距离较远,应力释放效果不佳。因此,建议超前导洞设置在正洞中央。导洞设置在正洞断面中央对变形控制效果最佳,更利于围岩的应力释放。"边让边抗"的支护方法可以控制围岩塑性区的发展。

Numerical models of different positions of pilot tunnel are established using FLAC 3 D to calculate the displacement,stress characteristics of surrounding rock and stress of supporting structure. The locations of the pilot tunnel are set at the left and right sides,the upper and lower sides and the centre of the main hole,respectively. The effectiveness of the location of the pilot tunnel for controlling the deformation of the soft rock tunnel are compared and analyzed. The results show that the stress release effect of the pilot tunnel is related to its location. When the pilot tunnel is excavated outside the main tunnel,the pilot tunnel will affect the stability of the main tunnel if it is close to the main tunnel. It is necessary to reinforce the surrounding rock between the pilot tunnel and the main tunnel.However,it is less effective if the pilot hole is far from the main hole. Therefore,the pilot tunnel is suggested to be set at the centre of the main tunnel since it is more effective to control the ground displacement and more conducive to the stress release of the surrounding rock. The support method of"yielding and resisting"can control the development of plastic zone of surrounding rock.