浅埋小净距隧道合理净距及围岩稳定性分析

Analysis on Reasonable Clear Distance and Stability of Surrounding Rock of Shallow-buried Small-distance Tunnel

以贵州盘兴高速公路司家寨小净距隧道工程为例,采用有限差分法对不同净距下的小净距隧道进行了数值模拟研究,对比分析其拱顶沉降、拱底竖向位移、中夹岩竖向位移及剪应变增量的变化规律,探讨Ⅴ级围岩下的隧道合理净距以及围岩稳定性。结果表明:净距较小时隧道左右洞开挖的应力叠加效应明显,随着净距的减小,计算的各数值明显增大,围岩特别是中夹岩极有可能发生屈服破坏甚至失稳;小净距隧道选择净矩D为10 m较为合适。隧道的最大变形出现在拱顶、拱底靠近中夹岩柱方向约20°左右位置,而中夹岩的最大变形主要出现在中岩体靠近开挖断面位置且处于上下分布。

The numerical simulation study for small-distance tunnel under different clear distances is carried out by adopting finite difference method based on Sijiazhai small-distance tunnel project of Guizhou Panxing Expressway, comparatively analyzing the variation rules of crown settlement, arc bottom vertical displacement, middle rock vertical displacement and shearing strain increment and discussing the tunnel reasonable clear distance and stability of surrounding rock for V class surrounding rock. The results show that when the clear distance is small, Stress suppeposition effect of the excavation of the left and right tunnel holes is significant. With the decreasing of clear distance, the calculated numerical values are increasing significantly, leading to the yield failure even unstability of the surrounding rock especially middle rock possibly. The excavation clear distance selected D = 10 m for small-distance tunnel is more appropriate. The maximum deformation of the tunnel appears on the vault and the place where the arc bottom approaches the middle rock column for about 20~, while the maximum deformation of the middle rock mainly appears on the position where the middle rock approaches the excavation section and is distributed up and down.