北京地铁浅埋暗挖区间隧道塌陷机理

结合北京典型地质条件和区间隧道的断面形式，将城市浅埋暗挖隧道分为超浅埋隧道和浅埋隧道两种，对于超浅埋隧道，隧道的破坏形式主要是整体下沉和塌陷，隧道的破裂角接近80°；对于浅埋隧道，破坏形式以滑裂破坏为主，规范给出的滑裂角为45°φ／2，但通过对北京地铁事故的调查研究发现，隧道滑裂角大于45°＋φ／2，因此应用土力学原理和Mohr—Coulomb破坏准则推导出新的地层滑裂角．结果表明，浅埋隧道的破裂角与隧道的覆跨比、矢跨比有关，且比45°＋φ／2大10°～15°．运用FLAC3D软件计算分析隧道破坏时塑性区分布情况和破坏过程，并与实际工程监测数据对比，发现新的滑裂角更接近实际工程的破坏情况．

Study on mechanism of collapse based on shallow buried subway tunnel of Beijing

Combining the typical geological conditions and tunnel cross-section of Beijing subway, this paper divides city-shallow tunnel into two cases： the special shallow tunnel and the general shallow tunnel. For the special shallow tunnel, the destroy form is mainly the whole subsidence and collapse, the angle of rupture is nearly 80°. For the general shallow tunnel, the standards give the slipping angle 45° ＋ φ/2, but the in-situ monitoring of Beijing subway shows that the stratum slipping angle is higher than 45° ＋ φ/2. Therefore, this article deduces a new stratum slipping angle by using soil mechan- ics principle and Mohr-Coulomb failure criteria, which found that the new slip angle changes according to different cover thickness-span ratio and height-span ratio with the frictional angle between 45° to 80°. Then, the failure process is analyzed by FLAC3D. The results show the new slip angle is closer to the actual damage condition compared with the actual monitoring data.