陡倾岩层双洞四线大跨暗挖地铁车站合理净距研究

Reasonable Clear Spacing for Large-Span Twin-Tube Four-Track Underground Metro Station in Steep Dip Rocks

当隧道轴线平行于陡倾岩层走向时,围岩开挖失稳风险随开挖跨度变大和隧道净距减小而显著升高,制定大跨度隧道在陡倾岩层中的合理净距对工程安全非常重要。以重庆轨道交通环线双洞四线大跨涂山站暗挖隧道为背景,对隧道轴线与陡倾岩层走向接近平行条件下采用双侧壁导坑法施工的2个超大跨近距离隧道,采用地质几何分析工程类比的方法,提出包含岩层破裂角θ的几何理论公式和最小隧道净间距计算方法,并结合数值模拟和施工试验段的监测反馈数据分析,确定地质偏压状态下近距离超大断面隧道的合理净距。结果表明:在隧道轴线与陡倾岩层走向接近平行状态下的近距离大跨隧道设计中结合岩层倾角考虑,将内侧隧道置于外侧隧道滑裂面之外,并由此推算出两隧道净距的方法是安全可靠的。

When the tunnel axis parallels to the trend of steep rock formation,the instability risk of the surrounding rock caused by excavation increases with the increasing excavation span and the decreasing tunnel clear spacing.Accordingly,the reasonable determination of clear spacing for large-span tunnel in steep rock formation is of great significance.A case study is conducted on twin-tube four-track mined Tushan station tunnel of Chongqing rail transit ring line.Then tunnel axis is parallel to trend of steep rock formation,and the two super-large small clear-spacing tunnels are constructed by double-side drift method.The geometric theory formula that includes a rock fracture angle ofθand the calculation method of minimum tunnel spacing are proposed using the methods of geogeometric analysis and engineering analogies.Then,the reasonable clear spacing of super-large cross-section tunnels under asymmetrical geological pressure is determined by analyzing the numerical simulation and the monitoring and feedback data of the construction test section.The results show that the clear spacing calculated by setting inside tunnel outside the sliding surface of lateral tunnel is safe and feasible when the tunnel axis is parallel to the trend of steep rock formation.