某铁路隧道底部结构隆起病害成因分析及治理对策探讨

西南地区YD隧道长约7 850 m,设计时速200 km,系双块式无砟轨道;建成通车后,K108+600~K109+350等区段底部结构出现不同程度的隆起,引起无砟轨道板开裂、破坏,致使轨道几何尺寸处于不稳定状态,影响列车正常运营。该隧道病害段穿越地层为薄至中厚中风化泥岩、砂岩缓倾互层围岩体,地应力测试表明该段存在与隧道轴线近似垂直的水平高地应力。通过采用现场调查测试、理论分析和数值计算等手段,分析总结认为该隧道底部结构隆起的主要成因是:1)以水平构造应力为主导的极高地应力作用于隧底下伏薄至中厚缓倾互层围岩体;2)仰拱参数不满足工程所处的地质环境。在锚索加固治理方案实施后,YD隧道的底部结构隆起依然没有稳定,在分析其原因、经验、教训的基础上提出治理及今后遇到类似工程的方向性建议:1)在缓倾互层围岩体环境中且埋深50~300 m的隧道工程中,应特别重视底部结构的针对性设计,恰当选择仰拱的矢跨比和刚度;2)锚索必然的松动、滑移特征决定了其不能作为隧底结构隆起病害整治的单独和主要技术手段,以低预应力锚杆锚固、至少是"刚柔相济"的方式应被重视。

Analysis on Causes for and Renovation of Floor Structure of a High-speed Railway Tunnel Located in slightly-dipping Interbedded Rock Mass

Y. D. Tunnel, designed with a speed of 200 km and double block ballastless track, in Southwest China is about 7.85 km in length. Varying degrees of heaving appeared in the floor structure of the tunnel within the region of K107+970～K109+270 after it was put into service. Cracks and failure developed in the ballastless tracks, resulting in track geometry changing in an unstable state. The railway operation was seriously influenced. The tunnel was located in low medium thick interbedded strata of medium weathered mudstone and sandstone. The in situ stress was measured, indicating that there existed high horizontal stress nearly perpendicular to the tunnel axis. In the paper, the causes for the heaving of the floor structure of the tunnel are analyzed by means of field survey and measurement, theoretical analysis and numerical simulation. It is concluded that the causes for the heaving of the floor structure are as follows: 1) Super high ground stress, mainly taking the form of horizontal structural stress, acts on the slightly dipping interbedded low medium thick rock mass underlying the tunnel floor; 2) The parameters of the invert cannot meet the requirements of the geological conditions. The following countermeasures are proposed for the treatment of the floor heaving: 1) For tunnels located in slightly dipping interbedded rock mass and under 50 m～300 m cover, special attention should be paid to the specific design of the floor and appropriate rise span ratio and rigidity should be selected for the tunnel invert; 2) Due to the loosening and sliding features of the anchor cables, the anchor cables cannot be taken as the only or major technological measures to control the heaving of the tunnel floor; on the other hand, rock bolting, at least “rigid control measures + flexible control measures” should be taken to control the heaving of the tunnel floor.