软弱土层隧道预支护及其参数优化研究

Tunnel Pre-support and Parameter Optimization under Soft Soil Layer

为了研究隧道穿越软弱土地层时的预支护措施,结合青海东部软弱土层隧道施工的案例,采用三维有限元计算模型模拟了隧道在管棚、小导管预支护及无预支护条件下的围岩稳定性变化规律,表明超前小导管注浆可以满足围岩稳定要求,并进一步对小导管在不同管径、环距、管长、开挖步长等支护参数条件下进行了探讨.研究表明:在不注浆情况下,单纯增大管长、管径、环距不能起到抑制围岩变形的作用;考虑管体注浆的情况下,随着剩余管长的增加,拱顶沉降值呈减小趋势,但存在某一临界长度,当剩余管长超过这一临界长度后,拱顶位移变化趋于稳定;对于软弱土层中修建隧道开挖进尺宜取1.0 m,环向间距宜取0.3 m,小导管长度宜取4.5 m.本结论可为软弱土层隧道设计与施工提供参考.

In order to study the tunnel pre-support measures across the soft soil layer,and based on the eastern Qinghai soft soil tunneling case,the paper adopts the three-dimensional finite element model to simulate the change rule of the surrounding rock stability in pipe sheds,and small pipes with and without pre-support. The study shows that advanced small pipe grouting could meet the requirements of surrounding rock stability and therefore,the small pipes ＇ different diameters,their ring distance,their length,the excavation step length and other support parameters are discussed. The results show that without of grouting,increasing the pipes＇ length and enlarging their diameter and their ring distance cannot restrain the surrounding rock deformation. In the case of the pipe grouting,with the increase of the remaining pipe length,the vault sedimentation value shows a decreasing trend,but there is a limit,that is,there exists a critical length. When the remaining pipe length exceeds the critical length,displacement vault slope becomes more stable gradually. For the construction of tunnels in soft soil,excavation footage should be 1. 0 m,ring spacing,0. 3 m,small pipe length,4.5 m. The conclusion drawn from the paper can provide a reference for the design and construction of similar tunnels.