破碎千枚岩隧道富水区段施工及支护方法

Construction and Supporting Methods in Rich Water Section of Fracture Phyllite Rock Tunnel

千枚岩岩体具有遇水后软化、膨胀、强度降低等特点,有必要探明岩体软化后围岩的应力与应变特征,探究洞室成形后结构的变形及力学行为,寻求该种地层条件下合理的施工及支护方法。以穿越"5.12"地震发震断裂-龙门山断裂的某千枚岩隧道为背景,首先对干燥及地下水富集区域的洞周变形进行归纳总结,并以此为基础对岩体软化后的物理力学参数进行反演分析,表明了地下水的存在极大弱化了岩体的强度、刚度与抗变形能力;而后,通过将隧道变形及结构受力的计算结果与实测值进行对比分析,进而对施工过程中水对千枚岩软化后隧道结构的安全性及围岩稳定性做出评价。研究表明,对于强震区软岩隧道应结合现场实际情况选择预留变形值25～30 cm,位移控制基准30～35 cm,施工工法应在3台阶+预留核心土(台阶间距为1 m)基础上配合以机械方式开挖为主,微爆破方式为辅,支护则应选择强度及刚度大的结构形式,同时增强超前支护并在施工中重视各环节的工艺衔接可有效避免变形坍塌灾害,提高施工效率。

Since phyllite will be softened, swelling and strength-reduced after absorbing water, it is necessary to investigate the characteristics of stress and strain after the surrounding rock being softened, the deformation and mechanical behaviors of structure after the tunnel formed, and the reasonable methods of construction and supporting for this kind of stratum. Taking a tunnel passing through the Longmenshan fault which experienced the 5. 12 Earthquake as research object, the deformations of the tunnel both in the dry and saturated areas are summarized. Based on these facts, back analysis for physico-mechanical parameters of the softened rock is performed, and the result revels that the strength , stiffness and anti-deformation capacity of the rock are reduced by the underground water. Then, after comparing the numerical result of deformation and internal force with the measured values in field and analyzing the differences, the effect of water on the stability and safety of the tunnel affected by softened phyllite during the construction is evaluated. It reveals that in order to avoid large deformation and even collapse, and to improve the efficiency of construction, several measures can be taken such as reserving the deformation allowance of 25 -30 cm for the tunnel built in intense seismic area, controlling the deformation value within 30 - 35 cm, adopting the method of 3-bench excavation with core soil （1 m interval between benches） while excavating by machines and supplementing by blasting, choosing high-strength and large-stiffness structure for supporting, strengthening the advance support andemphasizing the mutual connection between different construction techniques.