富水糜棱岩大断面隧道Ⅵ级围岩变形控制技术

Deformation Control for a Large Section Tunnel in Water-Rich Mylonite with Grade Ⅵ

改建的成昆铁路秀宁隧道出口段(510 m)通过罗茨-易门大断裂,并下穿龙潭水库,隧道围岩为罕见的富水糜棱岩,围岩级别为VI级;富水糜棱岩开挖后呈流塑状,极易产生涌泥和溜坍,导致初期支护产生大变形。文章基于糜棱岩抗剪强度的水稳性试验研究,针对该段隧道工程提出了采用全断面超前预注浆并辅以大管棚控制围岩变形的支护方法,以及三台阶七步开挖法进行了数值模拟分析。分析结果与围岩变形监测结果均表明,全断面超前注浆可以有效堵水和挤水,实现富水糜棱岩地层的排水固结,提高围岩强度;大管棚超前支护及大拱脚三台阶七步开挖法可以有效控制围岩变形,保证施工安全。

The exit section （510 m） of the Xiuning tunnel on the rebuilt Chengdu-Kunming railway, passing under the Longtan reservoir, is located in the Luoci-Yimen fault zone. The stratum is composed of rare water-rich mylonite with a classification of grade Ⅵ. After excavation, mylonite in the form of plastic flow can easily cause mud gushing and collapse, resulting in large deformation of the primary lining. To pass through this stratum safely and quickly, the deformation of the surrounding rock has to be controlled. Based on a water stability test of mylonite shear strength, this paper presents a support method for this section, namely, full-face pre-grouting with pipe-roof support. Using numerical simulation and deformation monitoring of the surrounding rock and lining structure, it was proven that full-face pre-grouting can effectively achieve water blocking, water squeezing, drainage consolidation and rock strength improvement; pipe-roof pre-support and three-bench seven-step excavation can effectively control rock deformation, ensuring construction safety.