安坪隧道穿越花岗岩蚀变带的大变形机理和治理措施

Mechanism of Large Deformation and Control Measure of Anping Tunnel in Granite Alteration Zone

花岗岩蚀变带由于其特殊的形成过程,使其物理力学性质发生显著地改变,当有隧道穿越时极易发生地质灾害。安坪隧道穿过花岗岩与砂岩的浅埋接触蚀变带时,在支护结构完好的情况下超前导洞突然发生整体沉陷,造成瞬时拱顶沉降量达到1.5m。通过工程地质特征分析、监控量测和岩土体的试验研究,明确灾害发生在花岗岩与砂岩的蚀变带处,蚀变作用不但生成大量亲水性软岩矿物,致使岩体强度极低,而且导致岩体松散、破碎;隧道开挖的扰动和应力调整触发了大变形。通过排水、加固围岩和增强初期支护等一系列治理措施,隧道开挖顺利通过了蚀变带,确保了工程安全。其施工经验可供类似工程参考借鉴。

Due to the special formation process of the granite alteration zone, its physical and mechanical properties change significantly, and geological disasters are prone to occur when a tunnel passes through it. As Anping Tunnel passes through the shallow early Yanshan granite and sandstone contact eroded belt, there is a sudden whole tunnel subsidence of the pilot heading under the intact supporting structure, and cause the vault instantaneous settlement reaching 1.5m. The alteration zone of the granite and sandstone is become known by engineering geological characteristics analysis, monitoring and measuring and experimental studies of rock and soil, and the alteration not only generates a lot of hydrophilic soft rock minerals, resulting in the low rock strength, and leads to loose rock and crushing; the disturbances of tunnel excavation and stress adjustment triggered large deformation. To ensure the tunnel excavation pass the alteration zone without troubles and the safety of the project, a series of control measures, such as drainage, reinforcement of surrounding rock and enhancement of initial support have been taken. Its construction experience can provide reference for similar projects.