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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 its special forming process, granite alteration zone changes its physical and mechanical properties significantly, and geological disasters are prone to occur when there is tunnel crossing. When the Ping tunnel passes through the shallow contact alteration zone between granite and sandstone, the entire subsidence of the leading pilot tunnel occurs suddenly with the supporting structure intact, resulting in the instantaneous vault settlement amount reaching 1.5m. Through the analysis of engineering geological features, monitoring and testing of rock mass and soil, it is clear that the disasters occurred at the alteration zone of granite and sandstone. The alteration not only produced a large amount of hydrophilic soft rock minerals, resulting in extremely low rock mass strength, But also lead to loose and broken rock mass. The large deformation caused by disturbance and stress adjustment of tunnel excavation. Through a series of measures such as drainage, reinforcement of surrounding rock and reinforcement of initial support, tunnel excavation successfully passed the alteration zone to ensure the safety of the project. Its construction experience can be used for reference for similar projects.