三台阶核心土环形开挖法在广以隧道中的应用

三台阶核心土环形开挖法是在台阶分部法基础上演变而来的，它集中了台阶法、台阶分部法、上下导坑法等优点。广以隧道地层较老，岩石破碎、节理发育、石质较软，围岩以Ⅳ、Ⅴ及Ⅵ级为主，施工难度极大。文中介绍了三台阶核心土环形开挖法，以及与之相匹配的超前支护、初期支护、防排水及二次衬砌施工等工法。

Three-bench Ring-like Excavation for Core Soil in the Construction of Guangyi Tunnel

The three-bench ring-like excavation for core soil method, developed based on the partial bench excavation, incorporates advantages of bench excavation, partial bench excavation, and top bottom heading excavation methods. The Guangyi Tunnel stands right above some old strata containing shattered, soft rocks and developed divisional planes, where most enclosing rocks are Category Ⅳ, Ⅴ and Ⅵ. Therefore, the construction could be very complicated and challenging. This article mainly introduces the three-bench ring-like excavation for core soil method as well as the supplementary construction techniques such as advanced support, primary support, waterproof ＆ water drainage, secondary lining construction, etc. , hoping to attract more studies and discussions on this subject.