Abstract: Tunnel construction often encounters severe deformation and frequent collapse of primary support. Thus, a case study is conducted on the Chazhenliangzi tunnel of the G0615 Jiuzhi-Maerkang expressway. A series of technologies, such as micro-bench excavation, increasing the reserved deformation, double-layer steel frame support, strengthening locking feet, mechanized construction to quickly seal the ring, and strengthening construction management, are adopted to effectively control the large deformation of the surrounding rocks. The research results indicate the following: (1) By strengthening the support parameters in a targeted manner, the primary support deformation can be controlled, effective excavation can be achieved, and the primary support intrusion rate can be reduced from 29% to 0. (2) By reducing the length of the benches, adopting micro-bench, and a single process, the primary support closure time is reduced from 40－50 days to 15－20 days. (3) Due to limited space, some mechanical devices are introduced in a timely manner, and a gantry trolley is used to effectively reduce the erection time and accelerate the construction progress. The minimum monthly excavation footage of a single face is increased from 6 to 36 m.

Key words: highway tunnel, extremely-fractured soft rock, large deformation, mechanism analysis, control technology