Abstract: A case study is conducted on the Dongmachang No. 1 tunnel of the Huali expressway crossing the ChenghaiBinchuan active fault to address the issues of support deformation, cracking, and destruction during tunnel construction in areas with active fractures. A high amount and rate of uneven destruction with a long duration and difficulty in achieving convergence are observed for the deformation of the primary support of the tunnel during the construction. Because of the influence of the Chenghai fault, the geological tectonic stress level(considering the horizontal tectonic stress as the main stress) in the tunnel site is high, and the section affected by the fault exceeds 2 km in length. Using the analytical results of the monitored data and test results, a comprehensive support system using a combination of long and short supports, active control, layered supports, timely ring close, and reserved inner space is proposed based on the deformation, cracks, and destruction conditions of the tunnel support in the excavated section. The analytical results of the monitoring data show the following: (1) The average cumulative settlement and average cumulative convergence after implementing the optimized plan are, respectively, 12.46% and 26.57% higher than the values before plan optimization; this result is attributed to the long operation time before optimization. (2) After the implementation of the optimized plan, the surrounding rock deformation is mainly concentrated in the first primary support layer stage, where the generated deformation accounts for approximately 70% of the total deformation; After the implementation of the second primary support layer and the inverted arch, the deformation rate decreases drastically and is within 0.8~1 mm/d before the secondary lining pouring.

Key words:  tunnel engineering, high geostress, active fracture, softrock; large deformation, support system