Abstract: Primary support deformation, inverted arch uplift, and secondary lining collapse often occur during soft rock tunnel construction with high ground stress. Therefore, countermeasures for large deformation of the Daliangshan tunnel of the YunxianLincang expressway are discussed. The deformation is characterized by follows: (1) large cumulative deformation amount, high deformation rate, and long duration of primary support deformation; (2) long section of uplift, and large uplift difference of inverted arch greatly affected by water; (3) sudden crushing crack damage on arch shoulder and crown after several months of secondary lining. The geological conditions, failure characteristics, deformation characteristics, and supplementary survey conclusions of the soft rock large deformation section of the Daliangshan tunnel are comprehensively analyzed using theoretical analysis, engineering analogy, numerical simulation, and onsite measurement methods. A plan for large deformation treatment, including optimization of inverted arch curvature, primary support of doublelayer steel frame, secondary lining reinforcement, and limiting anchor bolts around the tunnel, is designed, and construction and research on the experimental section are conducted. The experimental results reveal the following: (1) The cumulative construction of the experimental section is 323 m with an average monthly footage of approximately 43 m. (2) Compared with the original design, the support scheme for the experimental section reduces the maximum peripheral convergence of the primary support from 1.4 to 0.30 m, the maximum arch settlement from 0.80 to 0.52 m, and the daily average deformation amount from 7 to 1－2 cm. (3) The large deformation of the tunnel has been effectively controlled, with no cracking or falling of the primary support, and no damage to the inverted arch and secondary lining. (4) Based on monitoring data and onsite conditions, the comprehensive support system scheme for the experimental section is analyzed and summarized to be reasonable, and the key technologies for large deformation treatment are generally successful.

Key words:  , tunnel engineering, high ground stress, soft rock, large deformation, support system