Abstract: To optimize the stress of support structure and control surrounding rock deformation of soft rock tunnel with high insitu stress, the hole type and supporting time of doublelayer primary support are examined. First, the supporting effect of single and doublelayer primary support and surrounding rock deformation law of soft rock tunnels with high insitu stress are analyzed based on onsite monitoring data. Then, FLAC3D software is used to compare and analyze the force and deformation of the tunnel under three kinds of hole types, such as horseshoe (heightspan ratio of 0.80), quasicircular (heightspan ratio of 0.90), and circular (heightspan ratio of 1.00), and the tunnel force and deformation conditions after applying second primary support when the deformations of the first primary support reach 300, 350, and 400 mm. The results are as follows: (1) As for the twolane tunnel in grade Ⅲ surrounding rock with high insitu stress, the doublelayer primary support can effectively control the surrounding rock deformation better than the singlelayer one, but the phenomena of arch shoulder failure and inverted arch cracking still occur. (2) Appropriate increase in tunnel depthspan ratio can effectively reduce the deformation of surrounding rock and supporting structure. The effect reaches the highest when the heightspan ratio is 1.00. (3) Appropriate increase in reserved deformation space in the first layer of primary support and delay of the second primary support will cause a great reduction of supporting stress, so it is recommended to apply the second primary support when the deformation of the first primary support reaches 400 mm.

Key words:  , high insitu stress, large deformation soft rock tunnel, hole type, tunnel heightspan ratio, doublelayer primary support, supporting time