Abstract: The coupling effect between high geostress state and low strength surrounding rock increases the risk of tunnel instability. In order to effectively control the large deformation of soft rock tunnels with high geostress, the construction experience of nearly ten tunnels in soft rock with high geostress in LijiangShangriLa, YuxiMohan, and ChengduLanzhou railways are summarized, the deformation characteristics and key control technologies of these large deformation tunnels are expounded, and the effectiveness of relevant technologies with monitoring data is rerified. The following conclusions are made. (1)The reserved deformation is an important basis to avoid the primary support from intruding into the structural limit of the tunnel after a large surrounding rock deformation. (2) For the singletrack tunnel with a dominant horizontal tectonic stress, increasing the curvature of the sidewall can effectively control the convergence of the sidewall. (3) The doublelayer primary support together with mixlength bolts can increase the stiffness of the primary support and reduce the surrounding rock deformation. (4) The large deformation can be controlled effectively and the cracking of secondary lining can be reduced by installing the second lining at a proper time. (5) Quick closing of the invert of the primary lining and keeping the distance between the invert and the tunnel face at less than 20 m can play an effective role in inhibiting convergence.

Key words: soft rock tunnel, high geostress, large deformation; deformation control, reserved deformation, sidewall curvature, doublelayer primary support