Abstract:  To address the problems of unstable support and surrounding rock, long deformation time, and frequent design changes in the construction process of soft rock tunnel with high geostress, the successful cases of large deformation control measures of soft rock tunnel with high geostress in China and abroad are analyzed, and the geostress and geological environment of the tunnel as well as the corresponding construction methods and support forms are summarized. Additionally, the safe, economical, and effective control measures for high geostress soft rock tunnel are proposed, and the above research results are analyzed and verified by practical engineering. The results show the following: (1) The rock mass of Ningchan tunnel is extremely broken, the rock strength is low, and the main causes for large deformation of surrounding rock are extremely high geostress, formation lithology, joint, and softening interlayer, rock occurrence and dip angle, and human factors. (2) The strength stress ratio and relative deformation are used to classify the large deformation of the soft rock tunnel with high geostress in combination with the geological structure, and the fivelevel classification scheme is more reasonable and accurate. (3) The deformation control concept of "antiyield combination, moderate flexibility, and common load" and the combination of presupport, support, reserved deformation, and construction methods can effectively control the large deformation of the tunnel.

Key words:

tunnel engineering, high geostress, large deformation of soft rock, surrounding rock classification, deformation control