Abstract: Soft rock large deformation occurred in East Tianshan extralong highway tunnel crossing F2 fault fracture zone. Accordingly, the theoretical analysis, numerical simulation, onsite monitoring, and statistical analysis are employed to investigate the control standards of primary support deformation of tunnel constructed by twobench reserved core soil method and threebench method. Then the phased early warning method of primary support deformation is proposed. The results reveal the following: (1) The reserved deformation of East Tianshan tunnel crossing F2 fault fracture zone is recommended to be 60~80 cm, which can meet the construction requirements. (2) The primary support deformations induced by top heading and lower bench excavation using twobench reserved core soil method are recommended to be 60% and 40% in total deformation, respectively, whereas those induced by top heading, middle bench, and lower bench excavation using threebench method are recommended to be 20%, 65%, and 15% in total deformation, respectively. (3) Grades Ⅰ, Ⅱ, and Ⅲ early warning should be started respectively when the primary support deformation not exceed reserved deformation, exceeds the reserved deformation but not exceed 5% of the secondary lining design thickness, and not exceed 10% of the secondary lining design thickness. Normal construction can be operated in case of grade Ⅰ early warning, treatment measures such as controlling excavation advance and bench length, setting up retaining arch in time, and closing primary support as soon as possible shall be undertaken in case of grade Ⅱ early warning, and short bench or micro bench method shall be further used in case of grade Ⅲ early warning.

Key words: highway tunnel, fault fracture zone, soft rock large deformation, reserved deformation, primary support, control standards, early warning of deformation