Abstract: Due to its softening and creep when the groundwater is encountered, the large deformation of tunnel in the soft rock mass is frequently occurred in the tunnel construction worldwide. This paper presents a case history of investigating the cracks in the secondary lining at the portal of Huangjiazhai Tunnel in Mazhu Expressway. The engineering characteristic of the soft rock mass, such as, type of surrounding rock mass, structure, strength and stress-strain property and the groundwater were evaluated. The probable factors that resulted in the cracking in the secondary lining were analyzed. Brocken, soft rock mass, groundwater sensitive and strong creep under stress are the major reasons. The mitigation scheme utilized the radial grouting from the perforated sleeve pipes for the entire cross section. Increasing the supporting and initial excavation and creating permanent drainage holes were also used in the mitigation system.

Key words: Highway Tunnel, Secondary Lining, Cracking, Back Analysis, Mitigation Measures