Excavation-induced deformation and stress responses of a highway tunnel in fault fracture rock zone with high geo-stress: a case study of Xiangjunshan tunnel

Tunnel excavation in high geo-stress shattered fault zone usually causes lining cracking, tunnel collapse and arch settlement because of rock fragmentation, low strength and poor stability of surrounding rock. This paper takes Xiangjunshan tunnel in high in-situ stress fault fracture zone in Sanmenxia, China, as an example. The field monitoring tests included surrounding rock deformation monitoring, surrounding rock-initial support, shotcrete, steel arch and primary support-secondary lining stress measurement. These tests were utilized to study the deformation law and stress response of six sections in Class IV and V rock mass during the tunnel construction. Test results showed that the tunnel deformation of fault fracture zone was asymmetrical during excavation. The surrounding rock stress presented a discrete distribution in space, the stress variation trend of shotcrete and steel frame was not coordinated. The stress of shotcrete reached 75% of its peak value in the initial stage, while the stress of steel frame reached its peak value in about 1 month. The temporal distribution curve of primary support-secondary lining stress indicated three stages of intense growth, quick development and steady development stage in the construction. The research results give significant insights and guidelines for tunnel construction in similar geological conditions.