Excavation deformation characteristics of underground caverns across fault fracture zone: a case study at Baihetan hydropower station

The right bank plant of Baihetan Hydropower Station has exposed C₄, C₅, and other fault fracture zones (FFZs), thereby increasing rock mass instability. In this paper, the effects of the number and location of FFZ on rock mass deformation were analyzed using field monitoring data. In addition, a validated numerical simulation method was employed to discuss the influence of excavation methods and FFZ properties on rock mass deformation. Results show that as the width of the middle pilot tunnel increases, the top arch deformation initially rises and then falls. Excavating the sidewalls first will significantly aggravate the deformation. As the width or dip-angle of FFZ increases or its height from the top arch decreases, the top arch deformation becomes more significant. The first layer excavation of the plant significantly influences the rock mass deformation. The rock mass located more than twice the width of the tunnel is almost unaffected by FFZ. This study is significant for the stability analysis of deep-buried caverns across FFZ.