Fault-controlled damage localization and layout selection for deep underground cavern complexes under high in situ stress: a coupled continuum–discontinuum case study of the Yebatan Hydropower Station

Deep underground cavern complexes in high-relief terrain often face high in situ stress and persistent faults, where excavation-induced damage is governed by coupled stress magnitude, fault architecture, and cavern arrangement rather than geometry alone. How this coupling organizes damage spatially and should guide layout selection remains unclear. Using the Yebatan Hydropower Station (southwest China), where a deeply buried granodioritic rock mass is cut by major faults under a maximum principal stress of 37.57 MPa, this study compares cylindrical and corridor-shaped tailrace surge-chamber layouts through integrated geological characterization, triaxial testing, three-dimensional stress reconstruction, FLAC3D continuum modeling with support, and unsupported 3DEC block analysis. Compressive stress concentration is nearly identical between layouts. The corridor-shaped scheme increases tensile- and plastic-zone volumes by 14.8% and 50.0%, respectively, but reduces large-deformation volume by 11.7% and weakens the adverse interaction with the dominant fault. Additional yielding is confined to surge-chamber sidewalls, while primary caverns remain comparable; block-instability volumes are similar, but the corridor layout concentrates unstable blocks into fewer, more accessible sectors. Damage location, concentration, and reinforcement accessibility—rather than aggregate adverse-zone volume—are thus more diagnostic for layout selection, offering a transferable framework for high-stress, faulted rock masses.