Controlling effect of the karst hydrogeological structure on karst collapse: a case study of the Chaoyang Tunnel, Guizhou

This study investigates karst collapse induced by water inflow in the Chaoyang Tunnel, Guizhou Province. Through field investigations and tracer tests, the study ascertains the hydrogeological characteristics of the tunnel and its surrounding terrain, analyzing the impact of sudden water inflow in karst tunnels on the development of surface collapse. The following findings include: (1) confirmed direct hydraulic connectivity between the tunnel and the Dongdiu collapse zone, with abrupt water inrush causing rapid groundwater decline and altering hydrodynamic conditions in karst conduits; (2) multi-peak tracer curves reveales complex internal conduit networks and localised water storage structures, providing new insights into subsurface flow paths; (3) karst strata and fault structures serve as the primary internal controls on collapse development, while extreme rainfall acts as a major external driver that accelerates overburden erosion through rapid groundwater fluctuations, linear conduit-induced hydraulic scouring, and cyclic desiccation-saturation under dual water table disparitie; (4) the collapses can be classified as a drainage-precipitation type governed by subsurface erosion. The study innovatively combines tracer tests and hydrogeological modeling to quantify conduit structures and their role in collapse initiation, providing a predictive framework for karst tunnel hazards.