Water Inrush Risk Assessment for a Proposed Karst Tunnel in Complex Plateau-mountain Geological Settings

Water inrush in karst tunnels is characterized by high suddenness, large water volume and severe hazards, and the accurate identification of water abundance and karst hydrogeological conditions is the key to prevention and control. To address the water inrush disaster risk associated with a proposed karst tunnel traversing a complex karst area under the complicated geological conditions of the Yunnan plateau and mountains, this paper systematically investigates the recharge sources, runoff paths and dynamic characteristics of karst tunnel water inrush, and evaluates the risk of water inrush and outburst through integrated field investigations, hydrochemical and hydrogen-oxygen isotope analysis, combined with tunnel water inflow calculations. The results show that: (1)Karst development is most intense in the Maokou and Qixia Formations (P₁m+q) in the study area, exhibiting obvious stratigraphic-controlled, structurally-oriented and hydrodynamic-dependent characteristics. (2) The hydrochemical types in the study area are HCO₃-Ca·Mg type and HCO₃·SO₄-Ca type with high Ca²⁺/Mg²⁺ ratios, reflecting intense karst development. The δD and δ¹⁸O values indicate that groundwater in the area is recharged by precipitation at elevations above 2 000 m. (3) Based on the spatial relationship between the tunnel alignment and the groundwater table, it is recommended to apply different calculation methods to tunnel water inflow for different sections, thereby evaluating the water inrush risk of each section.