Characteristics of the karst water system on the northeast wing of the Huangling anticline and its impact on water diversion tunnel engineering

The strata in the northeast wing of the Huangling anticline consist of interbedded carbonate rocks and clastic rocks. As the carbonate rocks underwent strong karstification, karst water inrush would be a significant factor impacting the construction of underground engineering in this area. Taking the Huangling anticline section of a critical national water diversion project as the research object, the characteristics of the karst groundwater system and the water inrush conditions in tunnels were identified by various methods, such as karst hydrogeological surveys, tracer tests and hydrogeochemistry analysis. These results show that the aquifer system contains four sub-aqueous systems with a structure of strong and weak permeable interlayers in the vertical direction, in which a multi-stage karst groundwater system has developed with shallow rapid circulation, intermediate rapid circulation and a deep slow circulation subflow systems. The faults constitute the vertical channels for hydraulic exchange between sub-aquifer systems. The water diversion tunnel primarily crosses the deep Dengying Formation (Z2dn) and Tianheban-Shilongdong Formation(∈1t+sl) aquifer systems with weak karst development. However, a large-scale high-pressure water inrush accident may occur when passing through the Dianya fault, which may transfer groundwater from the upper karst sub-aquifer system of the Loushanguan Formation-Nanjinguan Formation (∈3l-O1n) into the tunnel. The risk of encountering conduit water inrush accidents is high during construction when the construction branch tunnel passes through the discharge area of the Bailongdong groundwater flow system in the ∈3l-O1n sub-aquifer systems. The accuracy of identifying of karst groundwater flow system features and inrush conditions can be improved by joint interpretation of multiple hydrogeological methods.