Genesis analysis of karst groundwater inrush and prediction of its water inflow in the Huxitai Tunnel

SHAO Changjie; WANG Lei; LIU Huidong; CUI Yongxing; LIU Wei

doi:10.11932/karst20250303

Abstract：Tunnel water inrush is one of the primary threats to tunnel construction safety,not only posing risks during the construction but also creating long-term hidden dangers for the post-construction operation and maintenance.This issue is particularly severe in karst tunnels,where dense karst fractures and conduit networks will lead to rapid water inrush responses to precipitation.Extreme rainfall events can trigger the instantaneous and massive water influxes,making tunnel water inrush in karst regions especially serious.Therefore,it is critical to elucidate the formation mechanisms of tunnel water inrush and to predict water influxes during extreme rainfall conditions in order to address water inrush challenges and ensure safety of tunnel construction in karst regions. The Huxitai Tunnel is examined here as a case study.This tunnel is a critical component of Linjian Expressway,located in the subtropical humid zone of Eastern China,characterized by abundant preciptation and complex geological conditions.The tunnel tranverses through the Carboniferous Huanglong Formation(C2h)and the Chuanshan Formation(C2c)limestones,which features well-developed karst conduits,abundant water,and high permeability.These features result in significant water inrush problems,increased construction challenges,and heightened safety risks.Since the beginning of tunnel construction,water inrush events in varying degrees have occurred in the limestone sections of the tunnel. To investigate the causes of water inrush in the Huxitai Tunnel under karst geological conditions and to estimate its influxes,this study conducted detailed field investigations and in-situ tests to analyze the hydrogeological conditions of the water inrush sections and to determine the groundwater flow systems.Based on the hydrogeochemical characteristics and hydrogen-oxygen isotopes of groundwater,the study analyzed the pathways of karst groundwater flow and the mechanisms of water inrush.It also estimated the contributions of different water sources to the tunnel water inrush by employing the isotopic end-member mixing model.Using precipitation infiltration methods and groundwater dynamics principles,the study calculated groundwater recharge rates and the proportion of tunnel water inrush relative to total recharge,while predicting the maximum water influx in the tunnel during extreme rainfall events.The findings include as follows. (1)According to the pathways of groundwater flow,the tunnel region is divided into three groundwater flow systems:the Caoyuanxi groundwater flow system,the Fenshuijiang karst groundwater flow system,and the Dakengxi-Chaipingli groundwater flow system.The karst water inrush section(K65+100-K65+360)lies within the Fenshuijiang karst groundwater flow system,which consists of the Huanglong Formation and the Chuanshan Formation limestone characterized by intensive karst development,abundant water influx,and high risks. (2)Karst groundwater in the tunnel area is primarily recharged by precipitation,which infiltrates through sinkholes and karst conduits.The hydrochemical characteristics of tunnel water inrush are similar to those of underground river discharge,dominated by carbonate rock dissolution,reflecting a mixture of karst water and sandstone water.Karst water vertically infiltrating from the Huanglong Formation and the Chuanshan Formation limestone accounts for 70％to 79％of tunnel water inrush,with 21％to 30％contributed by lateral sandstone water. (3)During the runoff process,the recharge of groundwater from atmospheric precipitation amounts to 19,324.89 m3·d-1,of which 48.29％is discharged through the tunnel.Under non-extreme rainfall conditions,the predicted water influx into the Huxitai Tunnel is 10,684.89 m3·d-1;however,during extreme rainfall events,the maximum predicted water influx can reach up to 79,364.13 m3·d-1. To sum up,these results provide a quantitative decision-making basis for the prevention and control of water inrush in the Huxitai Tunnel,and also serve as valuable references for similar studies on water inrush of karst tunnel.