Study On Seepage Field And Water Inrush Forecast Of Fuge Village Tunnel Site

Recent years have witnessed rapidly expanding economy.The railway transportation infrastructure construction project plays an important part and even serves as a pillar for the economy of various countries.As China has its economy and technology enhanced in the past30 years,it is now proactively supporting other developing countries in terms of major infrastructure projects.For instance,the Mowan Railway of China-Laos Railway,crossing the fault suture zone of the Mekong River Basin in Luang Prabang,was built with China playing the leading role.However,rock fragmentation,severe weathering and sufficient rainfall in the section where the tunnel passes hinder the construction.Moreover,designers and builders of tunnel projects have always been plagued by water inrush during construction.Thus,research on the regional seepage field and water inflow prediction is urgently required.Characteristics of the seepage field,hydrochemistry,regional supplement,runoff and draining as well as influencing factors of water inflow of the tunnel site are analyzed in this paper with Fuge Village Tunnel in the Luang Prabang Fault Fracture Zone of the China-Laos Railway as the research object based on relevant literatures and documents on local hydrology,drilling,meteorology and geological exploration.Furthermore,sections where water inrush is most likely to occur in the tunnel and the water inflow are analyzed and predicted in this paper by simulating conditions of the three-dimensional seepage field under different working conditions via the FEFLOW numerical simulation software for the sake of deep buried tunnel engineering in fault suture zone.Conclusions are as follows.（1）The regional groundwater,bedrock fissure water according to strata analysis,is the type of HCO₃-Ca with a circulation path that is not deep and water-rock interaction that is not obvious in light of hadrochemical analysis of the water sample.Moreover,the aquifer where the tunnel passes through is phreatic.Accordingly,the regional replenishment comes from atmospheric precipitation with the runoff characterized by shallow and surface circulation and the drainage path surrounded by valleys and rivers.Therefore,the probability of tunnel passing through the hydrogeological unit V where water inrush occurs is the greatest.（2）The numerical simulation of natural conditions shows that the tunnel at the fault will not have water inrush due to the water head decrease;and the water supply of the groundwater in the southern part of the tunnel site is greater than that in the northern part of the tunnel site.The groundwater runoff,mainly longitudinally,in the northwest of the tunnel site heads towards northwest,while that in the southeast,mainly horizontally,heads towards the southeast low-lying area,leading to shallower circulation depth of the groundwater and greater elevation of the surface water than that of the northwest.（3）The maximum groundwater level in the rainy season can reach 1168m.Although the terrain of the southern section of the southeast tunnel site is steeper than that of the northeastern section,the regularity of groundwater runoff is not as good as that of the northwest due to its lithological restrictions.It is speculated that the probability of water inrush in D2K123+500～D2K124+000 during tunnel excavation is the greatest considering the overall influence of pore water pressure,structure and lithology.（4）The maximum water inflow predicted relatively accurately as 97278 m³/d via the Oshima Hiroshi formula can guide the tunnel construction.The average value of normal water inflow as 63514 m³/d via the hydrogeological analogy method,the railway empirical formula,the precipitation infiltration method and the Koskakov formula can guide the tunnel construction.