Forecast And Analysis Of The Hydro-Geological Framework Characteristic Contributed Water Inflow Of Nibashan Tunnel

In this paper, the topography, meteorological and hydrological conditions, rock characteristics, geological structures, and weathering and unloading conditions of the tunnel area are introduced detailedly according to the field investigation. Then, The hydrogeological significance of the lithology and structure and the permeability characteristics of the aqueous medium of the tunnel area are also analyzed with the permeability of the hydrogeological structure system of the tunnel area analyzed. After that, a seepage model of the tunnel area is built by the thermal analysis module of the Ansys software to simulate the water yield of tunnel. Finally, by combining with the water balance method and fuzzy mathematics, a comprehensive evaluation of tunnel water inflow is conducted to compare with the field test data. Conclusions are as follows:(1) The aqueous medium of the tunnel area can be divided into different types such as diagenetic fissures, diagenetic pores, tectonic faults, karst rooms, loose accumulation layer pores and weathering and unloading fissures, which have different permeability characteristics in different distributions.(2) The running of the underground water of the whole tunnel area presents the characteristics of multiple layers, multiple mediums and multiple flow directions in plane and vertical, which makes the hydraulic connection strength between units presents different levels. Considering the poor permeability of the fractured non-carbonate rock mass under the shallow layer of the tunnel area, which has a poorer permeability as the joint gets closer when the tunnel gets deeper, and the good permeability of the fault zone, the fault zone can be regarded as conducting layer and the non-fault development area of the fractured rock masses as aquifuge. Based on the detailed study of the recharge and discharge conditions and the geochemical characteristics of the groundwater in the tunnel area, the distribution of the underground water of the tunnel area is divided into five basic hydrological units:the shallow underground water unit near the inlet end, the shallow underground water unit near the outlet end, the deep underground water unit near the inlet end, the deep underground water unit near the outlet end, and the deeper underground water unit near the outlet end.According to the stress field test data, the maximum water inflow value is130000m3/d. And the predictive steady water inflow value by the comprehensive evaluation is86531m3/d. Without considering the hydro-geological framework characteristic, the atmospheric precipitation infiltration coefficient method, groundwater runoff simulation, groundwater dynamics method give us a maximum water inflow value of only48252.7m3/d. So, the method in this paper is closer to the field conditions, and the result could meet the basic needs of the project.