Hydrogeological Conditions And Water Gushing Mechanism Of The Buried Deep And Long Tunnel

In the tunnel excavation, we will meet rock burst, weak rock landslides, block stability, the high temperature geothermal heat, gas, water gushing disasters and the environmental effects. The water gushing in the tunnel excavation is more common, if the forecast and actual results varied too big or the prevention and control measures were not reasonable, it will cause significant casualties and economic loss. Because of its long tunnel line, complex geological conditions, big buried depth and high pressure water gushing conditions, it is particularly important to study the hydro-geological conditions and water gushing in the big buried depth tunnel.This paper studies Jinping Ⅱ hydropower station for detailed geology and hydrogeology survey, and makes a brief analysis about the topography, stratigraphic litho-logy and geological structure. The main research is geological conditions including of groundwater types, aquifer group, the chemical characteristics of groundwater and the division of hydro-geological units, and the analysis of source of water gushing and formation mechanism. This paper calculates the water inflow in different address areas through different ways to obtain the more practical results. Basically have the following results:(1) The research groundwater types including of loose rock strata of pore water, carbonate karst fissure of water and bedrock fissure water. For buried long tunnel, it is priority to carbonate karst fissure of water and bedrock fissure water, along with the buried depth of bedrock fissure water increases dominant. The water in the study area PH neutral partial alkaline, groundwater types to HCO3-Ca and HCO3-Ca-Mg primarily.(2) The groundwater supply source including atmosphere of rainfall, surface water melting snow mountains and three categories. Runoff by topography slope influencing control, groundwater in many ways built to discharge, and spring water discharge way there.(3) The study area reveal water gushing section (point) of more than three hundred place through the auxiliary hole in the carbonate strata, formation to T2b primarily. Influence of water gushing happen factors include stratigraphic litho-logy, geological structure, groundwater hydraulics characteristics and the nature of the aquifer, which in deep buried long tunnel construction, the biggest influence with the groundwater hydraulics characteristics.(4) The main easy occurrence water gushing area have the contact belt between carbonate and fee carbonate, fault fracture zone, fracture zone, karst development area and valleys in karst area and dissolution depressions districts.(5) The formation mechanism of the water in tunnel gushing can be divided into the following several kinds:water gushing type hydraulic fracturing, direct type water gushing, blunt water gushing, crushing type through water gushing and fault block water. And for the study area in JinpingⅡ hydropower station obviously are the first three water gushing mechanism, statistics in nearly three hundred water gushing period in auxiliary belong to direct water gushing, in the Zagunao formation is visible blunt water gushing type collapse.(6) To some typical area in auxiliary hole A, we make the theoretical calculation of the yield use the groundwater runoff modulus method, atmospheric rainfall infiltration coefficient method and groundwater dynamic method, and drow the conclusion that different yield results. After analysis shows that the most close to the real yield is the groundwater dynamical method.