| Lithology of red bed in Yunnan area is given priority to mudstone and sandstone formation, and form the alternating layers of rock group with them, and become the good storage and transport channel of groundwater. K1g assise for red bed in Yunnan is the richest aquifer, may constitute a centralized water supply source. At the same time, tunnel crossing in the red bed water storage structure must have a significant impact on the environment, and may produce larger water inflow. Given this, in this paper, taking Fengtun tunnel of diversion project in Yunnan for example, using Visual Modflow simulate the water inflow when tunnel crossing the storage structure of red bed and the change of seepage field along the construction process, In order to provide the basis for the Fengtun tunnel groundwater environmental impact assessment.According to the geological environment conditions of fengtun tunnel, analyze the water-storage structure and hydrogeological unit in research area. On this basis, according to tunnel through the different segmentation of hydrogeological units, preliminary study the process of tunnel water gushing, and according to the characteristics of process of tunnel water gushing, construct a three dimensional numerical model of fengtun tunnel to simulate tunnel gushing process.The main research results of this paper are as follows:Oriented folds are nearly north-south in study area, From west to east, consecutive double fold area is formed as Liujiacun syncline, Shaoxiangtai anticline, Tasizha syncline, Fengtun dome Hydrogeological unit(Ⅱ) of Sijiaodi is constituted by the K1g aquifer, and have the characteristic of deep runoff and shallow circulating, especially the deep runoff has particularity characteristic:large scope of supply, runoff way is long, and the discharge is concentrated.For the study area storage structure and process water gushing through the tunnel characteristics of each segment K1g aquifer, build natural seepage field model:using "cut section" and "Add layer" approach to characterize the sandstone and mudstone interbedded; determine K1g aquifer permeability tensor field of statistics through cracks and water pressure test results according to their correction; choose rivers and surface watershed boundaries as a model; establish hydrogeological zone water balance equation to obtain the study area infiltration coefficient (a). In the tunnel construction process, using the whole row blocking drainage and construction methods combined, the two conditions simulated tunnel through the process Klg gushing aquifer segment.In the whole drainage conditions, when Tunnel through the core of the Tasizha anticline turning end, the water inflow was14443.73m3/d, the impact on the core of the anticline groundwater is very big, affecting a radius of about700m,and Syncline East Wing have a significant drop-bit funnel; When tunnel construction to the east wing of Shaoxiangtai syncline, water inflow to12445.66m3/d, groundwater levels continue to decline, affecting the stability radius of1.75km, and because the synclinal flanks groundwater hydraulic gradient decreases, water inflow to the West Wing11763.25m3/d significantly reduced.Block row combination condition, when Tunnel through the core of the Tasizha anticline turning end, Anticline groundwater seepage field change is small, syncline east wing appears weak drop-bit funnel; When tunnel construct to the east wing of Shaoxiangtai syncline, Tasizha anticline groundwater levels rebounded, syncline east wing tunnel water inflow as13692.46m3/d, compared with the whole drainage conditions increased significantly.On the impact of the weaker red layer permeability of the study area, groundwater circulation is slow, groundwater seepage field changes generated during tunnel construction with a certain lag, so it is difficult to recover in a short time natural state after the closure of groundwater seepage field. |
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