| In the soluble-rock area,tunnel construction has great influence on dynamics of groundwater.Tunnel excavation will result in rapid discharge of groundwater stored in mountain body.Then regional groundwater level decreases fast,forming a range of precipitation funnel and capturing karst springs flow.Those above seriously damage regional ecological environment.Especially in southwestern China,the geological structure is complicated with developed fold structure.Under the influence of topography,geological structure and the spatial morphology of aquifer,the groundwater circulation condition is fairly complex.Hence,constraining the groundwater circulation is significant for construction in the fold area.Using the water-balance analysis of regional groundwater dynamic is characterized by simple calculation logic and accurate calculation results that are close to reality.However,previous studies were mainly concentrated on the inflow forecast of tunnel water,whereas less attention has been paid to the analysis study area groundwater circulation by water-balance analysis.The Chongqing-Kunming railway is the main railway line in the southwest region,connected to the north China and northeast China with the west Chongqing high-speed railway.The construction of the Yujiawan tunnel is across the Datianba syncline and has a great influence on the regional groundwater dynamics.In this paper,the Datianba syncline was chosen to be divided the hydrological units,based on the the groundwater recharge and drainage conditions.According to the principle of water balance,the atmospheric rainfall area was calculated by known excretion.The calculated results were compared with divided unit area,which is helpful to verify the feasibility of the cell line.Hence,groundwater circulation in syncline can be judged.Using the water balance method to calculate the tunnel water inflow in different conditions,compared with the hydrodynamics method,the feasibility of water balance theory is applied to the analysis in the study area,the specific research contents and conclusions are listed as follows:(1)The karst water circulates only in the inner of syncline under the action of the upper and lower non-soluble rocks.Cut by Guan,Baishui,and Junlian Rivers,the Datianba syncline is divided into three excretory systems which have equivalent drainage datum plane.The two-wing karst water is recharged by the precipitation,then flows along strata,and finally discharges as karst spring or underground river.In the area where the dissolution fracture is poorly developed,the groundwater runoff channel is narrow and the groundwater system cannot be formed.The groundwater runoff is directly excreted in the surface water system after being cut by gully.According to three drainage system of the Guan,Baishui,Junlian river,combined with the regional watershed,physical water-resisting layer surface,the study area is divided into Guan river unit(?),Baishui river unit(?),Junlian river unit(?)three level of hydrogeological unit.(2)The research area is in equilibrium under natural conditions.According to the principle of water balance,the recharge area of atmospheric precipitation is calculated using groundwater excretion.The recharge area required by the calculation results of the Guanghe hydrogeological unit is 14.796km~2,and the error of 14.410 km~2 is2.7%.The recharge area of Baishui unit is 15.593 km~2,and the error of 15.861km~2 is1.7%.The recharge area required for the unit is 18.054 km~2,with an error of18.822km~2 and an error of 4.1%.Due to the fact that the quantity of recharge is not strictly comparable to the excretion,it is considered that the calculation error is feasible within the allowable range.(3)According to the results of the water balance calculation,a hydrologic year each unit quantity of atmospheric precipitation to meet excretion,karst water doesn't need other recharge sources.Datianba syncline does not present around-axle groundwater flow model.Datianba syncline is formed by axisymmetric syncline of soluble and non-soluble strata.The core of soluble strata is covered by thickened non-soluble strata.The interaction between groundwater and outside environment is weak and the karst is not developed.The slanted flanks can be dissolved,the karst development is strong under the action of atmospheric precipitation,and the groundwater runoff is fast,forming the water enrichment of the flank.In this hydraulic condition,the karst water precipitation in two wings,along the tilt direction of water-resisting layer to the nuclear runoff,but as a result of deep water permeability,karst water turned along the strike runoff,finally a discharge of the drainage channels in crosscutting the strike of the strata.Therefore,the Datianba syncline is a closed-directional single-wing longitudinal circulation model.(4)According to the relationship between the influence radius of the tunnel and the inlet section and the distance between the tunnel and the karst spring,the water inflow under different conditions is calculated.In combination with the simulation results and the actual engineering situation,it was found that when the impact radius of precipitation did not reach the spring,the normal inflow was 8732.96 m~3/d in the tunnel entrance section,and the maximum inflow was 15598.64 m~3/d.The outlet section of the tunnel has a normal inflow of 5512.35m~3/d and the maximum inflow is9846.06 m~3/d.(5)The water dynamic method is used to calculate the normal inflow and maximum inflow of tunnel entrance and exit.The normal flow rate of the tunnel inlet is 8851 m3/d,and the normal flow rate of the outlet is 5566 m~3/d.The maximum inflow of the tunnel inlet is 16577 m~3/d and the maximum inflow of the outlet is10822 m~3/d.The result of calculation is close to the result of the water balance method,so it is feasible to predict the inflow of the large field dam to the slanting Yujiawan tunnel by the principle of water balance. |
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