Theoretical Study And Application Of Water Lowering Design In Opencast Mine Engineering

Groundwater draining is one of the critical problems which is interrelated to success or failure of foundation pit engineering and opencast mine exploitation. J Drpuit formula is used commonly, that is suited to water lowering design of single-well or group-well when aquifer structure and boundary is simple. At present, it has been adopted in water lowering of foundation pit engineering, opencast mine exploitation, subway construction and soil tunnel construction.On the side, how to fix on hydrogeology parameter in calculation is another difficulties, such as, determination principle of dewater well depth, determination of influence radius, determination of permeability coefficient k etc.Numerical simulation technology emerges as the method exist difficulty in complex boundary and complex hydrogeology condition, which is widely applied by water lowering and structure and lowering and settlement.The most advantage of numerical simulation technology is that complex hydrogeology condition model which is inhomogenous and non-uniform thickness can be depicted accurately.Whether traditional big well method or numerical simulation, people pay attention to water lowering design and building hydrogeology condition model, but few study of water lowering effect theory has been done, only limited to practical observation(mainly on settlement). The aim has not been achieved yet, that the practice corrects the theory and then the theory is applied in optimizing design of the practice and the information.Part one, hydrogeology condition of mineral area is discussed detailedly, and the hydrogeology conceptual model is summarized. Based on water-bearing characteristics, suitable numerical model should be selected, and each divisional hydrogeology parameter is determined through observed data. Based on application environment of visual MODFLOW soft, the boundary is summarized reasonably, and then a quasi 3d flowing numerical simulation model of groundwater is established. The research range of local water lowering model is 920m×860m×80m, and the model is divided into 20m×20m cell grid in the plane, total 1978; It can be divided into 4 layers according to formation lithology, total 7912 grids in the vertical direction.The hydrogeology parameter of mineral area is determined and the model has been validated through mass data of water level observation and mining yield from 2005.4.25 to 2005.10.9.Part two, based on the verified numerical model, the calculation range of the model is 3000m×3000m×80m, and the second kind flow boundary is delineated. Forecast of water lowering draining, pump water time, the amount of wells, arrange of wells, pumpage and the result of construction simulation have been done. From above four simulating calculation methods we can see that each that pump water time, the amount of well, arrange of well and pumpage have their own founction. Combined with numerical simulation, the law of improve water lowering construction efficiency has been given. According to numerical simulation calculation, forecasting results of groundwater draining has been got. Uninterrupted draining, 47 water lowering wells are required from 2005.4 to 2005.9, in Winter, however, another 60 wells with 160m3/d pumpage are needed. Thus nearly 110 wells continue pumping for 3 months that is by the end of 2005, when it can reach the design drawdown.Part three, based on theoretical study, it is applied to foundation pit water lowering engineering in Shenyang subway No 1 line. According to hydrogeology investigation and pumping test results of engineering region, reasonable seepage calculation model has been established using Visual Modflow program. According to hydrogeology condition, hydrogeology test parameters and foundation buried depth, and under the premise of standard requirements, the water lowering scheme of foundation pit construction has been studied, and then the way of"density well spacing, little pumpage"is determined. Based on the Modflow of physical model and foundation pit dewatering scheme, the drawdown simulation should be done around selected fields, and the change of seepage fields has been forecasted in field region and its peripheral.