MODELS FOR OPEN PIT MINE DEWATERING

A new analytical model has been developed to analyze the relationship between system discharge and drawdown for open pit mine dewatering problems in aquifer systems under confined, unconfined, and leaky aquifer conditions. The model is developed by using the Cooper-Jacob approximation of the Theis well function and the principle of superposition for multiple well systems in a homogeneous confined aquifer, by using the steady-state approach of the Hantush method and the principle of superposition for multiple well systems in a homogeneous steady-state leaky aquifer, and by using the Cooper-Jacob approximation, the principle of superposition for multiple well systems, and the Girinski potential theory in an unconfined stratified aquifer.;The analytical model is capable of handling various pumping schemes and spatial arrangements of the well row systems for open pit mine dewatering. The model is used to construct the system discharge vs. drawdown curves for a designed dewatering system in homogeneous confined aquifer and homogeneous unconfined aquifer systems under a wide range of transmissivities and hydraulic conductivities, respectively. Those curves can be used as a guideline in the early stage of design and planning under a specific dewatering geometries for a potential open pit mine.;A three dimensional finite difference model developed by Trescott was adapted and modified to simulate the open pit mine dewatering in complex aquifer systems. The numerical model also served as a calibration and testing tool for the analytical model. Through simulation and parametric analysis both the analytical and numerical models have been used to study the water quantity requirements and regional hydrologic impacts such as the areal extent of the drawdown cone and the recovery time for water levels in an aquifer after mining operation have ceased for open pit mine dewatering under numerous cases for various aquifer systems.