A 3D groundwater flow model was constructed using MINEDW [1]to simulate pore pressure at the Chuquicamata open pit mine slope in Chile. Three main factors required the implementation of a 3D model for the prediction of pore pressures: (1) discrete zones of recharge in the gravel zone lead to the non-uniform flow field; (2) the low-permeability west fault and shear zones maintain the non-hydrostatic pore-pressure distribution with depth during mining; and (3) the drainage gallery causes localized depressurization. In addition, a zone of relaxation (ZOR) was observed at the site. Simulations of the development of the ZOR according to the mining schedule are important in the prediction of pore-pressure distribution within the slope. The model was calibrated against measured water levels, pore pressures, drains, and seepage rates. The calibrated model was then used to simulate and predict pore-pressure distribution in the pit walls for different time periods. Specifically, the model was able to capture the non-hydrostatic, transient nature of the pore pressures with depth in the granodiorite west of the shear zone, in the shear zone, and along the west fault. The model also simulated the ZOR for the first 150 m below the pit bench with enhanced hydraulic conductivity values according to the excavation schedule. Simulated transient 3D pore-pressure distribution provides a more realistic input to 3DEC slope-stability analyses.
Chuquicamata is a large open pit mine located 15 km north of the city of Calama in the Atacama Desert, Chile. It is 250 km northeast of Antofagasta, and 1,200 km north of Santiago. A three-dimensional groundwater flow model (3D flow model) was constructed to simulate the groundwater conditions at the mine. The primary purpose of the flow model was to predict pore-pressure distribution as input to the on-going geomechanical model.
