Solution of 2D nonstationary problem of hydrogeology for groundwater level detection in different phases of open pit mining

Abstract

Solution of any problem of hydrogeology, especially pit wall slope stability design, needs information on groundwater levels in different phases of open pit mining. The groundwater level is mostly determined from the numerical modeling of fluid flows. The unsteady fluid flow modeling is a labor-consuming process and it often involves 3D methods of finite elements, finite volumes and finite differences, which requires much time and is sometimes impossible because of the lack of the source data. The fastest way of determining groundwater levels and fluid flow parameters in wanted directions at different times of open pit mining is the solution of 2D nonstationary problem of hydrogeology using the finite element method. The problem solving details are insufficiently described in technical literature, and the present authors instantiate the process by comparing the Rocscience Slide 2 application with the analytical solutions. The 2D unstable groundwater flow in the pit wall was modeled for 5 time periods: open pit mine life for 1460 days; every year until termination of open pit mining; time of the steady-state flow setting 25 years long. The modeling domain is found based on the open pit mine geometry, topography and impact radius. The impact radius is 1357 m. The model identifies a single aquifer with the permeability of 0.69 m/day. The model groundwater level deviates from the in-situ measurements taken in observation wells at a distance of 23 m by 2.5 %.