Groundwater Flow Modeling and Slope Stability Analysis for Deepening of Mae Moh Open Pit Lignite Mine

Abstract

This study deals with modeling the groundwater pressure effect and slope stability analysis of C1 pit on deep pit mining of Mae Moh open pit lignite mine, Thailand. Groundwater flow model was constructed and run using Visual Modflow 3D. The groundwater model consists of two aquifers and one aquitard, which were then divided into nine material types for property designation. The predictive simulations were carried out for seven years (2010 to 2017) according to the mine development plan. Results showed that low permeable Argillite underlying the west wall of C1 pit is problematic as low drawdowns were obtained for short term pumping from Argillite formation. Long term pumping schedules must be initiated to lower the potentiometric head within Argillite formation by pumping from limestone under Northeast (NE) pit. Stability of the west wall of the C1 pit for 2017 pit slope was evaluated in terms of the safety factor by the limit equilibrium method. Results obtained in this study indicated that the west wall is susceptible to failure due to water pressure associated with it. To maintain a safe slope, potentiometric head within west wall of C1 pit should be maintained below 170m, MSL.