Determination of mine-wide in-situ stress using numerical back analysis: a case study of Jwaneng mine

In order to prepare for the transition from open pit to underground mining, Jwaneng Mine has undertaken several in-situ stress measurement campaigns in the past 12 years. Complex geological conditions at the mine site result in significantly scattered measurement data, making it challenging to interpret a coherent trend for the field stress tensor. To address this issue, this study presents a method to determine the mine-wide in-situ stress field using numerical back analysis incorporating geology, field stress measurement data, and mining history. Firstly, to consider the impact of excavation effects and the complex geology of the mining area, a 3DEC numerical model is established that includes major faults and rock mass zones and considers the open-pit excavation history. Thereafter, a back-analysis approach using the least squares method is proposed to find the optimal solution of the stress field. Based on this, the solution of the field stress tensor at Jwaneng Mine is obtained using overcoring stress measurement data obtained from 2013 to 2019. The reliability of the solution is further validated using the measurement data of deformation rate analysis and borehole ovality. This study offers reliable mine-scale in-situ stress conditions for Jwaneng Mine, which is critical for underground mine design. The proposed back-analysis method is useful for estimating mine-wide field stress under complex geological conditions.