Optimization of Pillar Design for Potash Deposits of Khorat Basin, Northeast Thailand

Khorat Basin is the biggest evaporite basin of Thailand where there is a huge potash deposit underneath this basin. Potash in Khorat Basin is located in Maha Sarakham formation overlying the lower rock salt which have the depth of more than hundred meters. Underground mining method called ‘Room and Pillar’ is one of the most suitable methods to extract potash. However, there is no intensive study on pillar design for potash of Thailand yet. This work offers a procedure to determine the optimal dimension of pillar for underground potash mine in Thailand, especially under Khorat, which in turn provides the best balance between extraction ratio and stability. The design is focused on both regular pillar and barrier pillar. The study has been carried out using both empirical and numerical analysis. Obert and Duvall relation equation, for estimation the pillar strength in an underground coal mine, is adapted in empirical case studies which is then calibrated with numerical modeling by using FLAC3D. Mechanical properties of potash from Khorat Basin are chosen as the input parameters of the study. The result of optimal dimension of pillar is represented by safety envelop which is constructed utilizing simulated result from numerical analysis. The safety envelops illustrate the decrease of 10% in extraction ratio when the depth is increased from 200m to 300m. As expected, the empirical equation is not suitable for estimating strength of potash in Thailand yet. The study of slenderness constants is the key for modifying the equation above to be applicable for potash in Thailand. The result finally shows the capability of modified formulas for effectively estimated pillar strength.