In-Situ Stress Measurements for Stability Analysis of Room and Pillar Rock Salt Mines: A Case Study from the Salt Range, Punjab, Pakistan

ABSTRACT: Room-and-pillar mining is a widely used method for rock salt extraction in underground mines, where pillar stability plays a critical role in ensuring mine safety and optimizing mineral recovery. This study investigates in-situ stress conditions in three underground rock salt mines in Pakistan using the flat jack method. Field measurements included pillar stresses, in-situ elastic modulus, and key geometric variables such as pillar dimensions, opening width-to-height ratio, extraction ratio, and overburden height. Additionally, salt block samples were collected for laboratory testing to determine geomechanical properties, including uniaxial compressive strength, Young's modulus, Brazilian tensile strength, and density. The results indicate that pillar stresses are proportional to overburden stress, with values ranging from 6.05 MPa to 11.97 MPa, confirming overall pillar stability. Regression analysis was performed to develop predictive models for in-situ stress and elastic modulus. Furthermore, a guideline chart was developed to assist in determining appropriate pillar dimensions for various spans and safety levels, providing a practical tool for mine design and stability assessment.