STRESS ISSUES IMPACTING DESIGN AND STABILITY AT OCI WYOMING'S BIG ISLAND TRONA MINE

摘要

Room-and-pillar mining at the Big Island Mine uses narrow,yield (i.e., load transferring) pillars to achieve high resource recoveryand productivity. Two flat-lying 3- to 3fi-meter (10- to 11fi-ft) seamsare mined. The interburden between the seams is about 10 meters(33 ft) and the cover depth is 250 to 330 meters (820 to 1,080 ft).Most of the mining has been single-seam, but two-seam mining willbegin in the near future. Yield pillars minimize stress transfer betweenthe seams. However, it is important that good long-term stability bemaintained to prevent subsidence over a large portion of the minebeneath the Green River channel.Three stress issues impacting stability are discussed in thispaper: (1) higher-than-gravity vertical pre-mining stresses, (2) timedependentstress transfer or arching, and (3) stresses induced bystrata gas. Although the stress environment and behavior is not fullyunderstood, steps have been taken in mine design and operations tominimize impacts to stability. Stress determinations have been veryimportant to verify analytical predictions used in mine design and inlong-term stability assessment.