Soft-rock mines encounter several ground control challenges. Roof and rib instability, manifesting as rock falls, spalling (skin failure), or larger blocky failures, is common, influenced by weak rock strata, geological discontinuities like faults or cleats, and mining-induced stresses.
Soft rock miners excavate softer minerals like salt or coal. There are many technical services jobs required underground to support the miners (Government of Canada, 2024).
Pillar failure, including catastrophic cascading collapses, can occur when pillars are undersized, extraction ratios are high, or width-to-height ratios are low, leading to load transfer and progressive failure (NIOSH, 1997b).
Floor heave, or “squeeze,” is another significant issue, particularly where clay-rich or weak floor materials exist. This upward buckling of the mine floor happens when the load exceeds the floor’s bearing capacity, potentially obstructing passages (University of Kentucky Geological Survey, n.d.).
Squeezing ground conditions, characterized by large-scale deformation, are prevalent in weak rock masses under high stress, often exacerbated by geological structures like foliation (Mercier-Langevin & Hadjigeorgiou, 2010).
In evaporite mines (e.g., potash, salt, trona), time-dependent deformation or creep is a concern, as it can gradually shift stresses to stronger, brittle overlying strata, potentially causing sudden, violent failures (Maleki & MSHA, n.d.). Water ingress in such mines also poses a serious threat by eroding pillars and compromising overall stability (Evans et al., 2017).
Recognizing signs like fresh cracks, damaged supports, or unusual rock noises is crucial for early detection of these ground problems (Canadian Centre for Occupational Health and Safety, 2024).
What are some warning signs miners should look for to detect ground instability early?
References:
Canadian Centre for Occupational Health and Safety. (2024). Underground Mining – Health and Safety. https://www.ccohs.ca/oshanswers/occup_workplace/underground_mining.html
Maleki, H., & MSHA. (n.d.). Catastrophic failure of three large evaporite mines – Case studies and lessons learned. https://stacks.cdc.gov/view/cdc/161161/cdc_161161_DS1.pdf
Mercier-Langevin, P., & Hadjigeorgiou, J. (2010). Squeezing ground in hard rock mines – Observations from three Canadian underground operations. In Deep Mining 2010: Proceedings of the Fifth International Seminar on Deep and High Stress Mining. Australian Centre for Geomechanics. https://papers.acg.uwa.edu.au/d/1074_10_Mercier-Langevin/10_Mercier-Langevin.pdf
NIOSH. (1997b). Catastrophic Pillar Failures: A Potential Hazard in Room-and-Pillar Mines (Report of Investigations 9642).https://stacks.cdc.gov/view/cdc/9341/cdc_9341_DS1.pdf
University of Kentucky Geological Survey. (n.d.). Coal Mining Geology: Floor Heave. https://www.uky.edu/KGS/coal/coal-mining-geology-floor-heave.php
