Rheological properties and flow behavior of mine tailings and fly ash: Lessons from failures

Embankment dam failures at mine tailings and coal ash impoundments often trigger fast-moving slurry flows that can travel miles, causing severe environmental and structural damage. To predict such flows in future failures, numerous studies have focused on understanding slurry flow behavior, particularly through yield stress measurements. Yield stress is typically assessed using either rheological tests or slump/flow tests. However, significant uncertainties remain regarding which method more reliably measures the yield stress of tailings and fly ash slurries. This study presents results on six fly ash and six granular materials such as mine tailings. Yield stress obtained from rheometer tests were compared to those derived from flow tests. Results show that yield stresses calculated from flow tests were consistently higher than those measured using rheological methods for all fly ash and silica-based materials. Notably, fly ash slurries exhibited higher yield stress than granular soil slurries.