Breakage and Permeability Reduction of Tailings Sand under High-Pressure Oedometric Compression and Creep

Tailings dams are constructed as a means of containing the byproducts of mining operations. They are often built using the coarser fraction of the tailings referred to as the tailings underflow or tailings sand. Due to the expected high overburden pressure, grain crushing may occur at the base of tall tailings dams. This may result in reduced hydraulic conductivity or drainage capability, thus undermining the long-term performance of the dam. To accurately evaluate the safety margin when designing tall tailings dams, it is important to understand the evolution of the hydromechanical behavior of the tailings sand. In this paper, laboratory-scale high-stress compression tests were conducted, and hydraulic conductivity measurements were taken using a specially designed oedometer cell. The experimental results were then analyzed using an enhanced continuum breakage mechanics model. The results indicate that an increase in stress from 5 to 40 MPa can result in an increase in fines content (mass percentage of particles smaller than 0.075 mm) from 11% to 17% and a corresponding decrease in hydraulic conductivity of up to one order of magnitude for the tested materials. We also report the preliminary results of a three-month creep test on tailings sand subjected to 3 MPa confining pressure to study the time effect associated with grain crushing.