Cement-Enhancing Mechanical Behavior of Tailings Behind Upstream Tailings Dam for Safe Decommissioning

Catastrophic failures of tailings dams, primarily due to liquefaction, have occurred in Brazil in the last few years. Mine tailings deposited behind upstream dams are materials of low in situ densities and strengths. To avoid future disasters, chemical improvement methodologies such as deep mixing and mass stabilization technologies are being studied as alternatives to be used before decommissioning for in situ improvements of upstream tailings dams with a high risk of collapse. The present research aims to analyze the mechanical behavior of reconstituted state gold tailings specimens, in contrast to artificially cemented gold mine tailings specimens, considering the use of small and large amounts of Portland cement under a similar high void ratio. The influence of Portland cement content in the stabilization of gold tailings specimens molded with their in-situ void ratio was evaluated through saturated undrained triaxial compression tests carried out under small confining pressures. A reduced amount of Portland cement (about 12 kg/m3) was enough to avoid liquefaction (with the generation of negative pore-pressure), keeping the same unique critical state line (CSL) for reconstituted tailings and slightly cemented tailings specimens, with a gradient (Mtc) of 1.41. The use of high amounts of Portland cement insertion (75 and 150 kg/m3) caused an alteration in the ultimate condition of the studied tailings, and Mtc changed to 2.36. Finally, the in-situ addition of Portland cement to tailings deposited behind upstream dams is an important alternative for the safe decommissioning of such structures.