Effects of layering on the mechanical properties of cemented tailings backfill under unconfined compression

Abstract

This study investigated the mechanical behaviour of layered cemented tailings backfill. Indeed, paste backfill in low stopes can be poured completely at once. However, this strategy is difficult in large stopes since it exerts excessive pressure on the barricade leading to the failure of the barricade. As result, layer-by-layer backfilling poured within a 24-hour interval is adopted. This practice leads to the stratification of the backfill structure which then results in a layered backfill body. Several studies on backfill bodies have neglected the effect of layering on the mechanical strength of the backfill structures. This study attempted to close this gap by incorporating the shear force between the layers in the estimation of the safety factor of the backfill structure. In order to study the mechanical behaviour of layered cemented backfill, laboratory tests, numerical simulations and mathematical modelling were conducted. Uniaxial compressive strength tests were performed using an unconfined compression machine. The OPTUM G3 software package, on the other hand, was utilised for numerical analysis. The limit equilibrium wedge solution was used to evaluate the stability of layered cemented backfill while results from the laboratory tests were used to develop a deformation model of layered cemented backfill. It was concluded from the deformation model that the strength of cemented backfill decreases with increasing layers of backfill at early age (14 days). Nonetheless, the strength of layered cemented backfill gradually increases when more layers are added. The limit equilibrium solution was also improved by incorporating the shear forces acting along the backfill-backfill interfaces and the sliding plane. The limit equilibrium solution also demonstrated a decreasing safety factor when the shear force along the backfill interfaces is included. In contrast, the safety factor decreased with increasing stope height. It is however recommended in future that advanced numerical analysis is explored to develop stability graphs that would predict the waiting period for the backfill body to set till the next blast. This would pave the way for improved safety and productivity of mines.