Coupled two-dimensional finite element modelling of mine backfilling with cemented tailings

Abstract

Mine backfilling is a process whereby mine tailings mixed with small amounts of cement are placed hydraulically into mined-out voids (“stopes”) to stabilize the rockmass and allow full extraction of adjacent ore. A containment barricade is constructed to block the access point at the base of the stope, the design of which requires calculation of the total stress on the barricade during and following filling. For fine-grained backfill containing cement, the rate of development of stresses is governed by the rates of filling, consolidation, and cement hydration, each with its own timescale. As “consolidation” in backfill undergoing hydration can be dominated by “self-desiccation”, this mechanism must also be incorporated. Interaction between the backfill and the stope walls (“arching”) also has an influence. The paper describes a finite element (FE) model (“Minefill-2D”) that can model these interactions, although only in a two-dimensional (plane–strain or axisymmetric) fashion. It is shown that arching significantly influences the total stress distribution in a typical stope during filling, but only if and when effective stress develops. For cemented backfill, arching sometimes does not fully mobilize the cement bond strength, so that assessment of arching using traditional limit equilibrium methods is often not appropriate.