Behavior of Cemented Paste Backfill in Two Mine Stopes: Measurements and Modeling

Over the past decade there has been increasing use of “paste” for backfilling of mined-out voids (“stopes”) in underground mines. Paste backfill is generated from full stream tailings and is almost always placed underground with cement. This paper presents field measurements and back analysis of two different cemented paste backfill (CPB) cases. Using the collected data and subsequent back analysis, the writers show that these two cases demonstrate considerably different consolidation behaviors, which in turn influence critical design and management aspects such as applied barricade stresses and choice of an appropriate curing technique for laboratory control specimens. The paper presents pore pressure and total stress monitoring data gathered from two different CPBs during the deposition process. Both filling cases are modeled using Minefill-2D, which is a finite-element (FE) model capable of fully coupling the time-dependent processes of fill accretion, consolidation, cement hydration, and stress arching. Input parameters for the model are obtained from independent laboratory tests. Comparison between measured values and those calculated based on laboratory measurements verifies that, in general, the model provides a good representation of the process. However, there are some significant difficulties relating to modeling a three-dimensional stope with a two-dimensional plane-strain FE program, and some ways of accounting for these difficulties are explored. The model is then used to extrapolate the measured results to investigate the influence of varying filling rate, cement content, and number of drawpoints on critical design aspects.