Strain localisation behaviour of cemented paste backfill

Abstract

Mine tailings are the most significant and most problematic sources of solid waste globally in the mining industry. The developing concept of sustainable mining warrants reusing mine wastes, particularly tailings. Cemented paste backfill (CPB) is a backfill method composed of dewatered tailings, a cementitious binder, and processed mine water. CPB reuses tailings in underground mine excavations, and as such, reduces the amount of surface-disposed tailings, mitigates the potential environmental impacts, and assists waste management. In this study, the strain localisation behaviour of a South Australian copper–gold underground mine CPB system was evaluated through a comprehensive experimental programme. Understanding the strain localisation behaviour helps evaluate CPB damage evolution and failure mechanism under real-life loading regimes. The three-dimensional digital image correlation (DIC) technique was used to measure the full-field of strain development on the surface of CPB samples during unconfined compressive strength (UCS) tests. With the use of several virtual extensometers, the axial and lateral strains of CPB samples, with and without strain localisation, in both pre-peak and post-peak regimes are characterised. Overall, the DIC technique provides more accurate stress–strain relations of CPB samples than conventional external measurement devices. The DIC test results indicate that strain localisation of CPB samples initiates in the pre-peak regime at around 80% of the UCS. The greater the binder content and the longer the curing time, the higher the axial stress level required to initiate localisation to the UCS, thus emulating the failure mechanism of quasi-brittle materials – rock and concrete. Finally, with the increase of curing time, the difference between strain values at the localised and non-localised zones became less significant in the pre-peak regime and more pronounced in the post-peak regime.