Cemented paste backfill (CPB) has been utilised globally in mines based on its benefits of non-segregation, non-bleeding and homogeneity. Due to a lack of research around the mechanism(s) driving anti-segregation properties, nowadays only some engineering empirical parameters including the slump or the fine particle content of backfill slurries can be used as the descriptive criterion for CPB. To better understand the antisegregation mechanism of CPB, so a quantitative criterion for its identification can be determined, the segregation-induced inhomogeneous properties of cemented tailings backfill have been experimentally investigated. Samples (diameter 75 mm and height 150 mm) with different solid contents were poured, cured and cut into sections of equal height. Thereafter, titration measures of EDTA-2Na and helium porosimeter have been used respectively to test the cement content and porosity of each section. Results show that the cement contents decreased from top to bottom along the curing height of samples, while the porosities increased along the settling direction. The inhomogeneity of cemented samples is affected obviously by the solids content of the paste, and it is notable that there is a turning point for the slurry concentration value over which the homogeneity will be improved dramatically. The turning point could be used as a new criterion for CPB definition from the perspective of inhomogeneity inhibition.
Cemented paste backfill (CPB) has become known as a superior secondary ground support technique and mine tailings storage method for stoping. Extensive scientific research has been conducted by the authors on CPB to provide the Red Lake operation (RLO) of Evolution Mining with an optimised backfill placement process. Due to these complex factors and interactions, a rational CPB material design process was assessed to demonstrate the safety aspects related to a continuous pour. For this purpose, an extensive field monitoring program was required to quantify the CPB performance and characteristics. There are two different ways of optimising the CPB design to maximise placement rate: (i) optimising the type and amount of binder added to the system, and (ii) optimising the CPB placement process underground. Optimisation of binder type and dosage is relatively easy as the required backfill stand-up strength is based on block dimensions, stope stability, and extraction sequencing. Four stopes were instrumented with total earth pressure cells (TEPCs) and piezometers to capture the pressures acting on the fill fence structures and the strengthening response of the CPB plug within the stopes. This paper summarises the results of each of the tests performed. Based on the results obtained from this study, it was concluded that RLO can safely conduct continuous CPB pours with appropriate safeguards and protocols in place. It is important to note that this paper is a summary of the CPB performance and characteristics in RLO longhole stopes and does not reflect site-specific safety procedures, protocols, and critical controls required for a more aggressive pouring regime.
In this study, the strain localisation behaviour of a South Australian coppergold 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 stressstrain relations of CPB samples than conventional external measurement devices. The DIC test results indicate that strain localisation of CPB samples initiates in the prepeak 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 prepeak regime and more pronounced in the post-peak regime.
Until mid-2020, the Newmont Éléonore mine cemented paste backfill (CPB) recipes were chosen from charts comparing binder contents and strengths at specific curing ages up to 56 days. However, these charts were based on Mitchells method using Éléonores biggest stope dimensions. They also did not consider any rheology, maximum surface pump pressure capacities or mix density. Using the new system, and its resulting template, backfill personnel can tailor a recipe for each stope to meet the latest sequence and environment conditions. This paper explains how the new paste recipes are selected, as well as the costs savings and productivity increases they enabled.