【正文】 the early research performed on paste fillswas on the transportation and deposition of the paste,the majority of the definitions of the paste are based onits rheological characteristics. Table 1 summarises somemon characteristics of the thickened tailings continuum shown in Fig. 10 [14]. Hydraulic fills fall into thethickened tailings profile. A significant di?erence to noteis that the water content in paste fill is retained onplacement, through the large surface area of the grains,eliminating the need for the design of drainage of the fillor barricades.Thedesignrequirementsforpastefilledstopesarethenreduced to static and dynamic stability requirements. Bydesigning the fill masses with su?cient strength to ensurethe vertical faces of the back filled stopes remain stablethroughout the mining of the adjacent stopes, the staticstability requirements are satisfied. If the paste beesunstable, the adjacent faces may relax and displace intothe open stope, causing high levels of dilution and loss ofmining economies. The required strength of the backfillsis typically calculated using analytical solution techniques [15e17]. More recently, numerical modellingsolutions [18,19] have been used to determine backfillstability throughout the entire mining sequence.The dynamic stability of the paste fill stopes isaddressed by designing the backfill mass to resist liquefaction or other seismic activities. Due to the increasedresidual moisture content of paste, there is an increasedliquefaction potential risk for the paste. Clough et al.[20] showed that cemented sand with a uniaxial 0 1A Measure of ConcentrationA Measure of Strength1SLURRY(segregates)PASTE(nonsegregating)CAKE(nonpumpable)Fig. 10. Thickened tailings continuum [13].1173Production 14 (2020) 1168e1175pressive strength of 100 kPa was capable of resisting78minimumfills, due to the absence of drainage capabilities. Thebarricades are designed as temporary structures in pastefill stopes. The walls must be designed to retain theliquid mass of the fill, until such time as it has curedsu?ciently to act as a plug at the base of the stope, thuspreventing the additional deposited paste from enteringthe mine workings.5. Numerical modellingIn largescale underground mining operations, wherein situ monitoring of stresses, strains, displacements andpore pressures is often very di?cult, expensive or notfeasible at all, the use of numerical modelling techniquesbees extremely valuable in understanding and predicting the behaviours of both the materials and thesystems being modelled.FLAC and FLAC3Dare explicit, finite di?erencesoftware packages specifically designed for solving geotechnical and mining problems in two and three dimensions, respectively. The research group at JCU has used3D6. ConclusionsCemented backfilling and uncemented backfilling arethe two strategies used in mine backfilling in Australia.Hydraulic fills and paste fills are examples of uncemented and cemented backfills, respectively. A series oflaboratory tests carried out at James Cook Universityon more than 20 di?erent hydraulic fill samples suggestthe following:C15 The hydraulic fill, placed in the form of slurry, settlesto relative densities of 40e70%, paring well withthe field measurements.C15 Specific gravity of the hydraulic fill grains rangefrom to .C15 All of the reconstituted hydraulic fill samplessedimented in the laboratory, simulating the slurryplacement in the mine, settled to a void ratio of ,and porosity of 40%.C15 From constant head and falling head permeabilitytests carried out on the hydraulic fill samples, thepermeability was measured to be in the range ofa seismic activity measuring on the Richter scale.This figure has been adopted by the mining industry asthe minimum design strength fill for any fill mass. Thestrength of the paste satisfying the static stabilityrequirements are generally in excess of dynamic strengthrequirements.Barricades are designed as underground retainingwalls. The structural design and construction of thewalls may vary slightly to those designed for hydraulicTable 1Material properties for thickened tailings continuum [14]Material property Slurry ThickenedParticle size Coarse fraction only. No particlesless than 20 mm. Segregationduring transportation and orplacement is dependent only onthe coarse fractionSomefinesfrommoresegregateduringdependentPulp density (%) 60e72 70eFlow regimes/linevelocitiesCritical flow velocity. To maintainflow must have turbulent flow(velO2 m/s). If vel!2 m/ssettling occursCriticalmustIf velNewtonian flow NewtonianYield stress No minimum yield stress NoPreparation Cyclone CycloneSegregation in stope Yes/high Slight/partialDrainage from Stope Yes Partial/limitedFinal density Low Medium/hiSupernatant water High SomePost placement shrinkage High InsignificanRehabilitation Delayed ImmediatePermeability Medium/low Low1174 N. Sivakugan et al. / Journal of CleanerFLAC insimulatingthefillingoperationsinahydraulicfill and paste fill stopes, studying the developments ofstresses and drainage within the fill [19,21].The intention of this paper has not been to detail thefindings from these simulations but rather to highlightthe potential these modelling tools have to dramaticallyincrease the confidence with which stope predictionsmay be made, ultimately leading to optimised mineoperation and safety.tailings Pastefines included (typically !15%),content tends to modify behaviourslurry e . rheological characteristicssimilar to paste, however doeswhen bought to rest. Segregationtransportation and or placement isonly on the coarse fractionAdditional/most fines(typically 15% (min)O20 mm78e82flow velocity. To mainta