【正文】 photograph of (a), a barricade brick and (b), an underground,the walls have been constructed in a vertical plane,but the recent industry trend has been to increase wallstrength by constructing them in a curved manner, withthe convex toward the hydraulic fill as shown in Fig. 6b.Although it is known within the mining industrythat the porous bricks used in underground barricadeconstruction are prone to variability in strength properties [5], the manufacturers often guarantee a minimumFig. 6. Porous brick barricade. (a) A brick, (b) brick barricade under1172 N. Sivakugan et al. / Journal of Cleanerconstruction in a mine.value for uniaxial pressive strength for the bricks inthe order of 10 MPa [11]. Kuganathan [5] and Du?eldet al. [11] have reported uniaxial pressive strengthvalues from 5 MPa to over 26 MPa.A series of uniaxial pressive strength testsundertaken on a large sample of brick cores havedemonstrated the scatter of results, but more importantly, have highlighted a distinct variation in brickperformance when saturated, as it would occur in themines. Two identical cylindrical cores were cut from 29porous barricade bricks. One of the brick cores fromeach of the individual bricks was tested dry, and theother core was tested after having been saturatedfor either 7 or 90 days. The strength and deformationparameters (namely, the uniaxial strength, Young’smodulus, and the axial failure strain) for the wet anddry cores are shown in Figs. 7e9.Firstly, the extreme scatter between all results reitertheaverageuniaxialpressivestrengthofdrybrickstofallbetween6and10 MPa,whenthebrickmanufacturersguarantee minimum of 10 MPa. It can also be seen fromthis figure that there is a distinct loss of pressivestrength as a result of wetting the brick. There was nosignificant di?erence between 7 and 90 days soaking,implying that the strength loss occurs immediatelyupon wetting. This loss appears to be in the order ofapproximately 25%, which is notable considering thatbricksaregenerallyexposedtosaturatedconditionswhenplaced underground, and all manufacturer strengthspecifications are based on bricks that are tested dry.The sti?ness also appears to be reduced by wetting(Fig. 8). The Young’s modulus of the dry cores rangedbetween 1 and MPa. The length of time the brickswere wetted did not have a significant impact onthe magnitude of the reduction in sti?ness. The peakfailure axial strain was not reduced by wetting (Fig. 9).The cores in general failed under an axial strain of lessthan 1%.The porous bricks are designed to be free drainingand therefore, their permeability is at least an order ofmagnitude greater than that of hydraulic fill. The02468101214086421012Uniaxial pressive strength of dry core (MPa)Uniaxial pressive strengthof wet core (MPa)90 days7 days14Production 14 (2020) 1168e1175Fig. 7. Uniaxial strength of dry and wet bricks.barricade bricks have proven, over time, to satisfy thefreedraining situation, and the reduction of permeability through mitigation of fines has not been recorded.Rankine et al. [4] carried out constant head and fallinghead permeability tests on several barricade bricks andreported permeability values in the order of 3500 mm/h,three orders of magnitude greater than the permeabilityof the tailings.4. Paste fillLike hydraulic fill, paste fill falls into the category ofthickened tailings. A conceptual framework to describethickened tailings in terms of concentration and strengthis shown in Fig. 10 [12,13]. Paste fill is prised of fullmill tailings with a typical e?ective grain size of 5 mm,mixed with a small percentage of binder, in the order of3e6% by weight, and water. It is the densest form ofbackfill in the spectrum of thickened tailings placedunderground as a backfill material. The acceptance ofpaste backfill as a viable alternative to hydraulic slurryand rock fill did not truly occur until the mid to late1990s with the construction and successful operation ofseveral paste backfill systems in Canada and the BHPBilliton Cannington Mine in Australia.010 1 7 days90 days012340 1 2 3 4Young39。68:47e53.[13] Jewell RJ. Introduction. In: Jewell RJ, Fourie AB, Lord ER,editors. Paste and thickened tailings: a guide. Perth (Australia):U。D 240。 Backfills。1Cy222。 2020.p. 218e24.[5] Kuganathan K. Mine backfilling, backfill drainage and bulkheadconstruction e a safety first approach. Australia’s miningmonthly February, 2020。1175N. Sivakugan et al. / Journal of Cleaner Production 14 (2020) 1168e1175barricade walls.Paste fill contains at least 15% of grains finer than20 mm, and the e?ective grain size (D10) is in the order of5 mm. The 3e6% binder improves the strength and thusstability significantly. The large fine content within thepaste fill enables most of the water to be held to thesurface of the grains, and therefore drainage is not aconcern in paste backfilling.AcknowledgementsSeveral mines have contributed cash and inkindto the research discussed in this paper. Their supportis gratefully acknowledged. Senior Technical O?cersMr. Warren O’Donnell and Mr. Stuart Petersen assistedin most of the laboratory test work carried out on thebricks and hydraulic fills. Our regular discussions withMr. Richard Cowling of Cowling Associates were veryvaluable throughout our mining research.References[1] Grice T. Recent mine developments in Australia. In: Proceedingsof the 7th international symposium on mining with backfill(MINEFILL)。1222。 accepted 3 June 202026 April 2020of a mine operation. In the Australian mining industry, wherebackfills deployed. Many accidents reported at hydraulic fillof their behaviour and barricade bricks. This papercarried out in Australia on more than 20 di?erent hy