【正文】 f having permeabilityvalues much less than the 100 mm threshold suggestedby Herget and De Korompay [3], each of these hydraulicHorizontalaccess drivePorous barricadebrick wallHorizontalaccess driveDecant waterHydraulic fillSlurry entersstope1169Production 14 (2020) 1168e1175Fig. 2. An idealised stope with two sublevel drains.fills has performed satisfactorily. Anecdotal evidencesand back calculations using the measured flow inthe mine stopes suggest that the permeability of thehydraulic fill in the mine is often larger than what ismeasured in the laboratory under controlled conditions.Kuganathan [5] and Brady and Brown [6] proposedpermeability values in the range of 30e50 mm/h, whichare significantly larger than those measured in thelaboratory for similar fills. These values are much lessthan the threshold limit prescribed by Herget and DeKorompay [3], suggesting that it is a conservativeremendation.. Stability considerationsThe stability of the hydraulic fill stope during andafter the drainage period depends on several parametersthat determine the strength and the sti?ness of thehydraulic fill mass. These parameters can be measured inthe laboratory using reconstituted samples or in themine using in situ testing devices. Due to the di?cultiesand high costs associated with carrying the in situ testingrigs into the underground openings, laboratory tests arethe preferred alternatives.Strengthandsti?nessaredirectlyrelatedtotherelativedensity of the fill. When the hydraulic fill is denser, therelativedensityandfrictionanglearehigher,andthusthefill is more stable. In geotechnical engineering, there areseveral empirical correlations relating relative density totheYoung’smodulusandfrictionangleofagranularsoil.. Maximum and minimum dry density testsA larger void ratio does not always mean a loosergranular soil. Relative density is a good measure ofthe density of the grain packing, and depends on themaximum and minimum possible void ratios for the soilwhilst still maintaining intergranular contact. Theminimum void ratio is generally determined by pouringthe dry tailings from a fixed height so that the grains areplacedataveryloosestate[7].Themaximumvoidratioisgenerallyachievedbysaturatingthetailingsandvibratingthem to attain dense packing [8]. These two extreme voidratios provide the lower and upper bound for the voidratios, and, depending on where the current void ratioof the hydraulic fill is, the relative density is defined as:DrZemaxC255ecurrentemaxC255emin!100% 240。 Geotechnical1. IntroductionIn the mining industry, when underground ore bodiesare extracted, verylarge voids are created,which must beuse of the waste rock or tailings that are consideredbyproducts of the mining operation. This is an e?ectivemeans of tailing disposal because it negates the needfor constructing large tailing dams at the surface. Thebackfilling ofunderground voids also improveslocal andregional stability, enabling safer and more e?cientis a major issue in Australia, where 10 million cubicmetres of underground voids are generated annually asa result of mining [1].There are two basic types of backfilling strategies.The first, uncemented backfilling, does not make use ofcan be studied using soil mechanics theories. A typicalexample of uncemented backfilling is the use ofhydraulic fills that are placed in the form of slurry intothe underground voids. The second category, cementedbackfilling, makes use of a small percentage of bindersuch as Portland cement or a blend of Portland cementwith another pozzolan such as fly ash, gypsum or blastfurnace slag.The purpose of this paper is to analyse the findingsfrom an extensive laboratory test programme carriedout in Australia on hydraulic fills and several barricadebricks. Hydraulic fills are uncemented techniques, andare one of the most widely used backfilling strategies inAustralia. More than 20 di?erent hydraulic fills,representing a wide range of mines in Australia, werestudied at James Cook University (JCU). The grain sizedistributions for all of these fills lie within a narrowGeotechnical considerations inN. Sivakugana,*, . RankineaSchool of Engineering, James CookbCannington Mine, BHP Billiton, .Received 1 March 2020。b,Universit1C211 2020 Elsevier Ltd. All rights reserved.Keywords: Hydraulic fills。 Paste fills。m)Percent finer by weight Australian hydraulic fillsCemented hydraulic fillPaste fillFig. 1. Typical grain size distribution curves for hydraulic fills,cemented hydraulic fills and paste fills.N. Sivakugan et al. / Journal of Cleanerlocated at upper levels act as exit points for the decantedwater, and also serve as drains when the hydraulic fillrises in the stope.. Drainage considerationsDrainage is the most important issue that must beconsidered when designing hydraulic fill stopes. Therehave been several accidents (namely, trapped miners andmachinery) worldwide caused by wet hydraulic fillrushing through horizontal access drives (Fig. 2).Several reasons, including poor quality barricade bricks,liquefaction, and piping within the hydraulic fill areattributed to such failures [2]. Therefore, permeability ofthe hydraulic fill in the stope is a critical parameter inthe design。2222。1C2552y222。3222。2020. p. 161e5.[7] ASTM D 4254e91. Standard test method for minimum indexdensity and unit weight of soils and calculation of relative density.Annual book of ASTM standards. .: American Society ofTesting Materials。 1998. p. 111e6.[3] Herget G, De Korompay V. In situ drainage properties ofhydraulic backfills. Research and innovations, CIM specialvolume。97(SM9):1207e25.[10] Clark IH. The properties of hydraulically placed backfill. In:Proceedings of backfill in South African mines. Johannesburg:SAI