August 2007 1 Paper 20 Minefill INTRODUCTION In a recent survey of Canadian underground backfill practice, De Souza, Archibald, and Dirige (2003) report that over 55% of backfill system fail- ures relate to the distribution system. As shown in Figure 1, these failures are due to: • plugs (blockages) in pipelines and boreholes (35% of total failures and 63% of distribution system failures); • pipeline bursts (12% and 22%, respectively); and • pipe hammering (8.5% and 15%, respectively). Considering the maturity of backfill system technology, this high incidence of failures attrib- uted to distribution systems should be considered unacceptable. Some of the blockage incidents are likely to be related to the supply of out-of-specification backfill to the distribution system. This issue can be tackled by implementing more stringent quality control measures at the backfill plant. Backfill pipeline distribution systems— design methodology review R. Cooke, Paterson & Cooke, Denver, Colorado, USA ABSTRACT Despite the technology for designing backfill distribution systems being mature, a recent survey of Canadian backfill operations reveals that the majority of underground backfill system fail- ures relate to the distribution system (blockages, pipeline bursts, and hammering). While some of the failures may be related backfill quality control, the majority of the problems are likely related to the design of the backfill distribution system. This paper presents a review of the design process for backfill distribution systems, highlighting the differences between hydraulic and paste fill systems. KEYWORDS Backfill, Paste, Slurry, Distribution The causes of the remaining distribution system- related failures may in many cases be related to “designed in” flaws in the system, i.e. there may be fundamental design problems with the system that may not be possible to resolve through changes to operational practice. These design flaws can arise because of two factors: • an incomplete understanding of the backfill flow behaviour properties; and • limited knowledge regarding the hydraulic behav- iour of pipeline systems. This paper addresses these issues. BACKFILL DISTRIBUTION SYSTEM REQUIREMENTS Before addressing backfill flow behaviour and pipeline hydraulics, it is worth reviewing the requirements and expectations of a backfill distribu- tion system: • The system must operate in a reliable and safe manner and not expose mine personnel to opera- tional hazards. • The system must deliver the flow rate or tonnage to a number of different locations and levels within the mine. Typically, the distribution piping is extended as mining operations proceed and the delivery flow rate should remain within fairly nar- row limits. • The system should operate without any block- ages. • The piping system should not fail due to excessive pressures or worn piping. Importantly, the piping should wear at a predictable rate to enable the effective planning and execution of pipe replace- ment schedules. A well-designed system will meet these require- ments, with the proviso that the backfill quality is within the defined limits. 0% 2% 4% 6% 8% 10% 12% 14% 16% 18% 20% Pipeline Plug Borehole Plug Pipeline Burst Pipe Hammering Fill Sloughing Bulkhead Failure Fill Segregation Rat Holing Plugged Sump Other Percentage of Failures Distribution system Other causes Fig. 1. Canadian backfill failures (De Souza et al., 2003).