Safari, A, Gasmier, M, Tennant, C & Jain, A 2026, 'Re-evaluation of gravity-fed backfill reticulation flushing using a water and 
compressed-air-assisted system in deep underground mines: a case study', in AB Fourie, M Horta, M Oliveira & S Wilson (eds), Paste 2026: Proceedings of the 28th International Conference on Paste, Thickened and Filtered Tailings, Australian Centre for Geomechanics, Perth, pp. 1-14, https://doi.org/10.36487/ACG_repo/2655_54
(https://papers.acg.uwa.edu.au/p/2655_54_Safari/)
Abstract: As underground mining operations extend to greater depths, cemented paste backfill (CPB) reticulation systems are increasingly subjected to operational conditions that diverge from their original design assumptions. One area significantly affected is the design of flushing systems, which are critical for maintaining flow reliability and preventing blockages. This paper presents a case study from the Gwalia gold mine in Western Australia where routine flushes failed to clear sections of the reticulation network below a certain mining level. This operation uses a gravity-fed CPB reticulation system with a nominal pipe diameter of 152mm and a plant flow rate of 140 m³/h. A detailed investigation combining field observations, hydraulic modelling, and air–water flow analysis revealed that the problem originated not from the air system performance, but from insufficient flushing water volume and flow velocity to sustain continuous flow through uphill sections. The study developed flow models using water as the base fluid to quantify minimum flushing volumes, pressure requirements, and air receiver capacities. Results indicated that approximately 21 m³ of water is required to initiate effective syphoning in the longest uphill section, while a 40 m³ air receiver, or 2 compressors, operating with a 14 m³ tank provide adequate air capacity for consistent flushing across the mine’s life. Based on these findings, design modifications including increased water supply capacity, adjusted flushing sequences, and recalibrated pressure systems were recommended to improve flushing efficiency and reliability. The study highlights the need to periodically re-evaluate CPB reticulation flushing systems as mine geometry evolves, ensuring continued performance under deep mining conditions.

Keywords: cemented paste backfill, design reticulation flushing, water and air flush