Paterson & Cooke (P&C) has led paste backfill engineering for more than three decades. From its origins in South Africa in 1991, the firm has grown into a specialist group in slurry transport, independent test work, tailings management, long-distance pipelines, and backfill systems. P&C has a global reputation for designing integrated paste backfill systems from surface to underground. Its recent work at MMG Khoemacau’s Zone 5 operation in Botswana demonstrates the importance of independent test work and an integrated approach to design, system control and implementation for a safe and reliable paste backfill system.
Paste Backfill Requirements for the Zone 5 Underground Copper Mine
The underground copper mine at Zone 5 requires paste backfill to enable full recovery. The orebody extends 3 km on strike, with three mining corridors and long paste reticulation distances on surface and underground. As mining progresses on retreat, high strength paste is required to maintain extraction ratios and stope turnaround efficiency. P&C was responsible for the design of the full system from surface paste plant to the underground reticulation and backfill management, taking the project from feasibility through to implementation.
Paste Plant Design and Surface Pumping Infrastructure
Tailings are dewatered at the Boseto concentrator, hauled to Zone 5 and fed into the paste plant. The paste plant consists of three modules, located in the middle of the orebody, with a design flow rate of 150 m³/h each. Positive displacement (PD) piston pumps deliver paste through DN200 piping to the mining declines with a paste backbone reticulation via borehole.
High-Pressure Paste Pumping and Pipeline System Design
Given the long surface delivery distances, a high-pressure pumping system operating up to 150 bar was required. Dedicated high-pressure flush pumps provide redundancy and controlled flushing and pressurisation capacity in case of blockages. Due to the high‑pressure and full‑flow design implemented to reduce the wear on the boreholes, both steady state and transient hydraulic modelling was performed to define the safe operating window and keep pressures within acceptable limits.
Transient Hydraulic Modelling in Paste Backfill Systems
While steady state modelling defines baseline flows and sizing, it does not capture the time dependent behaviour of a modern paste system. Transient events such as pump trips, pipeline filling, blockages, rupture disc bursts, and rapid valve closure can generate short pressure surges exceeding the values predicted by steady state analysis. If not managed, these pressures can surpass design limits and damage supports, valves and piping, and more importantly put operators at risk.
Transient modelling captures these effects and guides mitigation measures such as pipe specification, support design, rupture disc sizing, dampener selection and safe operating protocols emphasising the importance of the “surface-to-underground” design philosophy.
Surface-to-Underground Paste Backfill System Integration
For Zone 5 P&C completed the entire detailed system design from surface foundations to the stope. This included a transient analysis to define peak pressures and forces, and to inform the selection of pressure relief devices, anchor design, and the underground piping layout. The analysis supports a control philosophy with permissives, interlocks, automated sequences and flushing modes to maintain safe operation. The approach reflects lessons learned from international operations where inadequate transient management caused support failures, excessive pipe movement or coupling fatigue.
Binder Testing and Optimisation for Ultra-Fine Tailings
The system design was further informed by a comprehensive binder testing programme for the ultra‑fine tailings produced at Boseto. Ordinary Portland cement and blended cements incorporating various supplementary cementitious materials such as ground granulated blast-furnace slag and fly ash were evaluated for early and long term (up to 360 days) strength.
The results guided the commercial binder selection, and importantly, a commercial adjudication informed by supplier-specific cement performance. This established a base case for supplier product performance comparison and improved binder consumption forecasting.
Integrated Engineering for Reliable Paste Backfill Operation
The Zone 5 project illustrates the importance integrated paste backfill system design by a specialist such as P&C, where process design, independent test work, binder optimisation, hydraulic modelling, transient analysis and controls form a single package. P&C’s involvement across all stages of the project, from test work to commissioning, local operator training and operations support, ensures a fully integrated, reliable system from surface to underground.
The Growing Role of Specialist Backfill Engineering
As mines target higher extraction ratios tighter production schedules, backfill consulting is increasingly a multidisciplinary specialist role that adds value up front rather than generalist engineering done as an afterthought. Paterson & Cooke support clients globally with the specialist expertise to design and operate safe, high-performance paste backfill systems.
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View the full original article in International Mining January 2026
MSc Engineering (Civil), BSc Engineering (Civil)
Bruno is a director at our Cape Town office in South Africa. He leads the African mine backfill department and has completed projects from conceptual level through to detailed engineering, implementation, and commissioning.
Bruno’s postgraduate studies focussed on cement chemistry, and he now specialises in its application to backfill. He is part of the Paterson & Cooke Backfill Group and is involved globally with problematic backfill applications related to geochemistry and cement chemistry.