Modern Mining June 2019

POWER SUPPLY AND ENERGY EFFICIENCY

allowed construction of the weir to remain off the critical path and be implemented in parallel with the major civil structures.” Describing the river diversion strategy, the authors note that it comprised two stages of construction. “For Stage 1, a temporary embankment was constructed from the left bank of the river, upstream of the Intake Works. The cofferdam axis was also aligned to traverse over the exposed island section, before wrap- ping back downstream of the concrete intake structure footprint. The river could be main- tained in its natural channel right of the island, allowing for dewatering and construction of the entire hydropower works and the first 90 m of the permanent RMC diversion weir. “For Stage 2, an essentially mirrored cof- ferdam arrangement was applied, whereby the first stage embankment was deconstructed whilst a second embankment was initiated from the right bank of the river, aligned to abut against the completed portion of the permanent weir and terminating on a reinforced concrete crest splitter wall. During Stage 2, under nor- mal river flows, water was diverted leftwards into the intake structure and back to the river through the two 6 m wide by 4 m high sluice and scour radial gates. “Water could also be conveyed into the power canal, allowing turbine commissioning in the powerhouse to advance concurrently with the construction of the remaining portion of the permanent RMC diversion weir. During high flow periods, additional flood discharge capacity was afforded over the completed spill- way section of the permanent weir, constructed as part of the Stage 1 works.” It was originally envisaged that Azambi would be built using formal sector contrac- tors from the mine vendor list (including those involved in both the preceding hydropower schemes). After several rounds of negotiation, however, it was decided to award the the con- struction contract exclusively to Congolese construction enterprises, with the objective of uplifting and improving social economic status and promoting skills transfer. Two civil contractors were appointed as well as a dedicated steel fabricator and installer. The contractors had no previous experience of working on hydropower or large water retain- ing structures. This was regarded as a challenge and necessitated an intensified construction monitoring programme, focused on team col- laboration and risk management, to achieve the project’s production, quality and schedule requirements. A full-time Owners Team, who acted as the

overall project managers, undertook survey and managed the project budget. The team also assisted with contractors’ logistics plan- ning, equipment procurement and programme monitoring. South African subcontractors were engaged for certain specialist tasks such as pre- cision blasting and turbine installation. The contractor for the turbine installation, for exam- ple, was WD Power of Johannesburg, which also worked on the two preceding power stations. The authors note that strict compliance to quality, programming, safety and labour requirements were met and the major proj- ect milestones, including the two-phase river diversion implementation, were achieved. Safety performance was high and no serious injuries were recorded. The local labour force employed peaked at around 650 people. The Azambi project recently led to Knight Piésold receiving an Award of Merit in the Energy and Industry category of the Annual Awards for Engineering Excellence of the Association of Consulting Engineering Companies British Columbia (ACEC-BC). Commenting on the award, Sam Mottram, Managing Principal of Knight Piésold Canada, said: “The Azambi hydro-electric project dem- onstrates the effective use of Africa’s vast hydro potential to boost power reliability in remote areas, specifically for the mining industry and surrounding communities.” Azambi will produce approximately 64 GWh of renewable, reliable electricity each year to power Kibali. The useful life of the hydro station will likely extend beyond the mine’s LoM and could serve the communities as a legacy asset. Report compiled by Arthur Tassell photos courtesy of Barrick Gold

The Ambarau hydropower station. The second of Kibali’s hydropower projects, it was opened in 2017.

It was decided to award the the construction contract exclusively

to Congolese construction enterprises.

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June 2019  MODERN MINING  43