Independent peer review of a complex shaft design

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United Kingdom

Independent peer review of a complex shaft design

South African Icon
South Africa

Company

Major diversified mining company

Commodity

Polyhalite

Scope of work

Independent Review: Shaft Design

Challenges experienced

The Client’s aim is to produce fertiliser products, derived from Polyhalite, to sustainably aid the agriculture industry and grow more food. The Client has completed exploration drilling and has advanced the project towards shaft sinking. The Joint Ore Reserves Committee (JORC)-compliant resource estimate of this ambitious project stands at 2.66 billion tonnes of mineral resources and the project area spans 270 km² on-shore and 525 km² off-shore.

The mine infrastructure was designed to produce 13 million mineral tonnes per annum, which would increase with a second phase to 20 million tonnes per annum.

The following issues had to be addressed:
  • The design of a shaft lining that could withstand the exerted ground pressure posed a serious challenge.
  • The shaft lining should last 50 years without major repairs.
  • The sinking of the shaft will be conducted through creeping ground conditions and sandstone-derived water must be dealt with.
  • The client must comply with the environmental regulation that no mining infrastructure is visible above the treeline.
  • Additionally, environmental regulations stipulated that no transport to the mineral processing facility may commence above ground.

Approach to the solution

Fraser McGill conducted the independent peer review of this challenging shaft lining design. We assembled a highly specialized team, with the right mix of experience, to perform the review diligently. The Fraser McGill team consisted of a Structural Engineer, a Geotechnical Engineer, a Mining Engineer and a shaft sinking specialist with potash experience.

The Shaft headframe had to be lowered some 50 m below surface, from which a sub-bank level could be created. The sub-bank levels housed two vertical shafts that is 1,500 m deep. The basis of the shaft lining design was studied by the team and the current shaft lining stratigraphy was compared with previous designs and the different rock formations assessed. The various ground conditions were then compared with the specific shaft lining design. Special provision for dewatering was also studied for sinking through the creeping ground conditions of the Carnallitic Marl, Rot Salt and Halite seams.

To verify the shaft lining designer’s structural design, Fraser McGill staff performed various calculations, independent models and finite element analysis on the tubbing and other shaft lining structures.

The conventional underground room-and-pillar method was deemed satisfactory for the mineral resource. The sizing of the integrating tunnels was optimised for continuous miner equipment usage.

Furthermore, an underground mineral transport system was envisioned to transport minerals from the mine to the mineral processing facility 40 km away. The mineral transport system would be housed in a mining tunnel and consist of a conveyor belt, operational cables and services. Special provision was also required for a maintenance transit system.

Outcome experienced

  • To meet the Client’s timeline and save time, Fraser McGill was involved from day one and started the independent peer review before the final design was completed. The outcomes of the review could therefore be addressed in the ongoing design.
  • In addition to the comprehensive review, the client received regular technical notes on the shaft lining assessment progress. The designer’s geology dashboard and conceptual drawings were reviewed, and regular feedback given to the client alongside the ongoing work to complete the design review report.
  • Independent models and finite element analyses were performed to inform the Client and supplement the Designer’s work.
  • The Client and Fraser McGill Team worked together seamlessly despite being spread over several time zones across two continents.