Inland Branch - Site Visit: Sasol Shondoni Colliery Project
The Inland Branch of the Concrete Society recently hosted a site visit to the Sasol Shondoni Colliery project near Secunda. More than 40 members attended this fascinating project, which features two large coal bunkers of 15 000 tons and 4 000 tons ‘live’ capacity and the foundation for a 22 km overland conveyor for transporting the coal to the Sasol gasification plant in Secunda.
On hand to welcome the visitors, and provide presentations, were Francois Vermeulen representing the contractors Stefanutti Stocks, Lyonell Fliss, Consulting Engineer of Lyonell Fliss & Associates, Krzystoff Szymczak Consulting Engineer of Logiman, Louw van Heerden from the client - Sasol Mining . Before proceeding to the bunker site, guests were given a broad overview of the project, including such aspects as the concept, design, engineering and construction.
Concrete was chosen as the preferred construction material for the bunkers as well as for the foundations as being the most advantageous compared with other materials such as steel, and reinforced earth. It was viewed as superior in terms of cost, durability, technical performance, ease of operation and maintenance.
The precast concrete option, rather than in-situ concrete was chosen for the bunkers due to a number of advantages, all of which were realised during the construction phase, namely:
- Vastly improved constructability
- Superior durability (abrasion and corrosion resistance)
- Improved discharge flow
- Safer construction with less labour at heights
- Shorter construction duration
- Cost savings
The 15 000 ton bunker, the main focus of the visit, measures 76 metres long by 20,5 metres wide and 28 metres high. It has 10 bays, each of 7,5 metres span.
On top of the bunker is a steel beam grid which supports a feeding tripper conveyor enclosed in a structural steel house. A reclaim conveyor run beneath the bunker, under a stockpile in a tunnel and then discharges coal into the overland conveyor.
The foundation, columns and end and internal partition walls were constructed in in-situ concrete as they were easier to shutter, reinforce and cast. The deck beams, sloped bunker slabs and beams, and vertical walls were precast, avoiding any scaffolding which is would have been required for casting in-situ of such elements.
The precast and in-situ elements are fully structurally integrated into the “composite” structure through monolithic in-situ concrete connections and in places, by pre-stressing, thus using the full structural capacity of all elements.
The overland conveyor is 22 km long, on a 3D curved route with a transport capacity of 2 000 tons per hour. The conveyor belt is supported on idlers on more than 6 000 structural steel frames at 3 metre centres which are in turn supported on sleeper foundations based on light precast sleepers and augured ‘minipiles’.
This system proved to be more stable and durable than the use of conventional gravity sleepers.
During the visit to the bunker site, Roelof Jacobs, Inland Branch Chairman took the opportunity to thank all the stakeholders involved in approving and arranging the event. He also thanked Hanlie Turner, National Vice-President of the Concrete Society for initiating the concept of visiting this remarkable project.
He hoped, he expressed, that all those present had learnt a great deal from the experience and that they would continue to support the Society at similar future visits.