Construction World December 2016

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Civil Engineering Contractors

MAJUBA COAL SILO 20 RECOVERY PROJECT Majuba Power Station is in Mpumalanga situated between Volksrust and Amersfoort. It comprises Eight new 2 000 mm x 500 mm concrete columns to support the new shell were positioned around the outside circum- ference of the existing concrete and were excavated and dowelled into the existing foundation and extended to just above the existing openings.

The Majuba Silo Recovery Project was covered under Phase D – ‘Permanent Solution’. It involved the materials handling solution for the final stage to be developed in accordance with the results of the Silo 20 structural investigation process as well as the determination of the current conditions of Silo 10 and Silo 30. It was however expected that the plant configuration will return it to its original state. The project was carried out the Majuba Power Station Site and ongoing operations of the Power Station would take precedence over the construction work. The works included sectional completion in order to ensure that the coal supply to the power station was not disrupted during construction and commissioning of the works. The foundations, columns, transition slab, benching and 12 m height of existing shell was kept intact. The external face of the remaining existing concrete shell was cleaned (water power wash), checked and shear connectors were epoxied where required. About 1 m of the damaged top edge of the existing 350 thick shell was demolished, leaving the rebar exposed for incorporation in the re-cast benching. A 350 x 600 triangular edge beam had to be cast to the top edge of the benching to accommodate the new shell inside diameter. six units, Unit 1-3 each capable of providing 657 MW and unit 4-6 each capable of providing 713 MW. Majuba Power Station has been in operation since 1996 when the first unit was put into commercial operation. It is planned to operate until 2061.

The existing foundations, columns, transition slab, benching, existing shell and concrete roof were kept intact. The external face of the existing concrete shell (350 mm) was cleaned (water power wash), checked and shear connectors epoxied in. Six new 2 000 mm x 500 mm concrete columns and two composite steel columns, to support the new shell, were positioned around the circumference. The columns were dowelled into the existing foundation and extended to just above the existing openings. Thereafter a new 50 mm x 20,7 m internal diameter stiffening shell was constructed up to a height of 19 metres above the existing benching line. The shell was bonded to the existing shell by epoxied in shear connectors. A single formed slide technique was used to construct both silo 10 and 30. These were technically challenging as the slide started 12 m from NGL and were completed/finished 11 m below the existing top of silo. The formwork/sliding system during the assembly and stripping sequences were carefully engineered. The lift shaft is 5,39 x 5,2 m concrete box tower about 70 m high. The remaining portion of the existing lift shaft stub below ground level, was demolished while keeping the existing starter bars intact. Some additional starter bars had to be epoxied into the raft foundation. The 2 m raft foundation had to be excavated to expose the west face to allow the wall to be fixed to and cast against this face. The collapse of the silo was a significant event with major consequence on the power grid that caused serious power shortages. The successful execution of the project restored the operation of the power generation plant to full capacity. This obviously assists with the current power shortages and the impact it has on the economy.

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Project information • Company entering:

Stefanutti Stocks Civils Rula Consortium • Client: Eskom Majuba Power Station • Start date: 4 January 2016 • Project end date: 10 December 2016 • Main contractor: Stefanutti Stocks Civils Rula Consortium • Project manager: Eskom • Consulting engineer: Hatch Goba • Project value: R114 032 465

Construction WORLD

DECEMBER • 2016