Murray & Roberts has formed a joint venture with Hochtief of Germany and Jäger Bau GmbH in preparation for the tender for the main underground works for Eskom’s Ingula (formerly Braamhoek) Pumped Storage Scheme (PSS) about 60km outside Ladysmith in KwaZulu-Natal. The tender for the five-year contract closes in September, after which it will enter an adjudication process.

Hochtief is an international multi-disciplinary civil engineering company with a speciality in tunnelling and underground excavation. It has executed a number of major projects in South Africa to date, including the Ngqura deep-water harbour project near Port Elizabeth in the Eastern Cape, the Durban Harbour Services Tunnel, and as a major partner in the Lesotho Highlands Water Project.

Jäger Bau GmbH also specialises in the construction of underground works from tunnels to hydro-electric schemes. The company has executed numerous international hydropower, water irrigation and infrastructure projects in Africa, Europe, Latin America and Asia.

“Murray & Roberts Cementation is the local mining partner of this JV, along with Concor Holdings and Murray & Roberts Construction as the local civil engineering partner. Together we make up a very strong team encompassing all the necessary skills to deliver this project successfully,” Allan Widlake, Murray & Roberts Cementation business development director, says.

The main works of the Ingula PSS comprise a multi-billion-rand project that will rank as one of the most challenging projects ever undertaken in South Africa. It will involve 1.09 million m³ of underground excavation, 58,000m³ of shotcrete, 256,000 roof bolts of various sizes, and spoil excavation (surface) of 1.7 million m³.

Murray & Roberts Cementation, in conjunction with Concor Holdings, which was acquired by the Murray & Roberts Group in October 2006, completed the exploration tunnel of the Ingula PSS in June 2007. This 1,050m long tunnel, with a 25m cross-section, was mined with a twin-boom drill rig. The mechanised equipment set-up comprised a cat wheel loader for mucking into standard tipper trucks, a roof bolter for roof support, a Rambo shotcrete pump mounted on a Unimog vehicle and emulsified explosives for blasting.

A concrete blinding was placed on the roadway floor to provide good footwall conditions up to the face. A separate dedicated batch plant supplied both shotcrete for support purposes and concrete for the roadway footwall. The tunnel wall was covered with a 100mm thick layer comprising two layers of steel fibre reinforced and one layer of normal wet concrete. Roof bolts of 4.2m and 3m in length were used, comprising 25mm full-column resin roof bolts. The exploration tunnel has a 7.1° inclination.

Commenting on the challenges associated with the project, contracts manager Kobus Nortier says that the project location, on the edge of the Drakensberg escarpment, entailed winds of up to 140kph and huge swings in rainfall. Being an environmentally sensitive site, Murray & Roberts Cementation had to adhere to strict regulations pertaining to waste handling and water recycling.

“We have accumulated a lot of knowledge with regard to the site conditions, which stands us in good stead to clinch the contract for the main underground works. We completed the exploration tunnel in 24 months, with minimal lost-time injuries or incidents in that period,” Nortier says.

Widlake explains that the Ingula PSS comprises two dams, one at the top of the Drakensberg escarpment and the other at the bottom, together with underground waterways, an underground powerhouse complex with four turbines, access tunnels and access roads.

The powerhouse complex chamber is 180m long, 24m wide and 54m at its deepest point. “This large underground excavation will represent a significant achievement for the JV,” Nortier says. When the national electricity grid has surplus capacity, the turbines are transformed into pumps to replenish the topmost dam.

The completed exploration tunnel will carry all the high-tension cables from the underground powerhouse complex. Being the first tunnel on the entire project, it was fitted with such instrumentation as convergence stations and instrumented rock bolts in order to obtain the necessary geotechnical information to verify the designs of the consulting engineers.

“We are confident that the extensive experience we have garnered on this project to date, together with the international companies we are partnering with will provide us with the leading edge in securing the remainder of the work on the project. We are ideally positioned to provide the client with a total solution in terms of skills and capacity,” Widlake concludes.

The name Ingula refers to the creamy contents at the top of a milk calabash, according to Eskom. This pumped-storage scheme will have a generating capacity of 1,330MW. It will be a peaking station that will be used mainly when there is a peak in the electricity demand. The first unit is expected to be commissioned in 2011.