The Ingula pumped storage scheme in South AfricaThe Ingula (previously Braamhoek) pumped storage scheme project, situated within the Drakensberg mountain range, on the border between the Free State and KwaZulu-Natal, will comprise an upper dam (Bedford) and a lower dam (Braamhoek), both of about 22 million cu m water capacity. The dams, located about 4.6 km apart, will be connected by underground waterways, through an underground powerhouse, which will house four 333 MW pump turbines, with a total capacity of 1,332 MW. During times of peak energy use, water will be released from the upper dam through the pump turbines to the lower dam to generate electricity. During times of low energy demand, the pump turbines are used to pump the water from the lower dam back to the upper dam. The construction of the project involves a number of separate civil engineering contracts, among which an exploration tunnel, a main access tunnel, access tunnels and an underground powerhouse complex. The station is planned to be fully operational by mid-2013. Click za/13.The waterways will include an intake structure for twin 6.6 m-diameter concrete-lined headrace tunnels, each with a length of 1,030 m, to the surge shafts (the main headrace surge shaft will have a diameter of 15 m). Twin inclined steel-lined pressure shafts of 5.1 m-diameter will lead into steel-lined penstocks of varying diameter. In turn, these bifurcate to two smaller penstocks leading to the inlet valves and the machine hall. They will have an overall length of just over 1,200 m to the main inlet valves, which are housed in the machine hall. The machine hall will have a length of 172 m, a height of 40 m, and an average width of 23 m. The adjoining transformer hall will be of similar length or longer (depending on the equipment needed), with a span of 18 m and a height of 17 m.In addition, there will be four 4.7 m-diameter draft tube tunnels, with a length of 135 m each, to reach the twin 20 m-diameter tailrace surge chambers. Two short 6.6-m diameter tailrace tunnels will lead to a single 9.4 m-diameter tailrace tunnel, in turn, leading to an outlet structure. This will be situated 2,530 m downstream of the surge chambers.The Braamhoek Consultants joint venture, consisting of Arcus Gibb, Knight Piésold and Stewart Scott, is responsible for design monitoring and supervision. Visit www.arcusgibb.co.za, www.knightpiesold.com and www.stewartscott.comExploratory tunnelThe building of the 858 m exploratory tunnel by Murray and Roberts began in 2005 andwas completed in June 2007. The 5 m x 5 m finished diameter horseshoe-shaped tunnel leads to the underground powerhouse complex. It was initially planned for investigating different types of support materials, exploratory drilling and for the installation and monitoring of instrumentation (incorporating convergence stations, extensometers, instrumented rockbolts, and rock anchors) to provide geotechnical data for design purposes. A Tamrock Minimatic 8087 twin-boom drill rig was employed from a single attack, with Mercedes-Benz 4 and 6 cu m dumpers serviced by Cat 950 G loader. The support consisted of self-anchoring bolts and fibre shotcrete using a Ramo shotcrete rig mounted on a Mercedes-Benz Unimog. Visit www.sandvik.com, www.cat.com and www.murrob.comMain underground worksA joint venture of Italy's CMC and local contractor PG Mavundla, has been awarded the main underground works contract, worth approximately EUR600 million. Visit www.cmc.coopDetailed design drawings are not yet available, but these works include low pressure headrace tunnels, surge shafts, inclined high pressure shafts, high pressure penstock tunnels and branches, machine and transformer halls, draft tubes, surge chambers and tailrace tunnels, busbar tunnels, control room, connecting and access tunnels, inclined cable shaft, shafts for dewatering and ventilation, access tunnels, adits for drainage bifurcation, anchor gallery works, etc. All excavations will take place in mudstones with dolerite dykes and sills, mostly using drill and blast but with some raise boring too. Support will consist of steel sets, fibre shotcrete and bolts and anchors. Rock haulage will be use loaders and dumpers. A conveyor system is under consideration but there is no firm plans as yet. These works have not started yet.Ongoing constructionThe main access tunnel contract, worth EUR19 million comprises 397 metres of 25 sq m construction access tunnels, completed in April 2008, and the main access tunnel, with 9 m x 8.7 m horseshoe-shaped cross-section (approx. 75 sq m) and a length of 1,274 m driven from one side. Work has already begun, with advance having reached 810 metres. It is scheduled for completion in the first half of 2009. The geology is mudrock with some dolerite intrusions and dykes. The excavation method is drilling and blasting, using a three-boom Atlas Copco XL3C jumbo using automatic laser positioning. Visit www.atlascopco.comThe ground is secured with Duraset grouted bolts, shotcrete reinforced with steel fibres applied with a CIFA Spritz System CSS-2 shotcrete robot. Suppliers of consumables for both the exploratory and main access tunnels include also Sika and BASF concrete admixtures, Maccaferri, Bekaert's Dramix fibres and Minova bolts. Visit www.duraset.com, www.cifa.com, www.sika.com/stm.htm, www.basf.com, www.maccaferri.com, www.bekaert.com and www.minova-ct.comSpoil and waste rock material resulting from the tunnelling process in the main access tunnel is transported by Cat 966G and 950G loaders, Bell B30D and B25D articulated trucks, as well as PowerStar 30 t dump trucks. At the construction access tunnels, a Cat 950 loader with Isuzu and Mercedes trucks were used. Visit www.bellequipment.comCMC and PG Mavundla will also build the underground powerhouse complex. Excavation method will be drill and blast in single crown heading to commence, slipe out each side then bench, using an Atlas Copco XL3C three-boom Boomer jumbo, with Cat 966G and 950G loaders to Bell B30D and B25D dumpers. Geology is mudstones with dolerite dykes and sills. Scaling will be performed with hydraulic breaker on Cat 320C. Support methods include typically 60 t 15 m and 30 t 11 m double corrosion protected bolts in the crown and 200 mm fibre shotcrete with mesh. Works have yet to commence but are due to start imminently. 32-33/08.