In Chile, the huge Alto Maipo hydroelectric dam project on the Rio Maipo will supply the nearby capital Santiago with energy. The power plant with a capacity of 530 MW was planned around 10 years ago and is currently the largest construction project in the country.
European construction group Strabag, based in Vienna, Austria, was awarded a first partial contract for the construction of the power plant in November 2012. It is located about 50 km southeast of Santiago in San José de Maipo in the province of Cordillera.
The project includes the construction of tunnels with a total length of 74 km. These tunnels will carry the water not only from the Rio Maipo but also from the Colorado River to the turbines. The elevation range of the construction site alone is considerable, ranging from 820 to 2,500 m above sea level.
In order to deliver absolutely reliable work in this strategically important construction phase, those responsible decided to use underground machines from German manufacturer GHH, among others. During the initial negotiation for the use of 12 GHH MK-A20 dump trucks, for tunnel construction with a conventional drilling and blasting method, the criteria used by Strabag to make the purchase was based on the reputation of this machine. “Strabag already has used them in other projects around the world, a reputation acquired through the robustness, simplicity and reliability demonstrated by this model.” Subsequently the project progressed and the fleet was increased to 28 units of this model, also adding a LHD loader model LF-10, four mixers TM05 and one shotcreter IS26.
This project has also generated a strategic alliance between Strabag and GHH in aftersales areas, such as technical assistance in the field, consulting, machinery repair and component repair, amongst others. Two caverns alone saw extraction of more than 40,000 m³ of material each. Three hard rock TBMs, one double shield TBM and two simple shield TBMs were used, providing for about 40 km of tunnelling.
A total of three million cubic metres of excavated material were moved. “Here the GHHs performed magnificently: no severe failures were recorded. The manufacturer attributes this to the particularly robust, reliable and – in the best sense – simple design of the articulated dump trucks: all relevant components are easily accessible for maintenance.”
The MK-A20 can carry 20 t or up to 12.5 m3 of hard or soft rock and has an operating weight of 18.96 t. The vehicles are around 9.4 m long and a maximum of 2.2 m wide, with an overall height of around 2.5 m. At GHH they represent a medium-sized model used in both mining and tunnelling applications – the manufacturer also has larger variants up to the 35 t class MK-A35.
The Alto Maipo project is scheduled for completion in the summer of 2022. “For the dump trucks in use, this will probably not be the end of their lives: many of them will be used on other construction sites after they have been refurbished. Only recently, a similar vehicle returned to the manufacturer’s factory for overhaul after it has not been used for five years at a remote site – only the battery had to be replaced.”