Cajon del Maipo, 50 kilometers from Santiago de Chile, is a wild canyon of the Andean Mountains, overlooking the riverbed of the river with the same name. From the scenic point of view there is no comparison with the gentler and more touristy Valle del Maipo, famous for its hiking trails and great wine. In the harsher environment of Cajón, Aes Gener, Chile’s power generation and distribution company, is currently installing two hydroelectric power plants, which will produce a total of 531 MW, including three vertical shafts: the two 160 m high of Las Lajas (using penstocks made of S690 QL high yield structural steel with a diameter of 3700 mm) and the 600 m high of Alfalfal, (450 m penstock made also of S 690 QL diameter 2400 mm with a thickness up to 57 mm), one of the longest shafts in the hydroelectric industry.
It is a colossal job that required the experience and expertise of ATB Riva Calzoni, chosen by Strabag, the Austrian general contractor, for the construction of the penstocks. Last May the subsidiary, ATB Chile, was established to manage the job, hire local personnel and handle all logistical aspects. The penstocks, made of S690QL steel, a high-strength steel subject to high probability of cold cracking, are being constructed and once completed will be shipped to Valparaiso, not far from Santiago, and then transported overland across the country by ATB Chile. The intervention was divided into batches: the Hochtief Nuevo Maipo consortium, made up of Cmc and the German Hochtief, is constructing the tunnels upstream of the shafts, as well as the civil and underground works in the valley of the Yeso and Volcan rivers; Strabag alone is taking care of the second batch, which includes the shafts, the hall where the turbines will be located. The turbines will be supplied by Voith, as a third party contractor.
In August Chile will begin moving the equipment, which left the production plants in July. The worksite, which will be active 24 hours a day, 7 days a week, involves more than 220 people (at least 15% locals as stipulated by the contracts) with different expertise: engineers, human resource experts, accountants, lawyers, safety personnel, assemblers, welders, drivers, and technicians for non-destructive controls. The delivery of the works is scheduled for September 2018. But the real challenge is the installation and assembly of the shafts and penstocks: these huge “pipes” will be dropped into the vertical shafts and with a lift system, ATB Chile personnel will weld them with the utmost safety.
Davide Delpero, ATB Riva Calzoni engineer and project manager commented that “the engineering for this project has been quite demanding: the complexity is due to the geological conditions of the shafts and the type of rock our principal found during the drilling. The difficulties in the civil works forced us to modify the layout of the penstocks. It meant stopping each time to figure out which other way to go.” The climatic conditions will certainly complicate things in the execution phase. Mr. Delpero adds “The worksite is 1890 meters above sea level, so we will have to deal with the seasons: very hot in summer and very cold in winter.” Once in operation, the two Alto Maipo power plants will enable Chile and Peru to meet their energy needs.
