AGUAMILPA UNDERGROUND PENSTOCKS - EXCAVATION PHASE

The Aguamilpa hydroelectric project is one of a number of hydroelectri c schemes currently being constructed along the course of the Santiago River in western Mexico. Aguamilpa, with a total cost of $750 million U.S., is a 960 MW installation scheduled for operation by October 199 3. As the most important plant in the complex, Aguamilpa qualifies as one of the more spectacular engineering construction jobs of the decad e in Mexico. The facility is composed of a complex set of tunnels, inc luding the underground penstocks, the powerhouse and surge chamber cav erns, the tailrace tunnel, and temporary tunnels. In the initial desig n, most of the tunnelling work was to have been of a permanent nature. However, as the date of completion was brought forward, it became nec essary to open up more working faces and as such a number of temporary tunnels were started. This paper presents the sequences of undergroun d penstocks excavation, the construction methods developed, and the eq uipment employed. Also, the complex patterns of tunnels that were dril led initially for access and to facilitate later excavation of the und erground penstocks are described.