Works at the Millares power station began in October 1998 and, despite their complexity, given that this was an underground plant situated below the level of the Tous reservoir, it joined the network in the second half of last year, as scheduled. The new hydroelectric power station, which has a net head of 123 metres, makes use of much of the existing civil works: the headwater reservoir of El Naranjero, the water connection, the underground channel covering a length of 13 kilometres and the loading tank, capable of holding up to 70,000 m3, meaning a minimum effect on the environment during the works process and subsequent use. In fact, the other constructed installations have all been underground, except the small generating facilities that interconnect with another already existing system of 138 kV. The Millares power station is located in a cavern parallel to the course of the river Júcar, just 110 metres into the solid rock. The limestone nature of the location has meant that filter-proof concrete structures had to be constructed that were able to support a pressure level equivalent to an immersion of 70 metres.
The project consisted of transferring two pipes with a diameter of 3.2 m into a pipe with a diameter of 4.40 m, in a round cavern with a diameter of 5 m, in which they are connected by means of conical transitions (truncated cones). The Technical Department of ULMA Construcción proposed a solution for concreting in three stages: sill, gables and ceiling. However, in the end, only one stage was carried out for time reasons.The formwork had to have a resistant base of HM Beams and braces which would be lined with wooden trusses and boards, supported by props and OC Shoring.
