The pressurised headrace tunnel is 4100m long, 12m wide and 10m high. Vattenfall was responsible for the tunnel design as well as the geological examinations for the construction. The breakthrough was reached on September 25, 2010.
“The rock cover is between 100 and 350m and it is not possible to make a detailed examination of the geological conditions,” said Gunnar Frostberg, Project Manager. “It is always a challenge to construct a tunnel in a complex geology as the one we have here in Changuinola.”
The rock is composed partly of limestone, partly of volcanic and sedimentary rock types. Before water filling of the tunnel can take place the final rock support of the tunnel perimeter will be completed with additional spraying concrete and rock bolts where needed.
Other features of the Changuinola project include a 100m high RCC dam, 40m high power intake, powerhouse with two Francis turbines with a total capacity of 213MW and a switchyard. A 10MW mini hydropower plant is also being built at the dam toe.
The power station is expected to be in operation in mid 2011.
