Chile has seen a number of tunnelling projects over the years and activity has been growing more recently with excavations in the hydro and road sector, and also a TBM in a mine.

Key projects of late, some still being excavated and others having already come into service, include the La Higuera, La Confluencia, Chacayes and Angostura hydro schemes as well as the San Cristobal toll road tunnel and copper mine development at Los Bronces.

What is notable of these recent projects is the presence of Australian, Norwegian, Italian, German and Brazilian firms in development of the projects. The companies range from energy utilities Pacific Hydro and SN Power to construction groups Astaldi, SELI, Impregilo, Hochtief, ACS Dragados and Queiroz Galvao Group.

Chilean companies involved are Tecsa and its Constructora Fe Grande unit.

A focus of interest among a number of the foreign firms also has been to help make the projects happen in the first place, and taking equity stakes, though some are focused on straight construction services. Hochtief and Astaldi, though, have done both.

La Confluencia & La Higuera
La Confluencia and La Higuera are sister hydro projects in the Tinguiririca river basin, about 150km south of Santiago, and they have involved significant tunnelling works. The projects have been developed by Pacific Hydro in co-operation with SN Power, now majority owned by Norwegian utility Statkraft. The utilities joint venture to develop and operate the projects is Tinguiririca Energia.

The turnkey civils contractor for La Confluencia is a 70:30 jv of Hochtief Construction and Tecsa. The 158-MW project was officially inaugurated at the end of last month. Turnkey civils works for La Higuera were performed by Constructora Queiroz Galvao Sucursal Chile SA, which is part of the Brazil’s Queiroz Galvao Group, and the 155-MW plant also recently came into service, though later than previously scheduled.

Upstream lies the La Confluencia project, which has two branch tunnels supplying waters from the Tinguiririca and the Portillo/Azufre rivers to a surface powerhouse. The discharged flows enter into the head of the La Higuera conveyance system.

There are three main tunnels across the two hydropower projects – the Tinguiririca and Portillo branch tunnels which are 9.3km and 11km long respectively, generally about 7m wide and excavated by drill and blast using six Sandvik jumbos; and, La Higuera’s dominant tunnel, which is a 5m diameter, almost 17.5km long transfer tube, also xcavated by drill and blast. In addition, upstream of each powerhouse is a surge shaft.

Chacayes
Development of the Chacayes hydropower project involves Pacific Hydro, once again, but this time with Astaldi as both an equity and construction partner.

The run-of-river scheme involves construction of a surge shaft and more than 6km of tunnels split into three sections – the Cipreses transfer tunnel, which taps the Cipreses River; two short transfer tunnels, including the Peralitas tube, part of a conveyance system including canals, culverts and a 2.6km long headrace tunnel running down the Cachapoal River to the surface powerhouse. The works are at a late advanced stage.

A jv between Astaldi (95 per cent) and Chilean firm Fe Grande was awarded an enginereing-procurement-construction (EPC) contract two years ago. Then in mid-2009, the year after Astaldi entered into a development agreement with Pacific Hydro to look at potential projects in the river basin, the Italian firm took a 27.3 per cent equity stake in the company undertaking the 111-MW development – Pacific Hydro Chacayes. The project is due to be completed next year.

Astaldi’s first entry to Chile was in the late 1980s with construction of tunnels on the Alfalfal hydro project on the Colorado River.

Los Bronces
For the Los Bronces copper mine, the owner, Anglo American Chile, wants to investigate how to optimise development of the deposit, and called upon TBM technology to do so.

The probe tunnel is being excavated by joint venture contractor Dragados-Belsaco using a 4.5m-diameter compact double-shield universal (DSU) machine, which was manufacturered by Seli to order for the mine owner. Slighly more than 8.1km of tunnel is to be bored at the Los Sulfatos prospect, over an estimated two years.

Seli’s simpler, shorter DSU shield with 27 (no.) 19-in. (483-mm) discs was launched in late 2009 from a cavern opened up by drill and blast. By the middle of last month the TBM had advanced 2716m with a best monthly progress rate of 363.5m (August). The following month progress was almost as good, at 351.9m.

The first 3150m of the drive is in quartz monzonite, to be followed by a short section of rhyodacite porphyry, 1300m of andesite and then other sequences.

San Cristobal
The 1.8km long twin tubes of San Cristobal toll road tunnel in the northern part of Santiago were opened to traffic over 2008-9 by the concessionaire on the public-private-partnership (PPP) scheme; a jv of Hochtief and ACS Dragados. Eight cross passages connect the tubes.

Tunnelling was performed by a combination of drill and blast and mechanical excavation for the 10m wide tubes. The bores holed through in 2007 and the first lining was completed and services installed the following year.

Construction work on the project was undertaken for the concessionaire by construction partners including Hochtief, ACS Dragados, Brotec and Belfi with Geocontrol as consultant.

The PPP concession was awarded in 2005, and Hochtief’s stake is held by Hochtief Concessions.

Angostura
The Angostura hydropower project is just getting underway in the Bio-Bio region, approximately 600km south of Santiago. The project involves excavation of diversion tunnels on the Bio Bio River and a large underground powerhouse.

In the second quarter, a jv of Impregilo with local firm Fe Grande was awarded a construction contract valued at approximately Euro 200M (USD 275M) by local utility Colbun to undertake the civil engineering works. The utility has a budget of USD 657M for the entire project, and it expects the 316MW plant to be completed by early 2013.

Impregilo said the award marked a return to the Chile while it has been already active elsewhere in Latin America, both on hydropower projects, and as part of a consortium to widen the Panama Canal.

Fe Grande is working on the Chacayes hydro project with Astaldi.

More Ahead
Hydropower is providing the majority of the tunnelling work in Chile at present, with a number of projects in development, including those under study by Astaldi along with Pacific Hydro.This may provide the Italian with both more construction and equity opportunities. While its compatriot has made a return to Chile, Impregilo remains on a construction-only focus.

Chile looks set to present both opportunities and further challenges for tunnellers in the next decade with the possibilities for further civils and underground works.


Map of some key recent and ongoing projects involving tunneling works in Chile Layout of the La Higuera and La Confluencia headrace tunnels Schematic of the separate Cipreses transfer tunnel and headrace on the Chacayes hydro project Finishing touches to a tunnel for the recently inaugurated La Confluencia hydropower project A 4.5m-diameter Seli compact TBM is driving an exploratory bore at Los Bronces copper mine