Progress at Chile's Chacayes hydro scheme
Progress at Chile's Chacayes hydro scheme Mar 2010
Report for TunnelTalk from Pacific Hydro
Since the devastating 8.8 earthquake at the end of February, aftershocks continue to rock southern Chile. Tunnels being constructed for the Chacayes hydropower scheme on the Alto Cachapoal River about 12km south of Santiago withstood the tremors well but work was suspended while damage to the construction powerline to the site was repaired. Work has since restarted and work for Pacific Hydro's 110 MW installation is progressing.

Fig 1. Plan of the elements of the project

The project consists of two intakes, one on each of the Cachapoal and Cipreses Rivers, 7km of canal, four separate tunnels ranging from 280m to 2.45km long, a 880,000m3 geomembrane lined re-regulation pond and a two unit surface powerhouse (Fig 1).
A consortium of Astaldi of Rome, Italy and local Chilean contractor Fe Grande (AFG) is undertaking the EPC contract. Andritz Hydro is supplying the electromechanical equipment. Notice to proceed was issued to the EPC (engineering, procurement and construction) contractor on May 20, 2009, but Pacific Hydro had previously undertaken extensive advanced infrastructure works including upgrading 32km of access roads to up to 10m wide, widening of an existing bridge over the Cachapoal River, construction of a 1,200-man camp for the workers and installation of a 17km 66 kV construction power line with three substations to feed the works.

TBM walks to Cipreses starter tunnel

Three of the tunnels are being excavated using conventional full-face drill+blast, using two-boom Atlas Copco and Tamrock jumbos and scoop trams. The exception is the 2.45km-long Cipreses diversion tunnel. Here AFG elected to use a refurbished 5.01m diameter Wirth TBM, primarily for schedule reasons. Excavation with the TBM started on 11 January, 2010 and the tunnel has advanced some 616m, with advances of up to 22m daily. Muck is being removed by a rail car system. Rock conditions have been generally good, but a fault running sub-parallel to the Cipreses tunnel resulted in water inflows of up to 160l/sec, which have since diminished. Geological risk has been assumed by the owner with daily sign-off on the excavation class of rock being tunnelled. Production risk is assumed by the contractor as well as the final lining of the tunnel.

Pressure shaft raise boring operation

The surge shaft and pressure shafts are being raised by subcontractor Bergteamet using a Tamrock Rhino 2006 raise borer. The drop shaft will be reamed to the full diameter of 5.5m, whereas the surge shaft will be reamed to a 2.5m diameter muck hole, and then slashed out to its final 8.5m diameter. By early March, the pilot hole of the pressure shaft has been completed and reaming had started.
Expected completion of all of the tunnels is September 2010, with the project scheduled to enter into service in July 2011.


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