A 4.56 m Robbins Double Shield tunnel boring machine (TBM) has been launched in Andean Mountains, Chile, where it has already completed large sections of a 12 km intake tunnel as part of the Los Condores Hydroelectric Project (HEPP).
The Los Condores HEPP, which is located 360 km south of Chile’s capital Santiago, includes the construction of a new 150 MW power plant and intake tunnel. The Robbins Double Shield TBM is boring two sections of the intake tunnel, the first measuring 6 km and the second measuring 4.4 km.
A section between the two tunnels will be excavated using the drill and blast method, connecting the tunnels and extending the overall length to approximately 12 km in length. Tunnel Production Manager Pello Idigoras from Ferrovial Agroman, who is responsible for the delivery of civil engineering works on project, said that the plant will provide much needed electricity to people across Chile.
“This project brings an increase in energy production in the country, thus contributing to the overall improvement in the welfare of its citizens,” said Mr Idigoras.
The location of the construction site – consisting of a high cover and hard rock – is no doubt the biggest challenges facing the contractors. The site has 500 m of hard rock cover and tunnelling operation are being completed some 2,500 m above sea level.
The journey to launch the machine was another difficulty, requiring shipment of the machine’s components and vehicle transport on unsealed, mountainous roads in Chile’s Maule Region. Mr Idigoras said the contractor was aware of the challenges associated with the location of the jobsite prior to the machine’s launch.
“The location of the work is a big constraint due to its rugged terrain and geographical location in the Andes. With all this, we are anxious to perform work in an efficient manner,” he said.
The TBM is boring through sedimentary and volcanic rock. The rock has been tested at strengths up to 100 MPa UCS, with at least two fault zones, the first of which has already been crossed in rhyolite, andesite, tuff, and breccia.
Mr Idigoras said that, for the most part, the conditions are suited to double shield tunnelling, although there are areas of challenging ground. To cope with the conditions, which includes increasing water inflows at rates of up to 3,500 litres per minute, the contractor is using cementitious grouting and chemical grouting with polyurethane and foam.
TBM supplier Robbins had anticipated the contractor would use ground conditioning techniques, and as a result designed the machine to effectively apply such techniques.
As the TBM excavates, it is lining the tunnel with 250 mm thick, 1.2 m long concrete segments, in a four plus one arrangement, and is currently progressing at a rate of up to 1.25 rings per hour of boring. Crews are operating in two 10 hour shifts, with 4 hours per day dedicated to maintenance.
As of January 2017, the 4.56 m Robbins Double Shield TBM had completed boring on the 900 m long access tunnel, as well as having made considerable progress on the first section of the headrace tunnel. It has excavated over 1,300 m of tunnel since it was launched on 27 May 2016.
Mr Idigoras says the TBMs performance and the completion of the access tunnels are huge milestones on the project; however, there is still work to be done.
“After many months working in engineering, manufacturing, installation, and commissioning, we are proud to see this result. It would be impossible to name all the people who participated in this project thus far but they, as a whole, have managed to get the TBM started digging and boring well,” he said.
For more information visit the Robbins website.
This article was featured in the Spring 2017 edition of Trenchless International. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
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