Robbins TBM Overcomes High Overburden at OlmosThe coast of Peru is a barren scrubland which proves fantastically bountiful when water is brought to it. And, for centuries, the problem of how to bring the abundant waters on the Amazon side of the Andes to the Pacific coast has perplexed engineers. The Andes are an immense barrier that prevents rain from moving from the jungle regions of northeast Peru and Brazil toward the dry coast. The vision of conveying water from the Atlantic side of the mountains to the fertile but dry Pacific side has enticed Peruvian leaders from one administration to the next. It was only after the government of Alejandro Toledo relaunched the Olmos trans-Andean project on the basis of a design-build-operate, public-private partnership (PPP) concession, and enlarged it with a hydroelectric component in 2001, that the current, promising effort took shape. The tunnel dates back to the 1920s, with several attempts made in the 1950s using drill-and-blast techniques.When complete, the tunnel will be part of a system to annually transfer more than two billion cubic metres of water from the wet to the dry side of the mountains. The project includes damming the Huancabamba river near the village of San Felipe with the 43 m-high, roller-compacted concrete Limon dam to form an impoundment reservoir. Water will then be diverted through the mountains to the usually dry Olmos river on the Pacific side. The first phase, which involves construction of the dam, excavating the tunnel, moving a gas pipeline and building an access road, is under way. Later phases will include construction of at least two more drill-and-blast tunnels and two more dams, as well as an extensive canal system on the Pacific side to distribute the water on the coast. Two hydroelectric generation facilities capable of generating 600 MW are also planned.The Olmos hydropower and irrigation project is located in the region of Lambayeque, approximately 900 km to Lima, in the northwestern part of Peru. Concesionaria Trasvase Olmos is responsible for the implementation of the water transfer and construction firm Odebrecht is in charge of its construction. Construction activities involve the departments of Lambayeque, Piura and Cajamarca. The eastern jobsite is located in San Felipe (Cajamarca), where the Limon dam is under construction and where is also the trans-Andean tunnel entrance. The western site is in the Salas district (Lambayeque), where the Quebrada Lajas tunnel and the exit of the trans-Andean tunnel are located. The TBM, which excavates the remaining 13.8 km section to connect with the eastern face, was launched from the western side. The tunnel's east entrance is 1,085 metres above sea level. Project componentsThe Olmos trans-Andean tunnel stretches for 21.6 km and consists of a 331 m 3.5 m-diameter steel-lined duct (almost completed), a 1,900 m access tunnel (nearly finished), the 1,132 m final inlet tunnel (concluded), the eastern entrance (2,837 m, almost concluded), the western exit (1,502 m, almost concluded) and, between the two, the 13.8 km tunnel driven by TBM. The project also entails several other structures: the 43 m-high Limon dam, the 26 m-high 5 m-diameter provisional inlet tower (concluded), a 107 m-high surge shaft, a 163 m divertion tunnel (concluded) and the 520 m Quebrada Lajas tunnel.Project playersThe project owner is a company named Proyecto Especial Olmos Tinajones (PEOT). General contractor Concesionaria Trasvase Olmos, which is comprised solely of the Brazilian engineering and construction firm Odebrecht, won a 20-year build and operate concession from the Peruvian government and Lambayeque regional government in July 2004. Today, Odebrecht Perú Ingeniería y Construcción is working on the massive irrigation project that will dam the Huancabamba river on the western side of the northern Peruvian Andes and then funnel the water through the mountains to the dry Olmos riverbed. To do this a 21.6 km-long tunnel is being bored through the continental divide. Click pe/17. Visit www.peot.gob.pe and www.odebrecht.com.pe or www.odebrecht.comConsortium Supervisión Olmos, led by Coyne et Bellier with Lahmeyer and Alpha Consult, is responsible for the project supervision. Visit www.coyne-et-bellier.fr, www.liperu.com and www.alphaconsult.com.pe Tunnelling methodsThe final inlet tunnel features a 24.3 sq m excavated, unlined cross-section. The divertion tunnel has a 161 sq m excavated cross-section, whereof 36 square metres will be lined. The Quebrada Lajas tunnel is characterised by an 18.1 sq m excavated cross-section, whereof 1.75 square metres lined (invert and benches). These three tunnels were excavated using drilling and blasting, employing a two-boom Tamrock Axera D06 jumbo to excavate the first two and a two-boom Atlas Copco Boomer H 128 for the Quebrada Lajas tunnel. Sandvik supplied the cutting tools and Exsa the explosives. Visit www.miningandconstruction.sandvik.com, www.atlascopco.com and www.exsa.com.peThe rock from the divertion tunnel and the final inlet tunnel is removed by a Volvo L90 loader at each face (one per tunnel) and four Scania P360 conventional trucks per drive. Reinforcement consists of anchoring bolts, welded mesh, fibre-reinforced shotcrete and H6" ring beams. Visit www.volvo.com/constructionequipment/na/en-us/products and www.scania.comStanding up to the pressure, a 5.3 m-diameter Robbins unshielded main beam TBM is boring a 13.8 km-long tunnel through the Andes, beneath hard, potentially squeezing rock. The machine is working in complex geology consisting of quartz porphyry, andesite, and tuff from 60 to 225 MPa UCS. Over 400 fault lines are present along the entire tunnel, including two major fault lines approximately 50 m wide. Click here.Although the TBM is tunnelling through one of the lowest reaches of the Andes, it is still one of the deepest tunnelling projects in the world with 1,931 metres of overburden at its deepest point. It is bested by only the Gotthard base tunnel in Switzerland, which withstands an overburden of 2,251 metres. Visit www.therobbinscompany.comThe overburden has created another problem: high in-tunnel temperature, predicted to exceed 54°C. To cope with the high temperature, Robbins has designed the machine with a unique ventilation and air cooling system. Two interacting systems are being used to cool the tunnel to 32°C or below. The high jobsite elevation (1,080 m) results in less dense air and less heat transfer capacity per cubic metre of air, so the two systems will make it possible to blow more air into the tunnel for a maximum cooling effect. The TBM, named "Pachamama" which means "Mother Earth" in the local Quechan language, is 320 m long and weighs 220 tonnes. Crews are installing rock support behind the head to ensure the tunnel's stability throughout construction. The TBM is equipped to install rockbolts supplied by Aceros Arequipa, wire mesh of Industria de Fortificación Minera, fibre-reinforced shotcrete (Sika is the provider of the fibres as well as the concrete admixtures) and U6" and H4" ring beams, made at the site and installed according to the type of rock encountered, to secure the cut as it progresses, as well as precast concrete segments for the floor of the tunnel only. The invert segment moulds have been designed by Odebrecht Perú Ingeniería y Construcción and made by Construction Engineering Management & Procure Technology (Cempro Tech). The gaskets are supplied by Acero Importaciones y Representaciones. Visit www.acerosarequipa.com, http://formin.galeon.com/index.html, www.sika.com.pe or www.sika.com, www.cemprotech.com and www.aceroimpor.comRock removal work is performed by 36 Mühlhäuser muck cars pulled by four Schöma diesel locos (model CFL-180 DCL). The rock is removed by a conveyor belt and two trains (while one is cruising out of the tunnel, the other is being loaded). Click here. Visit www.tunnelling-equipment.com and www.schoema-locos.de Work advanceConstruction of the Olmos water transfer commenced on 23rd March, 2005 and will be concluded on 23rd March, 2010. The TBM was launched in March 2007 by subcontractor Odebrecht. The Robbins machine has overcome not only tough geological conditions but also unpredictable weather. Last spring, La Niña rains inundated the northern Peruvian coast bringing the project to a month-long halt. The TBM lost power on 1st April and, soon after, a thick layer of mud and debris washed out the only access road leading to the construction area. Work was not able to resume until 28th April. Despite delays in December 2007 due to bursting rock and the nearly one-month delay of last spring, the machine is still on schedule for a projected finish of its 13.8 km journey in March 2009. The machine is now averaging 3.2 m per hour, advancing roughly 22 m per day. In July, the machine achieved production rates of up to 38.3 m per day. It is operated in two 12-hour shifts with a 4- to 6-hour downtime between shifts for maintenance and probe drilling. As of 30th July, the TBM had excavated 5,658 metres. In July, the machine achieved a total of 650 metres. As of 21st August, the TBM had advanced 6,130 metres. To date, 13.4 kilometres of the Olmos tunnel has been excavated, whereof 6.22 kilometres had already been excavated before the award of the concession and the remainder (1.8 km) excavated or to be excavated by drill-and-blast methods.By March 2010, the first phase of the tunnel project will be operational and will supply more than two billion cubic metres of water annually for irrigation of 560 square kilometres of farmland. View a slideshow at www.kleph.com/Slideshows/olmos/index.html 36/08.