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Rio’s largest urban mobility project is competing for the highest honor in tunneling. The unprecedented tunnel excavation system used on Line 4 of the Rio de Janeiro Subway is among the finalists of the ITA Tunnelling Awards 2016 – the world’s foremost awards in the tunnel industry – in the category Technical Innovation of the Year. 

The system is designed to assure that the work was carried out safely, without affecting the densely populated neighborhoods of Ipanema and Leblon, in the city’s South Zone.  With this system, it was possible to build the 5.2-km tunnel in the substratum composed of a mixture of sand and rock. The new methods developed by Brazilian engineers resulted in a work with no expropriations, and reduced impacts on the surface.

Engineers from Construtora Norberto Odebrecht, who submitted the project to the Awards, will compete in this category with professionals from Singapore, Finland, Norway, and the UK. This year, the ITA Tunnelling Awards received 98 entries from 25 countries. The 33 finalists are divided into nine categories. Winners will be announced during a ceremony to be held in Singapore on November 11. On Monday (9/12), the project will be presented at a technical Congress in Buenos Aires, Argentina.

The main innovation was the creation of an unprecedented system for excavation in sandy soil. The team of engineers developed an additional system specifically for soil conditioning, thereby showing that it is possible to use a hybrid Tunnel Boring Machine EPB (Earth Pressure Balance) in sandy soil efficiently and safely. The alternative method would be to use a Slurry-type tunneling machine, generally used in sandy soils, but such a system would increase the risk of severe settlement in the ground, which would be inadequate in a region with so many buildings.

“For the first time in the world, we used an EPB in sandy soil in a densely built region, with heavy circulation of people and vehicles. Prior to this project, the machine had only been used twice in this type of soil, but only in short stretches and in unpopulated or sparsely populated areas. To perform the job, we created an internal system to inject different types of materials for soil conditioning during excavation, such as a foam polymer custom-designed for the subsoil in the South Zone of Rio. This increased the operating capacity of the EPB machine in sand, for the first time advancing its operation into the area of the Slurry machine,” explained Júlio Pierri, engineer from Construtora Norberto Odebrecht and Engineering coordinator for Line 4 of the Rio de Janeiro subway. 

In the development of this new tunnel-digging technique, Pierri worked alongside engineers Alexandre Mahfuz and Carlos Henrique Turolla, also from Construtora Norberto Odebrecht, with the support of the MTC consulting firm. “It was a huge challenge.  We had to dig the tunnel under the street beds without passing under any buildings, and with the lowest possible risk of settlement for the edifications, which in some stretches were only 12 meters from the tunnel. The solution was to develop a specific model for the region,” added Mahfouz. 

The hybrid EPB enabled the engineers to work with pressure control in front of the machine and minimize the possibility of settlements on the surface and surrounding buildings, as well as provide a considerable reduction in the volume of materials used in soil conditioning and energy consumption. The application of this technology also allowed for a reduction of the equipment operation support area, particularly in a densely urbanized area of the city. 

Using the Hybrid EPB (known locally as Tatuzão, or “Big Armadillo”), it was possible to traverse a complex geology efficiently and safely, reducing risks of instability. The terrain of the tunnels included a long stretch of beach sand bordered by two sections of highly abrasive rock. The custom-built machine weighed 2,700 metric tons and measured 123 meters long and 11.5 meters in diameter, the equivalent of a four-story building, and is the largest such machine ever used in Latin America.

The Award

Considered the ‘Oscar’ of tunnellers, the award is given by the International Tunnelling and Underground Space Association (ITA). This is the second edition of the ITA Tunnelling Awards, which received entries of 98 jobs from 25 countries, in nine categories. In all, there are 33 finalists, five in the same category as the Rio Subway - Line 4. The job is the only Brazilian project vying for this category in 2016. Another Brazilian project is a finalist in the ITA Tunnelling Awards 2016, but in the category Young Tunneller of the Year.