Herrenknecht technology and expertise is breaking new ground on a challenging tunnelling project through tough rock in Norway.
Norway is a country with infrastructure rich in tunnels; however, until recently, tunnelling projects in the Scandinavian region have relied on the traditional drill and blast method, using explosives to deal with the extremely hard indigenous rock and limiting tunnelling technology to smaller hydropower projects.
Herrenknecht technology is revolutionising the tunnelling landscape on the Follo Line Railway Project in the country’s capital, Oslo, where – in a world first – tunnel boring machines (TBMs) are being used to excavate through tough and most abrasive rock, gneiss. The project, for Norwegian rail company Bane NOR, will remove 4 million m3 of rock to create twin 20 km tunnels from the municipality of Ski to Oslo.
“Probably no state has more tunnels than Norway,” says Bane NOR Project Manager Anne Kalager.
“For every inhabitant, statistically there are 1.3 meters.”
During site visits, Bane NOR’s Geologist Agnethe Hoff Finnøy shows guests the palm-sized chunks of rock that result from the four TBMs’ operations, which began in 2016, explaining the significance and effectiveness of the process.
“Gneiss is a particularly hard rock,” says Ms Hoff Finnøy.
“The TBMs crack the hard rock into chips like this. It works wonderfully.”
Changing with the times
There were a number of factors to consider when it came to selecting a construction methodology. The drill and blast method traditionally used in Norway would have required seven jobsites – some of them located in metropolitan areas – which would have been difficult for trucks to access.
Ms Kalager says it is important for the industry to keep up with advances in technology, in order to provide the best possible options for the communities impacted by construction that will continue over years.
“If we want to stay fit for the future we can’t just say: we’ll do it the way we’ve always done it. We must always keep looking for the best methods – and as it turns out, in this project TBMs have decisive advantages,” she says.
“So drill and blast tunnelling would have meant a huge burden on the traffic and the many residents living near the jobsites.”
In contrast to the drill and blast method, using a TBM requires only one central jobsite well away from residents, which provides easy vehicle access as it is linked directly to the highway. Two 900 m access tunnels connect the jobsite on the surface with two underground caverns, where the TBMs can commence tunnelling north and south.
“All these advantages were decisive for the TBM solution,” says Ms Kalager.
Progress in harsh conditions
According to the project timeline, the railway line is scheduled to be operational in 2021; in order for works to completed, the TBMs must achieve breakthrough in both tunnels by the end of 2018. Acciona–Ghella Joint Venture (JV) Project Director Fernando Vara carefully monitors the daily and nightly progress of the machines, receiving a report on the night shift’s progress each morning.
“So in the first minute after waking up I can see if the day is going to be stressful,” Mr Vara says.
“Ten rings are good when the geology is difficult, but 14 or 15 rings are normal.”
The 9.9 m diameter double shield TBMs simultaneously bore and line the tunnel with 1.8 m wide reinforced concrete rings. In order to achieve an average advance of 27 m/d through rock with a compressive strength of up to 300 MPa, Herrenknecht has equipped each of the machines with 13 engines, providing 475 horsepower for each drive of the 265 t cutter head.
The extreme toughness of the rock and geology can cause a number of difficulties that can result in slower progress. Sometimes the rock in front of the cutter head contains fissures filled with groundwater, which requires the team on the next shift to inject a liquid cement mass to displace the water.
Maintaining the machines
The strong vibrations and abrasive rock cause heavy wear to the cutter discs; to ensure that optimum use can be achieved by each 19 inch (483 mm) diameter disc, Herrenknecht manufactured each disc of special steel.
Over the course of the project, more than 6,000 cutter discs will be changed on each machine and transported to Herrenknecht’s Schwanau plant where they are completely overhauled. Herrenknecht Project Engineer Luis Cuartero is responsible for the cutter management in Oslo.
“In close cooperation with our customers we feel our way ever closer to the optimal parameters for the disc cutters,” says Mr Cuartero.
“We improve details on the bearing and try out the effects of different lubricants and seals.”
Mr Cuartero also ensures that strict maintenance procedures are followed for each of the TBMs, including making sure the hoses of the hydraulic circuits, electrical components, and engines and pumps are in good condition.
“It’s in everyone’s interest that the machines are kept in the best possible condition over the entire distance of the drive. That’s why we are so attentive, and sometimes suggest sensible preventive maintenance to the customer on the basis of experience.”
Impacting the future
Norway has a long history of tunnelling using drill and blast methods, while smaller TBMs and microtunnel boring machines had previously only been used on smaller projects.
Ms Kalager says this project – and the assessment and analysis used for its planning – has expanded the potential for greater use of tunnelling technologies in the region, expecting that it will as a signal for further tunnelling projects in Norway.
“In future TBMs will be a realistic alternative in large projects, even in our extreme hard rock,” she says.
This article was featured in the Summer edition of Trenchless International. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
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