Conveyor drives for rapid transit tunnel construction in central London

The metropolis London is currently adding a new East-West rapid transit connection with a length of more than 100 km to its much-frequented public transport network. For this major project, 21 km of new tunnels are being bored in the city centre alone. The soil here mainly consists of soft clay with a sticky consistency that makes the transport of excavated material especially challenging. H+E Logistik and Nord Drivesystems, two German industry specialists, are supplying suitable conveying technology including geared motors.

Named after the mathematician Ada Lovelace and the city map pioneer Phyllis Pearsall, Ada and Phyllis are tunnel boring machines (TBMs) from German manufacturer Herrenknecht, each measuring approximately 100 m in length and weighing about 1,000 tonnes.

Working for the rapid transit project "London Crossrail", they have been pushing forward their 7 m wide "Cutterhead" blades below the City since 2012. After tackling the distance of six and a half kilometres between Royal Oak and Farringdon Station, they are planned to resurface in 2015. Besides Ada and Phyllis, more TBMs are currently boring similar tunnels in various other track sections for the East-West connection through London which will measure a total of 118 km. The first Crossrail sections will be put into operation in 2018. With an investment volume of more than 17 billion EUR, "London Crossrail" is currently Europe's largest infrastructure project.

Demanding Transportation Task

The TBMs excavate up to 1,300 tonnes of "London clay" per hour in the two 6.2 m diameter tunnels that are being bored in parallel below the city center. The handling of this soft material does require solutions that are tailored to its consistency. In this case, the challenge lies in reliably transporting the excavated material away from the building site, which includes routing it over machine, tunnel, and hall conveyors before loading it onto trains.

State-of-the-art tunneling includes the addition of tensides to the excavated material directly at the boring machines in order to facilitate handling. However, if the special London clay formation and these additives came into contact with standard conveyors, complications would soon arise: the mass would promptly and persistently stick to parts of the conveyor belts. Tunnel conveyors for the "London Crossrail" project were therefore custom-tailored by the Herrenknecht subsidiary H+E Logistik. In addition to special plastic coatings and other measures, a wiper system developed especially for the on-site requirements serves to prevent problems caused by conveyed material sticking to exposed system components.

Firstly: Reliable. Secondly: Versatile

Specifying and procuring reliable conveying drive technology proved similarly important. H+E Logistik approached its proven partner, Nord Drivesystems from Bargteheide near Hamburg: "We have been cooperating with Nord for approximately ten years now, and have tackled hundreds of projects together", says Dirk Uphues, the H+E project manager in charge of the London operation. "The reliability of geared motors on our conveyors has always been a decisive factor. Nord fulfills this key requirement, no matter which drive type they deliver for us."

For the London tunnel conveyors, Nord supplies helical bevel geared motors with a double-sided, smooth output shaft. An expansion coupling transfers the torque to the belt conveyor. "Of course we would like to minimize the drive variety, and the double-sided shaft allows for the versatility that we need: our systems typically complete not only a single tunneling project, but are often bought back on completion for other tasks. With a variable drive configuration, they can more easily be used in different locations", says Uphues.

Seamlessly and Without Delay

All Nord gearbox housings are manufactured using a single piece construction with no joints or seams. This applies even to very powerful industrial gear units up to 242 kNm, which are required for extreme conveyor inclines and moving very large amounts of conveyed material. The one-piece Unicase housings of Nord's industrial gear units feature integrated bearing seats. Thus, there are no sealing surfaces between the drive side and the gearbox housing that are susceptible to damage through torque and radial forces.

With its offset bearing shaft arrangement, the Unicase design also ensures very compact dimensions but allows for the use of larger bearings for higher loads and extended working life. Industrial gear units can be installed as left or right side conveyor drives. Most types are globally available with fast delivery times. Even though tunneling projects can take many years, customers like H+E Logistik appreciate suppliers who can ensure short-term availability.

Besides tunneling, the London Crossrail project also includes the remodeling of existing stations and the construction of new ones. Some time ago, additional manual excavation work that could not be planned in advance near Bond Street Station was scheduled on short notice. So as not to affect other project deadlines, H+E was tasked with providing suitable short conveyors within eight weeks. "The required drive technology from Nord arrived five days after ordering," says Birgit Barian from the H+E purchasing department. "Particularly when a project is nearing completion, you can easily find yourself in a situation with tight delivery deadlines and considerable time pressure. Even if you have kept all of your own deadlines, many third party problems and sometimes unforeseen circumstances come into play. Without partners like NORD, that are available virtually on demand, you might easily find yourself in difficulty."

(Nord Drivesystems develops, produces and sells drive technologies with around 2,800 employees, and is one of the international leaders in the industry. In addition to standard drives, the company supplies application-specific concepts and solutions, even for special applications, for example with energy-saving drives or explosion-protected systems. It produces a wide variety of drive units for torques from 10 to 200,000 Nm, electric motors with powers from 0.12 kW to 200 kW as well as the necessary power electronics in the form of frequency inverters and servo controllers. Inverter solutions are available for classical installations in the switch cabinet and for decentralised and fully integrated drive units.

Getriebebau NORD GmbH & Co KG, Germany/NORD Drivesystems Pvt Ltd, Pune. Email: Joerg.Niermann@nord.com, jyoti.mishra@nord.com)