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RISING TO NEW HEIGHTS

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U.K.’s Lee Tunnel Progressing with Help of Potain Crane

On tunneling sites, cranes are as common as tunnel boring machines. They provide an efficient method to move material in and out of the hole. This selection of the proper crane is essential in ensuring the access shaft is not a bottleneck.

TBM asked Manitowoc, one of the leading crane manufacturers worldwide, to provide an example of the tunneling project utilizing a crane and the types of features that were needed. The example chosen was the Lee Tunnel for Thames Water in the United Kingdom, which marked the first use of a Potain MD 560 B crane in the country.

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Excavation work on £635 million ($980 million) Lee Tunnel is progressing well with the help of the crane, which is removing excavated soil from tunnel shafts and is scheduled to help with concreting later as the project progresses.

The Potain MD 560 B is Manitowoc’s largest top-slewing crane in the standard MD line. The crane on Lee Tunnel in London is the first in the country, and a team from Manitowoc Crane Care is overseeing all support for the crane from installation and erection to regular maintenance and monitoring.

Work on the project is demanding and continues around-the-clock to ensure the project stays on schedule.
Bernard Chatelet, plant manager for MVB, the joint venture contractor on the tunneling job, said there were two reasons for choosing the MD 560 B.

“First, it has great lifting capability, so we knew the MD560 B would be able to handle the loads we need to excavate,” he said. “Second, it has a powerful and fast winch. We need to complete the shafts before we can begin work on the tunnel itself, so it’s important to have a productive winch that will help us complete this part of the work on schedule.”

The Potain MD 560 B is working on the first stage of the tunnel, excavating material to create four 80-m deep shafts. To remove material for the shaft, which is mostly chalk and highly-abrasive flint, two small excavators sit inside the shaft and fill a skip with 20 t of soil which, combined with the skip weight, makes for a total load of 26 t. The MD 560 B removes and empties the skip, before returning it to the shaft for refilling.

The crane is working with four falls of wire rope giving it a maximum capacity of 40 t. The crane features a 250 LCC 100 hoist, which can reach speeds of up to 108 m per minute and is fitted with 500 m of cable.

In its current excavation role, working on the overflow shaft, the crane has a height of 32 m, although lifting heights will be over 100 m, as the shaft depth will eventually reach 80 m. For this work it has 50 m of jib. The crane will also work on the pumping shaft and its height will be increased to 46 m, while the jib will extend to 70 m.

Once the six-month excavation phase is complete, the MD 560 B will be used for concreting and other duties. There are two operators assigned permanently to the crane, each working a 12-hour shift five days a week. A third operator is on standby to cover in the event of an absence.

The 6.4 km Lee Tunnel will help capture 16 million t of sewage forced into the River Lee during heavy rainfalls. London’s sewers date from the 1800s and are simply not big enough to handle a city that continues to grow and also has covered areas of natural drainage in concrete. At 7 m, the tunnel’s diameter is wider than three of the capital city’s trademark double-decker buses.

The Lee Tunnel is one of three projects in Thames Water’s London Tideway Improvements program, designed to create a cleaner and healthier River Thames. The program also includes expanding Beckton Sewage Treatment Works by 60 percent to accommodate the increased volumes.

Construction began in September 2010, and tunneling work is expected to finish by the end of 2013. The whole project should be complete by 2015. The joint venture contractor, MVB, brings together construction companies Morgan Sindall, VINCI Construction Grands Projects and Bachy Soletanche.

Information for this article was supplied by Manitowoc.

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