Designed in PTC Creo, eight 1,000-ton units are cutting through 26 miles of widely varying conditions.
For years the Crossrail project has been burrowing tunnels for a new rail line directly under London. More than 26 miles in total have been carved out by gargantuan tunnel boring machines (TBMs), purpose built for Crossrail by German firm Herrenknecht. Each unit costs around £10 million ($15 million), weigh close to 1,000 tons, have an external diameter of 7.1 metres (23 feet) and from cutting-face-to-end stretch 150 meters (500 feet).
Today, three years after its May 2012 start, tunnelling is almost complete. Deep beneath the streets of East London, the project’s final two TBMs, Victoria and Elizabeth, are approaching their final destination. When they do, they will complete a process that has seen eight separate machines painstakingly thread their way beneath the heart of one of the world’s busiest cities.
The Herrenknecht units, designed in PTC Creo, use the earth pressure balance process invented in Japan in the 1970s. Each TBM compacts extracted material (known as spoil by the diggers) to a pressure which equals that of the surrounding soil and groundwater. Pressure balance is constantly monitored by the TBM driver, who can regulate it by either adjusting the speed of the TBM through the earth or the speed of the conveyor which takes spoil away from the carving head.
As the machine moves ahead, 3,000 kilogram pre-cast concrete segments are hoisted into place. More than 250,000 such segments will be placed by the time the tunnelling phase is completed later this year. The process moves along 24 hours a day, 7 days a week. Rotating crews of 15 members each run the operation. A typical 12-hour shift can burrow 16 meters of tunnel.