CASE STUDIES Ӏ DECOMMISSIONING


MAMMOET DISMANTLES TWO TUNNEL BORING MACHINES USED ON HS2 PROJECT


Netherlands-based heavy lift and transportation specialist Mammoet has dismantled two tunnel boring machines used on the HS2 (High Speed Two) rail project in the UK.


Having previously supported Align JV (a


joint venture between infrastructure companies Bouygues Travaux Publics, VolkerFitzpatrick and Sir Robert McAlpine) with the assembly of two TBMs, Mammoet was well-placed to assess the requirements of the job. Assembly of the TBMs took place at Align’s


South Portal site, a large purpose-built site that included two factories that manufactured the segments required to line the tunnels, and a slurry treatment plant to process the spoil excavated from the tunnels. The dismantling of the TBMs was to take place at its North Portal site, near Great Missenden. Simon Crawley, senior commercial manager at Mammoet, visited the North Portal site to understand the different limitations relating to the dismantling – which obstructions existed on site and what space was available. “We determined that the equipment used to build the boring machines wasn’t necessarily the equipment needed for their dismantling,” said Crawley. “There were different limitations at the two sites. Because there were obstructions in the way, a 600t crawler crane was needed at the construction stage. We believed that a 400t crawler crane would be adequate to perform the dismantling.” To prove a lower capacity crane could do the job Crawley worked closely with Mammoet project manager Rhys Burley and the project engineer Antreas Michail to create a detailed visualisation of the project using Mammoet Move3D software. This included a full animation of the most complex lifts. Seeing how the job would be carried out using the smaller crane, Align was satisfied with the recommendations that Mammoet put forward and was able to use a more cost- effective solution. With separate TBMs creating the south


and northbound tunnels, two machines needed to be dismantled at the North Portal. The 400t capacity crawler crane (a CC2400) was used to remove the biggest components from the TBMs. For the heaviest component, the cutter head, an LR1300SX crawler crane was also used to perform a tandem lift. The components were lowered onto Mammoet Self-Propelled Modular


Transporters (SPMTs) before being taken to one of two laydown areas. Additional crawler cranes, including the LR1300SX and an LR1250 support crane, offloaded the components onto the ground or supports for further dismantling. As the cutter head was too heavy for the smaller cranes to lift, climbing jacks were used to offload it from SPMTs to the ground. A challenging aspect of the project was


the fact that the cutter head’s centre of gravity (COG) could not be fully known. The lifts also needed to be performed on a slight incline. This was because the TBMs exited the tunnel at an angle. Typically, challenges such as this this would result in having to create additional drawings and manage changes before performing the lift. This would add unnecessary delays, depending on how pronounced the differences were with respect to the original project planning.


The team instead came up with an engineering solution that would avoid unnecessary changes, and days or even weeks of potential downtime. “We used air hoists to make pneumatic length changes and keep the components level,” explains Burley. “It took away that manual element of hoisting chain blocks. It was done on a compressor rather than using manual labour, which was safer and more efficient.” “The key challenge was the large amount of equipment and people needed for the project,” concludes Crawley. “As the biggest global company when it comes to heavy lift and transport, we knew that we could meet these expectations. “We were able to offer a full turnkey


package, by providing all Mammoet personnel, all the crawler cranes, mobile cranes, SPMTs and jacking systems, and we could also adapt to any changes.”


CRANES TODAY 41


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