The Hyperloop aims to connect cities around the globe. To connect the whole of Europe and expand the Hyperloop network, the infrastructure of the Hyperloop should not only cross land but also seas. Looking at the proposed network by the Hyperloop team of TU Delft, there are a few routes crossing water in Europe. For these routes the current idea is boring tunnels under the seabed. But this has some disadvantages: High costs and slow tunnelling speed. Alternatives are explored to reduce costs and increase tunnelling speed.

The route between Stockholm and Helsinki crosses at least 200 km of ocean. In a typical week a tunnel boring machine can move through 100 m of clay, taking around 40 years just to finish the construction of the tunnel.[1]* Elon Musk hopes to be able to go 14 times faster as the current boring machines, due to technologies developed by “the Boring Company”. [2] This still has to be proven and even if it will be possible, the construction of the tunnel would still take 3 years. To make crossing the sea by Hyperloop more realistic, a substitution of tunnelling should be thought of. Allseas has a lot of experience laying steel pipes on the seabed used for gas and oil. And with their methods in previous projects they have proven to reach average velocities of 5 km/day. [3] The Hyperloop tube can be seen as a simple steel pipe, therefore Allseas has investigated the possibility of laying the Hyperloop tubes with the current pipe lay methods. 

Figure 1: S-Lay principle

Allseas lays pipelines on the seabed with a method called S-lay. The S refers to the shape which the pipeline takes from leaving the vessel until touching the seabed, illustrated with the red line in the figure above. The vessel is a factory where smaller pieces of pipe (called joints) are connected to the pipeline leaving the vessel step by step. The first part of the pipe leaving the vessel is supported by a structure called the ‘stinger’, ensuring that the stresses and strains in the pipe will not exceed their limits. Compared to the current pipelines the biggest challenge of installing a Hyperloop tube is the significantly larger diameter. The Pioneering Spirit is the leading vessel in the pipe lay industry and can currently lay pipelines with a diameter up to 1.72 m (68”). This is significantly smaller than the 3.5 m diameter of the current Hyperloop design. In cooperation with the Delft Hyperloop team Allseas has looked into a suitable diameter for S-lay. Considering the necessary passenger comfort, the minimum required inner diameter of the Hyperloop tube equals 2.5 m. For this dimension a steel wall thickness of 5cm and an extra concrete layer of 18cm is necessary to ensure that the pipe does not collapse due to the water pressure and that the pipe will not float after installation. Initial estimates from Allseas show that when the necessary adjustments on the vessel are done, a lay speed of 1 km/day could be reached. Thus, decreasing the construction time of the route Stockholm to Helsinki from 42 years to only 200 days, making it more attractive.

Unfortunately every solution also brings some extra challenges that should be thought of. Where safety is already a big challenge on land, creating safety exits under water will be even more difficult. The Eurotunnel connecting France and the United Kingdom dealt with this problem by building an extra tunnel to which people can be evacuated. This can also be applied to the Hyperloop by laying an extra pipe. This solution will come with extra costs.

Lastly, current estimations show a price of almost 19 million euros per kilometre** for steel only. Making steel by far the biggest contributor to the total costs. Therefore the challenge is not only to make it technically possible but also to make it economically feasible due to the thick steel wall thickness. This leads to the next step of the research: the optimization of the pipe. By decreasing the weight of the pipe without losing its strength the costs can be reduced significantly, making the idea of crossing the sea by Hyperloop a realistic prospect for the future.   

By Allseas (Niek Verbruggen & Carmen Petsch), September 2019

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* When boring with one tunnel boring machine at the time
** These costs are calculated for a unidirectional steel pipe



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