Tunnel construction: metro projects and mega-machines

The global expansion of metro and rail infrastructure has been driving a boom in tunnel construction for years. New metro systems are being built in major cities, existing lines are being extended and more and more transport infrastructure is moving underground. At InnoTrans, Herrenknecht demonstrates the technical scale this development has now reached.

The company is one of the world’s best-known manufacturers of tunnel boring machines and believes the industry is currently in an exceptionally dynamic phase. There is talk of a ‘golden age’ of tunnelling at the exhibition stand. In fact, more major tunnelling projects are currently underway worldwide than ever before – ranging from urban metro expansion to transnational rail links. What is particularly striking is the international nature of the business. Projects in Europe, Asia or the Middle East differ considerably in terms of geology and infrastructure. Consequently, the machines are not mass-produced but are individually developed systems for specific construction projects.

Herrenknecht develops one-off tunnel boring machines

Tunnel boring machines are among the most complex specialised machines in the infrastructure construction sector. Each machine is tailored to the geological conditions and requirements of a project. According to Herrenknecht, this is precisely where a key factor for success lies. Among other things, the exhibition stand will feature a model of a tunnel boring machine used on the Crossrail project in London. The machine bored tunnel tubes beneath the River Thames – right through the heart of one of Europe’s most densely populated cities. The design of the cutter head is particularly important here. It must be precisely adapted to the ground conditions. In the case of London, ‘London Clay’ played a decisive role – a clayey subsoil that poses special challenges for excavation and material transport. The cutter head carries various tools:

• Cutting teeth for removing soil
• Cutter discs for breaking up harder rock
• Fluid systems for removing the material
• Protected shield designs for soft ground
• Segment technology for constructing the tunnel tube

Machines with a diameter of 18 metres

The scale of modern tunnel boring technology is impressive even to industry experts. The model on display at the trade fair has a diameter of seven metres. By contrast, the largest machines built to date reach almost 18 metres and are considered world record holders. Behind the actual cutting head, there are also extensive trailing systems. These can be between 120 and 400 metres long and handle supply, logistics and material transport. Particularly in long tunnel projects, this infrastructure determines efficiency and construction speed. Building materials, tools and so-called rolling stock units are transported into and out of the tunnel via the trailing systems. Despite the enormous technical scale, staffing requirements remain relatively manageable. According to Herrenknecht, operating a tunnel boring machine typically requires around 20 specialised staff. In addition, electricians and hydraulics experts support operations to keep the systems running smoothly.

Asia and the Middle East are driving the market

The market is currently growing particularly strongly in the Asia-Pacific region. China, in particular, has been investing heavily in metro and rail infrastructure for years. Herrenknecht points to more than 600 projects in the last ten years alone. The Middle East is now also one of the most important growth markets. Cities and states there are investing heavily in new metro systems and underground transport infrastructure. One example of this is the metro project in Doha. In the early 2010s, Qatar decided to build a large-scale tunnel network. For the first phase of construction, Herrenknecht supplied a total of 21 tunnel boring machines. The scale of the project was extraordinary:

• 112 kilometres of new tunnel sections
• 21 tunnel boring machines
• 20 machines in operation simultaneously
• Completed in just 26 months
• Entry in the Guinness Book of Records

Gotthard and Crossrail as major European projects

Europe is also currently experiencing a new phase of major infrastructure projects. The Gotthard Base Tunnel in Switzerland is regarded as one of the best-known examples of modern tunnelling technology. Herrenknecht was involved in this project with tunnel boring machines. The tunnel was even opened earlier than originally planned. Another flagship project is Crossrail in London. There, two large tunnel tubes were constructed right across the city. The aim was to relieve pressure on local transport and improve regional infrastructure. Such projects highlight just how important tunnelling has become for growing cities. Above-ground transport systems are reaching their capacity limits in many places. Underground solutions create additional space without having to make major changes to existing urban structures.

Competition and technology transfer are on the rise

International competition in tunnelling has changed significantly in recent years. Whilst Western manufacturers from Europe and North America used to dominate the market, Chinese competitors are now increasingly entering the fray. Herrenknecht views this development as a normal part of global competition. Technology transfer can hardly be completely prevented in an international industry. What is therefore crucial is the ability to remain faster and more innovative than the competition. At the same time, German engineering remains in demand for many major projects. According to the company, the demand for German mechanical engineering expertise played a particularly important role in the Doha metro project. This reveals a pattern in tunnelling that is characteristic of many major industrial sectors: competition is becoming more international, projects are getting bigger and technical requirements are becoming more complex. For manufacturers of tunnel boring machines, this means continuous development – and a market that continues to grow worldwide.