The underground solutions seminar at London’s Institute of Civil Engineers kicked off with a lively presentation by Colin Eddie, managing director at UnPS. He looked at innovation over the last 20 years – including much brought to market by UnPS – current state-of- the-art techniques and technology and also at new materials and construction methods on the horizon.

Eddie said that the tunnelling sector was well placed to help achieve some global sustainable development goals, including gender equality; clean water and sanitation; industry innovation and infrastructure; sustainable cities and communities; responsible consumption and production; and climate action.

He added that these goals were all the more critical as pressure increased on infrastructure and on society generally. “The global trend is towards increased urbanisation in developing countries,” said Eddie, adding that the world population is predicted to rise from 7.3 billion (in 2015) to nearly 10 billion by 2030.

“This creates cities with insufficient shelter and insufficient infrastructure and services.”

Overcrowded transportation systems, inadequate water supplies and sanitation and increasing pollution were all potential results of urbanisation, he said.

As ‘explosive’ urbanisation continued, Eddie said the scale of tunnelling projects was also increasing and the global underground market value is currently close to USD 2tr (the UK’s current underground market value is USD 60bn). But, he said, infrastructure costs are too high – particularly in the UK and current technologies are “literally stone age, scratching the ground”.

Technological progress

Eddie recapped on a similar presentation he gave 10 years ago, touching on technology advances that had varying degrees of success in being brought to market.

Of these he mentioned the “truly remarkable” UltraShell lining, formed from a passive smart self-healing engineered cement composite, and the concept of using microwaves to break through rocks.

“How close are we to this?” he asked, adding that improved cutting tools could cause a paradigm shift in tunnelling. Significant research, including by TBM manufacturers, is going on the field of microwave, water jet and laser cutting. Eddie quoted Anglo American mining group as saying it believed it would be cutting rock with laser tools in the next 10 years.

Eddie also looked at the concept of sustainable high-speed travel. The Swissmetro tunnel was being discussed 10 years ago, he said, but the futuristic project using vactrain technology went into liquidation in 2009 due to lack of support.

Nuclear-powered TBMs also came under the spotlight, with Eddie saying that Rolls Royce believes that portable nuclear reactors are 10 years from market.

“The US invested in research at the Los Alamos Scientific Laboratory of the University of California 10 years ago. A lot of people probably ridiculed it at the time but the science is upon us to make this work. The US Department of Energy was developing SSTAR [small, sealed, transportable, autonomous reactor], a portable reactor that has an operational life of 30 years without refuelling. Military and civil marine vessels are powered by nuclear energy, so why not TBMs?”

Eddie said other developments were on the closer horizon, including in the area of small freight delivery tunnel systems. “Cities like London are crying out for more efficient freight delivery systems,” he said, adding that UnPS is working with MoleSolutions and Arup to bring the first freight capsule tunnel to Southampton.

The Hyperloop concept also came up for discussion and Eddie is adamant the technology will be realized “In May 2016 the French railways SNCF invested EUR 80M (USD 85M) into a 700mph (1,100kph) intercity super tube train which could make HS2 obsolete before it is built,” said Eddie. “Arup is all over it because they know it can work.”

Hyperloop has also signed a deal to link Dubai with Abu Dhabi, reducing the travel time from an hour to just 12 minutes. “This is real,” said Eddie. “It’s going to happen.”

Eddie also looked at the benefits of extruded linings using a high-performance fibre reinforced material, which he said had the potential to revolutionise high speed tunnelling. “Industry based R&D programmes are required to eliminate current problems but, again, this will happen,” he said.

The righT fibres

Steel fibre reinforcement is moving on from something that simply improves the concrete and towards improving the rebar – it’s not just about durability but is now adding a structural dimension.

This was covered by two Bekaert speakers. Benoit de Rivaz presented the company’s latest steel fibre – Dramix 5D – while Hendrik Thooft introduced the eyeD System, which is the company’s new online measuring device for Dramix.

De Rivaz made the point that reinforcement fibres came in all shapes, sizes and materials and that there was no good or bad product but that it was important to get “the right product for the right use”.

He added that while the development from Dramix 3D to 4D was evolution, the development of the 5D fibre was more “revolution” because of the different way it works. “It opens up new opportunities in structural requirements,” he said.

Dramix 5D fibres were used in the Lee Tunnel in Beckton, London. The project included five shafts connected by a 7m-diameter, 7km-long tunnel. The Dramix 5D steel fibre reinforced concrete (SFRC) for the slip-formed tunnel lining took 18 months to develop. The five shafts were also designed and constructed using an innovative slipformed type of shaft construction, which also incorporated SFRC. This substantially reduced the quantity of structural reinforcement, thus enabling a faster and safer construction process.

SFRC may have been around for decades but it is still a new concept for some designers “and it freaks them out”, said Hendrik Thooft.

“There is caution among some contractors and consultants because they need reassurance that the fibres are really there and that they are distributed properly.”

This quality assurance could be provided by Bekaert’s new eyeD System, which has been brought to market and is already in use in Europe.

The eyeD device is a real-time measuring tool that analyses the homogeneity (not the number) of the steel fibres in the concrete mix as it flows through the chute of the concrete mixer. That data then transmits via 3G, 4G or WiFi to a tablet or smartphone for real-time monitoring and also to a central server.

“The eyeD weighs 25kg and can be operated by one person,” said Thooft. “It is easy to operate and attaches simply to the chute of the concrete mixer with hooking cables – it is compatible with most chutes on the market. It is battery powered and has about eight hours of battery operating life.”

Technical advantages include continuous measurement of the complete batch of concrete; immediate access to data, enabling speedy corrective action as required; full traceability of the measured data; elimination of “human error”; cloud storage of data; privacy of measured data; full reporting on compliance with the job site specification; and certainty that the reinforcement is in the right place.

Thooft said certain fibres could incorporate RFID markers, thus providing “full traceability” and that while at present the eyeD just measured the ambient temperature, they could add the functionality to measure the temperature of the concrete.

Five eyeD devices are currently available to rent and will be operated exclusively by quality control companies who will be trained in its use by Bekaert. It is only compatible with Dramix fibres. “If other fibres are used it will work but it won’t store the data on the server,” said Thooft, adding, “the eyeD is not a gimmick – it should be part of the whole quality control plan”.

Sealing and protection

Vincent van de Vrie of Trelleborg Engineered Products presented a paper on polymer solutions for tunnels, which outlined the company’s sealing and vibration-damping products for bore and immersed tunnels. These include the Gina Profile, which is designed for immersed tunnels and has a 120-year life and the Omega Seal, which is the company’s primary product.

Van de Vrie also outlined the design possibilities of the company’s Waterstop, which ensures a water-tight seal between construction joints, and four types of tunnel segment gaskets – glue in, slotted hydrophilic, co-extruded hydrophilic and cast-in. Michael Uebigau from Agru spoke on the merits of concrete protection liners, which provide separation against water seepage and pressing ground water. He highlighted his company’s Agruflux tunnel liner, which is made of very flexible polythene and has a very high degree of resistance to chemicals. It’s also suitable for use in water protection areas where clean drinking water is involved.

Promat’s Paul Sparrow drew delegates’ attention to the importance of incorporating fire protection measures in tunnels. More than 300 tunnels are protected with Promat’s board systems and more than 1.5 million square metres of structural linings are protected with its spray system.

He said that preserving life by providing emergency exits and visual and audio warnings was one thing but Promat was also concerned with protecting the asset. He added that he was extremely sceptical of claims by manufacturers of water-based fire suppression systems (WBFSS) or fixed fire fighting systems (FFFS) – basically sprinkler or deluge systems – that they could also protect the structure.

“These methods are only as good as the activation system, whether it’s manual or automated,” said Sparrow. “The two main issues are reliability, including the risk of lack of maintenance once the tunnel is handed over to the owner; and the availability of components after some years have passed.”

The alternative, he said, is passive fire protection. “It doesn’t need power, water or human intervention to operate and it doesn’t need turning on or off. A significant number of tunnels now have passive fire protection, so it has proven resilience.” Sparrow’s presentation brought home the speed at which fires can take hold in tunnels – an increasing risk as tunnel lengths increase – but also that freight considered by many to be non-hazardous could be anything but benign.

For example, 41 people lost their lives in the Mont Blanc tunnel fire in 1999, which was caused when nine tons of margarine and 12 tons of flour ignited.

The tunnel was closed for five days and the income loss was estimated at EUR 450M (USD 475M).

Sparrow also noted the EUR 600M (USD 638M) cost of the Channel Tunnel fire in 1996, adding that Promat had quoted for a GBP 26M (USD 32M) system to protect the tunnel against fire but it wasn’t taken up because “a risk assessment deemed it unnecessary”.

At 1,200 degrees Celsius most building materials disintegrate and melt and even rock tunnel starts to spall. Concrete expands, loses strength and stiffness and collapses in fires and factors affecting explosive spalling include heating rate; the exposure element of the fire; moisture content; the porosity of the concrete; the age of the concrete; the aggregate type and size; and the cover to the reinforcement.

Sparrow made the point that every tunnel has to be treated as a separate case because no concrete is the same. For example, calcareous aggregate retains heat for longer.

“We must design for the worst case scenarios, not the best,” he said. “We don’t know what or how much will be passing through these tunnels in 100 years time so it’s important that we take time out to consider the risks and protect those assets.” Protection of assets could be a description of RamArch, a system developed for Network Rail by Innovative Support Systems Ltd and described at the seminar by David Hindle. The system, which, put simply, combines galvanised steel mesh and reinforced concrete, “looks like old fashioned technology”, said Hindle. “Network Rail has a lot of old brick tunnels and brick delamination causes a lot of problems. They needed a system to give them a quick fix but that was adaptable to a permanent fix.”

The system comprises a simple reinforcement weld mesh in a square pattern. The mesh is manufactured in panels, which are then deformed to form a ridge and then buckled/kinked to force the mesh to curve. The panels are joined together with standard M20 bolts to form a completed arch to virtually any dimension and profile.

“The machine that makes the RamArch panels is a bit of a trade secret but it can be described as a large steel press,” said Hindle. “In fact we have two of them, the larger one puts the main crimps into the bespoke flat welded steel mesh panels supplied from a steel fabricator and the other smaller press the second crimps that cause it to bend to the required profile. The factory then fits the end connections that bolt the panels together and make the final on-site adjustments to the profile.

“The steel mesh bar sizes and spacings, together with the finished panel height, length, width, radius, connections and finish can all be made to a required specification for a particular tunnel, whether new or refurbished.”

A standard curved mesh panel is 2m long and 1.3m wide and the standard wire size is 8mm – although this can be increased to 15/16mm.

A complete arch of panels can be delivered stacked on one pallet and as each panel only weighs about 15kg, they are easy to handle. In large, high vaulted tunnels the arch can be assembled on the ground and then lifted into place by a telehandler.

“It’s idiot proof and builds itself,” said Hindle, adding that it can be made to any radius and is suitable for vertical shafts as well as tunnels.

The fully assembled RamArch provides a robust and stable continuous reinforced steel canopy to which shotcrete can then be applied.

“Penetration of shotcrete is pretty good because it’s such an open mesh system,” said Hindle. “It can also be used with steel fibres”.

The first use of RamArch was in Network Rail’s Whiteball Tunnel linking Somerset and Devon. The 1,094m-long tunnel was constructed between 1842-1844 by Isambard Kingdom Brunel and had significant areas of brickwork delamination and deep open joints. Considerable water ingress was affecting some areas and severely restricting the line’s speed.

Network Rail needed a rapid, safe method of temporary tunnel support that would enable a quick return to full line speed and that could later be incorporated into a permanent reinforced concrete internal tunnel lining.

The RamArch system was used to treat six areas, totalling 355 linear metres. The work was carried out successfully over six 48-hour weekend sessions.