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A full circle view of tunnels

Internal view of tunnel

Tunnels can unlock congestion, create efficiency, make cities more functional and livable. Harry Asche and Anthony Bennett, two of Aurecon’s tunnelling experts, explore how we are delivering better solutions through smarter tunnels.

Road operators can now precisely manage traffic flows within tunnels. Systems can connect with built in vehicle technology to deliver improved traffic management solutions and safer driving. Existing tunnels can be retrofitted or widened, in some cases, while they continue to operate. Metro rail systems can respond to increased passenger demand and seamlessly schedule driverless train fleets to handle such variable, peak passenger periods. Constructing tunnels is safer and operating them is cleaner and greener. The future is now. 

Humans began constructing tunnels with picks, shovels and manual labour. Today, tunnelling is highly mechanised, using enormous Tunnel Boring Machines (TBMs) capable of operating 24 hours a day seven days a week. Constructing tunnels is increasingly automated and the equipment used is growing in size and technical sophistication. 

In the world of civil contracting and geotechnical engineering, the TBM is the equivalent of the modern commercial airliner. These mighty pieces of equipment are pushing the boundaries of what is possible and they continue to grow in diameter and capability. The largest TBM in the world measures a ‘whopping’ 19.25 metres in diameter. The machine was constructed to deliver the (now) mothballed Orlovski Tunnel project in St Petersburg. The largest TBM currently in operation measures 17.5 metres and is in operation in Seattle, Washington in the USA. While in Australasia, the 15.1 metre TBM excavating the Waterview Tunnel in Auckland, New Zealand holds the title for the biggest diameter machine.

With increases in the cutting diameter of TBMs, it is now possible to create a tunnel cavity that is capable of accommodating a double deck, three lane road design – something that would have been considered impossible 15 years ago. Is there a limit to TBM size? For the moment, it seems not.

Wider applicability and better automation

Talk to tunnelling experts and they will tell you that technology is playing an increasingly important role in the field. The heavy work is done using TBMs and there are two major categories of these machines – hard rock and soft ground machines. TBMs themselves consist primarily of a cutting head to pulverise material, a conveyor to remove the spoil and a system to move the machine forward to facilitate the actual tunnelling. 

“In the past, TBMs either dealt with the softest ground or the hardest rock but they are now capable of effectively dealing with mixed face conditions,” says Harry Asche, Unit Manager Transport Services at Aurecon. 

“In mixed face conditions, the skill is in knowing the material mix entering the machine and now operators have access to equipment that allows them to automatically measure spoil coming into the tunnel. This is done via belt weighers and scanners that employ automated, real time analysis.” 

“There is an increasing range of highly accurate measurement options for use on tunnelling projects. We can scan strata at the excavation face, employ highly accurate bubble detectors and manage machine performance via multiple, web-based data acquisition tools which can be reviewed on remote computers, tablet devices and even on smartphones,” adds Harry.

“Tunnel systems are entering a whole new era where smart technology is allowing us to deliver improvements in how we operate systems that use the infrastructure."

Smart systems - better performance

“While technology is aiding how we construct tunnels, the really exciting area is the way technology is allowing us to value-add to tunnel performance and management,” says Anthony Bennett, Techincal Director Transport Services at Aurecon. “The impact technology is having is delivering a genuine ‘step change’ in options to improve tunnel performance and by doing so, delivering infrastructure that better meets the needs of users and operators.”

Road systems

Tunnels with sophisticated management systems allow operators to offer benefits to users such as ‘safety based’ tolling or perhaps even to ultimately discourage ‘old technology’ vehicles from the traffic mix. For example, modern, hybrid technology equipped vehicles may attract significantly lower tolls than old fashioned, high emission vehicles. The benefits of number plate recognition and vehicle scanning are driving improved system performance and include: 
  • Preventing over-height vehicles entering tunnels and to fine drivers if they do so
  • Identifying and fining drivers that enter tunnels when carrying hazardous goods or trailers that carry such goods
  • Encouraging the use of hybrid or electrics by differential tolling – this may result in ‘managing out’ vehicles with high emissions due to higher tolls being imposed on such drivers
  • Financially rewarding drivers of vehicles with desirable features such as a low fire load, low emissions hands-off technology, etc. 
  • Managing traffic flow via hands off technology, which will allow more capacity because the gap between cars can be reduced 
In New South Wales, Australia truck operators whose vehicles emit heavy exhaust smoke are being fined when they use tunnels. This technology has virtually eliminated such vehicles from tunnels and improved internal air quality dramatically. As a result of these and other technology-based solutions, user safety and vehicle flow is greatly increased as the variability of human error, accidents, emissions and vehicle hazards are significantly reduced.

Rail and metros

With congestion a critical issue for rapidly urbanising societies, metro systems offer a rapid movement and highly effective ‘below ground solution’ to address mass rapid transit needs. System performance is critical for user satisfaction, so operators are looking at ways to introduce passenger sensing systems and match passenger numbers to train services. Technology in metros is now delivering:
  • Driverless trains which allow for reduced operation costs and flexible timetabling, ultimately delivering timetable-free metro systems
  • Trains with minimised fire loads, as operational safety is improved 
By using driverless trains, it is possible to rapidly scale (up or down) rolling stock capacity to meet passenger numbers. As operators do not have a fixed cost of labour (drivers), system performance can be enhanced without the need to schedule drivers that may not be required. 

This flexibility offers improved system performance for passengers and cost benefits for owner/operators. In addition, the design specifications around such factors as fire load within the metro system can be modified, resulting in a reduction in the overall cost of design and construction of the asset and the rolling stock. Critically, the system is scalable in that it copes seamlessly with the steady growth in passenger numbers, typical of urbanised societies.

Enhancing existing tunnels

In mature markets, such as Europe, approximately 50 per cent of work undertaken on tunnels is actually refurbishment of existing systems. In the past, reconfiguring a tunnel’s capacity (e.g. changing from two to three lanes or increasing the tunnel diameter) was impossible. In Europe, there are examples of tunnels being widened using a technique that incorporates a box-like structure constructed outside of the existing tunnel lining, in which the construction engineering is undertaken, while the tunnel remains in either full or part-time use. 

In some instances, tunnel boring machines have been used to undertake parallel excavation works. The capability to increase capacity has been utilised across tunnel infrastructure servicing roads, rail and utilities. The flexibility to widen tunnels results in a once fixed capacity asset being able to be reengineered to meet increased capacity requirements. This capability allows engineers to take advantage of the embodied energy in the existing structure to create a better system that uses less energy to operate, in contrast to constructing an entirely new system.

At a smaller scale, a conventional steel box constructed around an existing tunnel allows widening of tunnels to be undertaken using machines known as ‘Pipe Eaters.’ These machines are capable of excavating around existing tunnels such as sewers, while allowing water flow to continue as the sewer diameter is increased. 

“Tunnel systems are entering a whole new era where smart technology is allowing us to deliver improvements in how we operate systems that use the infrastructure,” says Harry. “Within a generation, we will see a huge change in the way we use road, rail and utilities delivered via tunnels.”

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