Tunnelling: Underground innovations

Tunnelling is such a specialised area that new machines do not come around all that often. However, last month’s Bauma exhibition was a catalyst for some interesting launches.

Atlas Copco, for example, used the show to take the wraps off a new high speed rock drill for tunnelling and similar applications in the 43 – 64 mm diameter hole range. The company says the COP 4038 drills +20% to +30% faster than anything else on the market thanks to the company’s expertise in high frequency drilling, and is designed for hard rock applications. The unit boasts an impressive 40 kW of power and comes with a double damping system to absorb reflex shock waves, making it possible to drill fast without increasing wear on the rod.

As far as its underground drilling rigs are concerned, the company has developed a new version of its Rig Control System. All functions have been grouped in nine blocks under a new tree structure for easy navigation and are access with a new touch screen display. Atlas Copco says this not only makes using its drill rigs easier, but also cuts down on training time for new operators.

Also new is the company’s Underground planning, evaluation and documentation software, which is available on all Atlas Copco underground machines. The system contains a new drill plan generator, complete 3D view of the tunnel, smart interpolation of contours, and an improved log and report function.

In terms of the drill rigs themselves, Atlas Copco is now offering a totally water-free drilling system on its Boomer XE3 C rig. The system uses compressed air alone to flush cuttings from the hole, while a suction hose captures dust and transports it to a sealed container for disposal. The system has obvious advantages for projects where water is scarce or in situations where either the rock conditions or ambient temperature would make it difficult to use.

The technology on Sandvik’s tunnel drilling rigs, meanwhile is packaged into a system called DTi, which was first introduced in 2008. Features added since include wireless local area network (WLAN) remote access and the iBolt navigation and bolting system. The very latest additions are an Access Detection System that stops feed and rotation if a person enters working area near the booms, while the rigs themselves are also available with Sandvik’s new high frequency RD5 series rock drills.

The Access Detection System is an important safety enhancement built around sensors on the sides of the jumbo. If they detect in the dangerous area near the booms, rotation and feed will automatically stop. This prevents anyone from entering the working area while the booms are in operation and a separate reset is required by before drilling can re-start.

The new RD5 high frequency rock drills, meanwhile, feature a low profile design and a patented stabiliser with an intelligent control system that dampens harmful shockwaves. The simple body structure of the drills along with their modular construction and visual wear indicators are designed for ease of use and maintenance.

Sandvik says these units offer +15% to +20% higher penetration rates and significantly longer tool life compared than the previous HLX5 range.

Metro focus

Talking about tunnelling projects often brings to mind large schemes to build inter-city, or even international transport links. But in many fast-growing developing world cities some of the most interesting and challenging projects are light rail schemes to help alleviate congestion in the face of an urban population explosion.

In Wuxi, China for example, Herrenknecht has supplied a total of eight tunnel boring machines (TBMs) which have been used to excavate some 16 km of tunnels in just 20 months to build the first two of a planned five-line metro system.

The earth pressure balance (EPB) machines measure just under 6.4 m in diameter and have been at work since July 2011 up until the final breakthrough in March this year.

The record advance rates were 33 m a day and 164 m a week, and this was achieved in difficult conditions with little cover, close to residential and commercial buildings in the 4 million-strong city.

Close conditions

Indeed, the construction of tunnel S-663 involved boring to within 7 m of the surface and 3.7 m of existing foundations. To avoid damage in the clay soil, a freezing procedure was used to stabilise the ground.
At least five metro lines are planned for Wuxi in the future. The newly built Lines 1 and 2 have a total length of 58.5 km and are expected to start operation by the end of 2014. Line 1 will cross the city from north to south, and Line 2 from east to west. Herrenknecht received orders for five EPB Shields for the construction of Line 1, and orders for three machines were placed for the construction of Line 2 from contractors including Shanghai Mechanised Construction, Shanghai Baoye Construction, China Railway, Wuxi Hong Yuan Construction and China Railway Tunnel Group.

Moscow, Russia also has an ambitious metro construction plan in place, but unlike Wuxi, the emphasis is on increasing the capacity of the city’s light rail network, rather than starting from scratch. The city’s government has launched a scheme to build 50 km of new lines by 2016, almost all of which will be underground.

Current work is aimed at preparing the sites where the future stations and lines will be built. This task is a challenge due to the density of Moscow – it is not easy to find appropriate sites that can host train depots, stations, ventilation chambers, emergency exits, and other facilities for the metro. In those areas that have already been designated for metro construction, many utility and communication lines must be relocated. As Moscow’s deputy mayor for urban development and construction, Marat Khusnullin, said, “Unfortunately, there is a complication related to the lack of existing construction projects, and therefore the first thing we had to do was to invest in planning and design activities.”

The programme will bring the Moscow metro system to 451 km, with 252 stations at a cost of some RUR 100 billion (US$ 3.2 billion) per year over the construction period. “This country has never built a metro system on this scale, even in the best Soviet years,” said Mr Khusnullin.

Tunnelling is already underway at several sites, and Robbins has supplied three new EPB TBMs. Fitted with electric variable frequency drives (VFDs), Robbins says they offer high thrust and torque capabilities to allow faster excavation and minimal disturbance.

Active articulation on the machines will enable them to excavate tighter curves without the risk of segment deformation that is present when using passive articulation. Mixed ground cutterheads reinforced with abrasion-resistant wear plate give the option of changing out carbide knife-edge bits with 17 in (432 mm) disc cutters depending on the conditions. Two 6.6 m diameter Robbins EPBs are excavating left and right-hand tunnels, each 1.8 km in length, for contractor Engeocom. A third, refurbished machine for Engeocom, nicknamed “Julia”, is also excavating a 2 km section of tunnel. The final machine, a 6.2 m diameter Robbins EPB with mixed ground cutterhead, is boring a 1.9 km section of tunnel for contractor USK MOST.

All four machines are using Robbins continuous conveyors.The USK MOST TBM is scheduled to breakthrough later in spring 2013. It will be disassembled in the receiving station site and launched on an additional 1.4 km tunnel in the first quarter of 2014. Additional work for USK MOST includes 8 km of tunnel and seven stations using multiple TBMs including two Lovat and two Herrenknecht EPBs.

Record breaker

But this popularity for metro schemes does not mean the big projects aren’t out there too. On March 22, for example, breakthrough was achieved on Asia’s longest tunnel, the
44.6 km Pahang Selangor Raw Water Tunnel, which will provide to the capital Kuala Lumpur.

Once completed, the tunnel will transfer 27.6 m3 of water per second to a new treatment plant. The drinking water will supply about 7.2 million people for project owner KeTTHA (Malaysian Ministry of Energy, Green Technology, and Water).

The tunnel was driven with 5.23 m diameter Robbins Main Beam TBMs with continuous conveyor systems. Despite blocky rock, over-break, power cuts and water inflows the contractor joint venture of Shimizu, Nishimatsu, UEM Builders, and IJM Construction (SNUI) achieved a maximum advance rate of more than 650 m per month.

In Europe meanwhile, January saw the launch of a 9.93 m diameter Aker Wirth telescopic shield TBM for the construction of lot 2 of the 32.9 km Korlam tunnel in Austria. It is digging the south tube of the main 18 km section as part of a new high-speed rail link between Graz and Klagenfurt.

Access to the underground construction work areas was a particular challenge for this project. The main components of the machine were transported to the assembly cavern in the mine via a 60 m deep shaft and subsequently reassembled there by Aker Wirth and the ARGE KAT2 contracting consortium, comprising Strabag AG and Jäger Bau.