Speeding to success in Gothenburg rail tunnel

The new tunneling drill rig Boomer XE4 C, is proving to be a winner in the expansion and upgrade of the Swedish rail system near Gothenburg. This fast and highly efficient rig drills pre-grouting holes as well as blast holes and has an automatic rod handling system, all of which is helping to keep the work on track to meet the 2012 completion date.

Inside the Kattleberg mountain: The fully computerized Atlas Copco Boomer XE4 C drill rig drills blast holes as well as pre-grouting holes in what will be the new rail tunnel. The Hede–Älvängen railway tunnel near Gothenburg, Sweden, is rapidly on its way to completion. The project got under way in February 2010 and by January this year, more than two thirds of the 1.8 km tunnel had been excavated.

The new, twin-track railway is part of a major upgrade of the Gothenburg to Trollhättan line – a stretch of about 70 km – paving the way for high speed trains and doubling the capacity of the existing network in the south west of the country.

The tunnel, which is being driven through the Kattleberg mountain, is 13.5 m wide, 10.8 m high and includes the construction of an emergency escape tunnel (cross section 35 m2) as well as a 500 m long adit. “Everything has been going smoothly on this job so far and we are achieving all of the targets we set out to achieve,” says Anders Östberg, Plant and Machine Manager for the contractor, Veidekke Entreprenad.

Östberg attributes this to the skill of the Veidekke engineers coupled with the advanced capabilities of the drilling equipment being used – an Atlas Copco Boomer XE4 C, a new, fully computerized, fourboom drill rig that drills holes for pre-grouting as well as blast holes. Automatic rod handling is making a significant contribution to speed and efficiency.

Joint development project

Sweden is one of the few countries in the world where pre-grouted, unlined tunnels are consistently used for civil tunnel works and the Hede–Älvängen rail tunnel is no exception. When the contract was won by Veidekke, a sub-contractor to the Swedish construction company PEAB, the company decided it would need a four-boom drill rig that could drill all of the required pre-grouting holes as well as the blast holes – and preferably without increasing the number of operators.

The company worked with Atlas Copco on the design and, after several months, unveiled the Boomer XE4 C. The rig features four booms, each equipped with high frequency COP 3038 rock drills, the automatic rod handling system (Auto RHS E) for drilling up to 30 m long grout holes, and the Atlas Copco Rig Control System (RCS) enabling all of the functions to be handled by just one operator.

The rig was delivered in mid-2010 and today, with some 70 000 m of grout holes and 300 000 m of blast holes to its credit, it is clearly proving its worth in terms of production as well as increased safety.

Focus on operator safety

Like most European construction companies, Veidekke normally uses one operator for its three-boom rigs. With the new Boomer XE4 C, not only has the number of booms been increased from three to four – increasing productivity – but still only one operator is required, reducing the risk of communication errors between different operators.

Safety is further enhanced thanks to the rod handling system which eliminates the need to stand on a platform, manually coupling and uncoupling threaded joints in order to extend drill rods.

Östberg says: “The Boomer XE4 C is doing great and we are especially pleased with the automatic rod handling system which has made a great contribution to efficiency and safety.”

Each rod carousel holds up to eight, 3 m rods. This is particularly appreciated when drilling grout holes which are all more than 20 m long. Comments Site Manager Peter Ahlgren: “Instead of spending time on adding rods, this allows our operators to concentrate totally on drilling.”

He continues: “When you can drill four holes at the same time, the rate of advance is extremely fast. With the Boomer XE4 C, we are able to advance the face about 25 meters per week, including pre-grouting of all the tunnel meters. With each blast, we advance six meters and that means we don’t have to drive the rig in and out of the tunnel so often.”

Precision is also important and it is vital that the tunnelers achieve the roof height of precisely 10.8 m. Once the high speed trains start running, a powerful vacuum will be created in the tunnel and there has to be enough room above the trains, as well as at the sides, to release the pressure.

To the operator, Niklas Karlsson, who has more than 25 years of tunneling experience, the Boomer XE4 C is the ideal solution. “I’ve been in this business a long time and I have tested most of the drill rigs that are out there,” he says. “I can quickly tell if a particular rig is going to be suitable for a specific tunnel or not and I think this one is perfect for the work we are doing here, especially when it comes to pre-grouting. I like having rod handling carousels on all four booms, and the rig drills fast and straight holes, just as they should be.”

For navigating and positioning, the operator can use Total Station Navigation, an automated system that increases precision drilling and eliminates the need for surveyors. Meanwhile, Veidekke is also simultaneously driving the emergency/service tunnel using the smaller rig, the two-boom Atlas Copco Boomer E2 C.

The entire railway upgrade, which also involves a number of new bridges and stations along the Gothenburg to Trollhättan line, will cost approximately EUR 1.5 billion. The new rail tunnels are expected to be completed by mid-2011 with the first high speed trains running from December 2012, gradually building up to an average of about 120 trains per day.