A view of the Alte Burg site: A Rocket Boomer 353ES rig started drilling in the 874 m-long tunnel on March 15 - and reached the halfway point by May 6.

Atlas Copco equipment is working at three tunnelling sites on the road and one of them is the 7.9 km-long Rennsteig tunnel, which will be the longest road tunnel in the country.

The contract for this tunnel, valued at DEM 430 million, was awarded to Arge Rennsteigtunnel, a joint venture of Ed Züblin AG, Wayss & Freytag AG and Bickhart-Bau. The project got under way in August, 1998, and construction is expected to take 45 months.

Tunnelling is carried out using NATM (New Austrian Tunnelling Method), with top heading, bench and six attack points. Six Atlas Copco drill rigs - three Rocket Boomer 353ES and three Rocket Boomer 352 units - handle the drilling.

Main challenge

"The main challenge at this worksite is logistics," says Project Manager Karl Prax, who recently celebrated his completion of 50 km of tunnelling. "It is a bottleneck and makes our work much more demanding than the rock conditions in the excavation of this long tunnel."

Karl Prax, Project Manager at Rennsteig, recently celebrated 50 km of tunnelling. He says: "Logistics are our main challenge here."

Rock at the tunnel site is porphyr mixed with sandstone or quartz and has a compressive strength of 150-200 Mpa.

The Rocket Boomer 353ES rigs, equipped with the Bever Control system, are used to drill 120 holes (325 drillmetres per round) for blasting at the top heading. The rigs are equipped with Atlas Copco 48 mm button bits and R38 Enduro drill rods. Drilling is done with water flushing. After drilling the holes are blown clean with compressed air from GA 22 screw compressors, mounted on the rig.

High availability

Drilling time per round is 40 minutes, penetration rate is 4 m/min and drill bit life is described as "excellent."

The 25 drilling patterns installed in the Bever Control system make the Rocket Boomer 353 ES rigs well prepared for all drilling conditions. Advance per round is 2.5 m in rock classes 3 and 4.1, reducing to 1.7 m in classes 4.2 and 4.3. The other three Atlas Copco drill rigs - the Rocket Boomer 352 units - are used only for bolting and probe-hole drilling.

Germany's longest road tunnel: A Rocket Boomer 353ES drill rig is one of six Atlas Copco Boomer units driving the 7.9 kmlong Rennsteig road tunnel, which has twin tubes.

There are two Atlas Copco service containers at the worksite and the availability of the rigs is 98%.

If the laser-controlled profile of the tunnel is satisfactory, 3-5 cm of shotcrete is applied to the walls of the tunnel. Then steel arches are installed, with 1.7-2.5 m spacing, depending on the rock class. Steel mesh is then applied with another 10 cm layer of shotcrete, followed by the installation of 4-6 m rockbolts at the rate of seven bolts per metre of tunnel.

Karl Prax concludes: "The fact that we have six Boomer rigs working on this important project demonstrates the faith we have in Atlas Copco equipment.
Availability of the rigs, at 98 per cent, could hardly be better and the three rigs, which are equipped with computer supported drilling, are handling all drilling conditions with few problems."

Five rock classes

Both tubes at the 1,058 m long Hochwald twin-tube tunnel, which are 25 m apart, are being excavated simultaneously with the same equipment. It is being constructed by Arge Baulos Hochwald, consisting of Heilit+Woerner Bau AG and Jäger Baugesellschaft MBH.

The tunnel is being driven by top heading and bench with an advance rate of 4.7m/day for the top heading and 20 m/day for the bench. An Atlas Copco Rocket Boomer 353 Eagle with Bever Control is drilling 130 blastholes with 45 mm button bits and HEX35 drifter rods.

The rock is granite and has a compressive strength of 150-200 Mpa. Penetration rate is 3-4 m/min and to drill a round, including charging, takes less than two hours.

There are five different rock classes and the advance per round and required rock support is specified for each one. Swellex rock bolts are used in rock class 4 when there is a problem with water. Otherwise cement-grouted rebar bolts are used.

Walter Kubick, Site Manager at Hochwald, is pleased with the performance of the Atlas Copco equipment and his drill steel contract with the company.

Personnel at the site are pleased with the performance of the Atlas Copco equipment. Site Manager Walter Kubick, from Heilit-Woerner, says: "We have a drill steel contract with Atlas Copco which works well. We also have an excellent relationship with Hans Lauer, Atlas Copco's Technical Supervisor, who is a real superman. He is always on the spot when we want him, he knows exactly what he is doing and has never let us down."

Atlas Copco's Technical Service Manager, Hans Lauer, is described as "a superman" for his reliability, work and support at the Hochwald tunnel site.

Good performance

The Alte Burg tunnel is the shortest on the northern side of the mountains at 874 metres. It has twin tubes, each with a 7.5 m-wide roadway, and is being constructed by the joint venture Arge Tunnel Alte Burg, which comprises Schachtbau Nordhausen GmbH and Leonhard Weiss GmbH & Co.

An Atlas Copco Rocket Boomer 353ES equipped with COP 1838 rock drills is being used for the excavation of the top heading. Another Rocket Boomer 352 is employed in bolting and bench excavation and Atlas Copco Swellex 2.7 m-long bolts are providing rock support.

A Rocket Boomer 353 in the Alte Burg tunnel.

With the help of Atlas Copco 45 mm button bits, penetration rate is 4-5 m per minute and the drilling time for each 136-hole round is between 50 and 60 minutes.

May celebration

Site Manager Wolfgang Löbel says: "I've been using Atlas Copco tunnelling equipment since I started in the business with pneumatic equipment in 1970. Everyone on the site is very satisfied with the performance of the Rocket Boomer 353 ES rig.

"We started drilling on March 15, and we were holding our halfway celebration party by May 6. The availability of the rig has been 95%, and the only damage we have suffered was caused by a rockfall and a damaged cable.

Wolfgang Löbel, Site Manager at Alte Burg, has been using Atlas Copco equipment since 1970.

"We're also extremely happy with the performance of the Atlas Copco rock drills, which have a service interval of between 50-80,000 drill metres."

And Mr Löbel adds that the quality and performance of the drill bits is "excellent". The bits last some 700-1,500 metres without regrinding and the drill rods last up to 12,000 m.

The Rocket Boomer is equipped with a Bever Control to guide boom positioning and log drilling results. Before tunnelling was started, operators and maintenance crews had three weeks of training, closely followed by software training prior to delivery of the rigs.

Total cost of the Alte Burg tunnel is DEM 50 million and it will take an estimated 39 months to complete.