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OF THE ALPS The extension of the Trans-European highway system has brought Austria into focus as a major crossroads for European traffic. As part of the effort to upgrade infrastructure, two major tunnels are being excavated with Atlas Copco drillrigs and self drilling rockbolts at the forefront.
Whether travelling between the Balkan States and northern Europe, or between eastern and southern Europe, the risk for traffic congestion is such that Austria currently bans trucks from its highways during the night hours. In its efforts to upgrade to full European standards, Austria is building more dual carriageways and driving parallel tunnels for a number of existing bi-directional tunnels across the country. There, the latest in Atlas Copco technology is being put to use, including Rocket Boomer rigs and self drilling rockbolts. Mining & Construction has visited two such projects: a new parallel tunnel to go beside an existing one located in Graebern on the Vienna-Klagenfurt section of the important A2 motorway which connects Vienna with Italy, and a new twin-tube tunnel project at Steinhaus, located near Semmering.
Twin tunnels at Graebern A new 2,148 km-long tunnel is being driven parallel to the Graebern tunnel. It is being driven from both ends in highly variable ground conditions, which requires flexible approaches to excavation and support. The contractor is a joint venture of Ostu Stettin, Hinteregger and Porr Tunnelbau. In part they are using equipment, such as the Atlas Copco drillrigs, that was released following the excavation of the 9.9 km-long Plabutsch tunnel at Graz - a similar project recently completed on the A9 motorway. Some 1.5 km of the tunnel is being excavated to standard 70 sq m section, 400 m of which is in excavation class 7 (see table on page 7) and will have a reinforced shotcrete or concrete invert requiring an enlarged section of 78 sq m. An oversize safety section will be excavated in the centre of the alignment to provide a third lane over a distance of 48 m, where vehicles may park in an emergency, possibly turn around, or turn to enter a wide cross passage leading to the second tube. The latter will be dimensioned to facilitate the movement of trucks.  The Rocket Boomer L2 C at work at the south end of the Graebern tunnel. Reinforcing the rock At the south end, where the rock is generally too soft for blasting, an Atlas Copco two-boom Rocket Boomer L2 C is drilling for spiling and bolting in the top heading, so that the face can be mechanically excavated. The area is intensively folded and faulted, with a mixture of competent and incompetent rock. As there was no glacial cover during the last million years, the highly tectonised and incompetent parts present at the southern portal have not been removed. The centre section of the top heading - up to 5 m in length - is generally left in place as a safety pillar, to support the tunnel face. Part of the excavated face is also temporarily secured by 12 m-long self drilling anchors, which are grouted in place, and an application of reinforced shotcrete. Sectional lattice arches are erected at 1.0 - 1.2 m centres. For systematic bolting, self drilling rockbolts or cement-grouted anchors with lengths of 4 m or 6 m are used. When required, 4 m-long spiles of pipes with a diameter of 25 mm are set around the roof profile in 45 mm-diameter holes drilled by the Rocket Boomer L2 C. Any blastholes required are drilled using 45 mm Atlas Copco Secoroc bits. The top heading is followed by a 2.7 m-high bench and invert, which are excavated 60-80 m back from the face, but can periodically slip back to 150 m behind the face. At the north end of Graebern, the rock is biotite gneiss, a more competent metamorphic sediment with a high amount of quartz and feldspar. Predominantly, the rock mass is jointed and faulted and so, mostly decomposed and friable. Therefore spiling with pipes is often an absolute necessity. In addition, Super Swellex 4 m-long bolts are set in the roof as immediate support. Regular support comprises 15 cm of shotcrete with one layer of wire mesh and 4 m-long rockbolts. If spiling is required, lattice arches are erected, and shotcreted in place. A three-boom semi-automatic Rocket Boomer L3 C performs the support drilling duties at the north end, in addition to blasthole drilling. Drilling of a full round of approximately 130 x 2 m-deep holes in the top heading takes an hour, in addition to a half-hour for charging and blasting. Blasting agents are dynamite and cartridged slurry, with 19 intervals of electronic detonators with millisecond delays at 80 milliseconds per step. The rounds are set up using an array of seven lasers. The Rocket Boomer L3 C is equipped with ABC Regular advanced boom control, and has dual operator panels. Ostu Stettin now have two years experience using this machine, and are impressed by the accuracy of its profile drilling. "The absolute control over hole depth produces consistent blasting results, and provides a clean face using the minimum amount of explosives," says Graebern Site Manager Manfred Sachs. "In these severe geological conditions, there is less damage to the strata forming the tunnel profile, and less overbreak, resulting in lower consumption of shotcrete. "The elevating cabin affords a good view of all face operations, which is particularly important when blasthole drilling, spiling and rockbolting are carried out simultaneously."  Pipe spiles are used to support the roof until shotcrete and steel arches can be installed (right). Rocket Boomer L3 C at the Graebern north top heading (left). Steinhaus at Semmering The Steinhaus tunnel is on the B306 Vienna to Bruck road, which passes through Semmering, a favourite skiing resort for the Viennese. The B306 is being expanded with a new tunnel, and will form part of the new S6 highway. This will connect with the St.-Michael interchange on the section of the A9 Trans-European Highway between the main centres of Graz and Linz. The tunnel being driven is twin-tube and 1.5 km-long, on a double curving alignment that takes it into the side of the valley in which the village of Steinhaus is located. It is under construction by Bilfinger Berger for the Austrian highways authority. The rock quality is variable, generally soft and non-glaciated, comprising chalk, phyllite, calcite and quartzite with a maximum cover of 60 m. The tunnels will accommodate a two-lane highway in each direction. There will be three cross-passages, with the middle one having a large cross-section to facilitate the switching of trucks between tubes in emergency. The full 80 sq m section of each main drive is achieved with top heading, bench and invert excavations. The faces will pass beneath some village houses with around 50 m cover, and two blast vibration monitoring stations have been set up. Work at Steinhaus commenced at the west portal with a 47 m-long central pilot tunnel, within which the pillar between the two main tubes was cast using self-compacting concrete. The separation over the first 50 m of alignment was 2 to 4 m, increasing progressively to 60 m at the halfway mark. The rock pillar on the second 50 m of drive was anchored using pre-stressed bolts, tightened by plates on both sides.  Click to view larger image 10-20 blastholes required The drillrig fleet comprises three late-series Atlas Copco Rocket Boomer 352s, and one newer Rocket Boomer L2 C. They spend 80 percent of their time drilling for rock reinforcement because, generally speaking, only 10-20 blastholes are required in the faces of the top headings. The faces, which are mechanically excavated, are secured by up to nine 16 ft-long self drilling rockbolts with mortar injection. Roof and wall support is achieved mainly with grouted rebars and self drilling rockbolts and five MAI M400 water mixing pumps are used for grouting. In order to maintain reasonable underfoot conditions, a temporary shotcrete invert reinforced with steel mesh is laid in the top headings, every 4 or 5 arches on advance. Drainage holes are drilled in the face whenever necessary. Usually 3-4 arches will be set at 1.5 m intervals in each face during a 24-hour cycle of three shifts. At the 90 m mark on the south drive, a 20 m-high karst cavity was encountered, which, fortunately for the tunnellers, proved to be dry. The drill rig stood away, drilling over the face and into the cavity. Some 30 cu m of 8 mm concrete was then pumped through the drillholes, using one of the shotcrete jumbos. Advance beneath the filled cavity was protected by arches of 20-30 spiles made of 51 mm x 8 m-long R32 pipe installed at 2 m increments for a 10 m stretch. Once into more competent ground, the drill rigs were able to deliver 80-90 holes/round in the top headings, drilled to depths of 1.5-1.7 m. Blasting is initiated by millisecond and long delay non-electric detonators, using encapsulated slurry as the main blasting agent. The bench follows at between 90 m and 220 m behind the face, where the temporary invert is ripped out by an excavator with hydraulic hammer.
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