Ground preparation at Semmering Base Tunnel
07 Feb 2013
Minova News Release
In 2015 excavation of one of Austria's most ambitious tunnel projects - the 27.3km New Semmering Base Tunnel - will begin. Ahead of that and since April 2012 vital preparatory above-ground work, including clearance and excavation of the entrance ramp site, has been proceeding at pace.
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Ramp stabilisation with shotcrete and Minova anchors
- In April 2012, work started on one of the most ambitious construction projects ever carried out by Austrian national rail company ÖBB-Infrastruktur AG. Scheduled for completion in 2024, the €3.1 billion New Semmering Base Tunnel will run 27.3km through the Semmering range to cut journey times on the south railway connecting Lower Austria and Styria.
- Before construction can begin at the entrance portal and on the tunnel bores, work concentrates on the above-ground sections with the clearance and excavation of the entrance ramp.
- The slope is currently being excavated by contractor Baubeteiligungsgesellschaft BBG-GRAZ. The new face is supported with shotcrete and ground anchors. The anchors selected by BBG are the permanent self-drilling anchors produced by Minova MAI, which provide an economical bolting solution for softer rock formations.
- "We have worked with Minova a number of times, and we are satisfied with the advice and the flexibility that Minova has given us," said Franz Schweighofer, Managing Director of BBG-Graz.
- Excavation of the precut proceeds using the the so-called pilgrim steps process in which benches of 6m-10m long and 2m high are supported in between with blocks of soil of similar dimensions. The cuts are secured with shotcrete and self-drilling anchors before moving to the next sequence.
- The CE-certified permanent self-drilling anchors by Minova MAI are an effective means for such bolting in soft or sandy rock formations.
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Ramp excavation is in 500m x 60m-80m x 10m steps
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About 1,600 Minova anchors stabilses the slope
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Anchoring for stability
For more efficient anchoring, BBG-GRAZ relies on a semi-mechanised setting process that uses an integrated rotary injection adaptor (IRIA). In this method, the hollow rod is installed with a sacrificial drill bit. Depending on the ground conditions a cementitious grout or resin is pneumatically injected into the rod during drilling. Once the planned depth has been reached, a specialised anchoring grout is fed through the rod, which hardens to a concrete strength sufficient to bear the intended loads. A selection of drill bits is available to match the geological properties at the site. The varied geology of the Gloggnitz application requires the full range of Minova MAI drill bits. - With a precut of about 500m in length, and a cut height of approximately 10m, the site will use some 1,600 permanent self-drilling anchors at lengths of 8m-12m and in a patterns of 1.5m x 1.5m. Shotcrete provides the final cover of the new 5,000m2 slope.
- When the surface works are complete, excavation of the twin-bore, single-track main tunnel, using conventional and continuous excavation methods, can begin.
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Base line tunneling to begin in 2015
The New Semmering Base Tunnel route supercedes an earlier alignment that ran along the opposite side of the existing railway pass. The pilot tunnel of that earlier project is the subject of the 1996 reference article. Rather than the single-tube double-track design of the earlier project, the new project comprises twin tunnels of 10m diameter, about 40m-70m apart, and connected by cross-passages every 500m. The geological challenges of the chosen route requires two tunnelling methods - NATM drill+blast and TBM excavation.
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Scenic Semmering rail route limits speeds to 50km/hr
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Alignment of the 27.3km New Semmering Base Tunnel
- The current schedule envisages tunnel excavation to be finished by 2020. Passenger and freight trains are expected to begin using the tunnel, at speeds of up to 230km/hr, at the end of 2024.
- Once completed, the New Semmering Base Tunnel will be one of the longest rail tunnels in Austria. It will act as a vital link on the route crossing Europe's heartland from Northern Germany to Italy. The current railway climbs the steep Semmering Pass between Gloggnitz and Mürzzuschlag on a historic mountain railway that is recognised as a UNESCO World Heritage site.
- The old route imposes considerable limitations on heavy freight transport, and passenger trains slow to a speed of about 50km/hr. The New Semmering Base Tunnel will bypass this bottleneck and cut 30 minutes off the journey between Vienna and Graz. It also represents a particular advantage for freight traffic. The new route's minimal incline of 0.84% removes all obstacles even for heavy freight trains. Currently the gradient is 2.5% for more than 60% of the 41km long mountain pass, with curves of 190m radius at numerous locations.
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Semmering pilot tunnel drive - TunnelTalk, February 1996
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