Efficient Connection from Munich to Garmisch-Partenkirchen: The new Oberau Tunnel
In December 2017, the breakthrough was realized at Oberau Tunnel near Garmisch-Partenkirchen in Germany. The 2.8 [km] long tunnel forms part of the 4.2 [km] long, four lane bypass for Oberau, which will eliminate a bottleneck on the B2 federal road, one of the central north-south routes through Bavaria.
80% of the double tube tunnel was advanced using the blasting method in hard rock – dolomite and limestone. 20% of the advancement was carried out using excavator driving in the unconsolidated rock of the Giessenbach Valley Crossing. The excavated cross section was temporarily stabilized in accordance with the New Austrian Tunneling Method (NATM) using anchors, spiles, steel arches, mesh and shotcrete.
In the first section, the top heading was excavated, followed by the bench and the invert. The middle advancement rate was approx. 10 [m] per day in hard rock and up to 2 [m] in unconsolidated rock.
Advancement was especially challenging in the unconsolidated rock section that was prone to settlement in the Giessenbach Valley: In this section, buildings had to be crossed below at a cover of less than 10 [m]. For compensating the expected settlements at the surface, advancement accompanying elevation grouting was carried out in the area where advancement was carried out below buildings.
Advancement was carried out by conventional NATM calotte driving with 6 [m] long AT – TUBESPILETM Spiles that were used as pre-support.
AT – TUBESPILETM Tube Spiles are ideal as pre-support in conventional tunneling. The application of the tube spiles permits the stabilization of local instabilities in the excavation area and prevents ground loosening induced by installation.
The AT – TUBESPILETM is installed in one step through rotary percussive drilling using conventional drill booms. The drill rod inside the spile tube transfers the drilling energy onto the drill bit, which is available as a button drill bit with carbide inserts and as a hardened arc-shaped drill bit. The tube spile is pushed into the borehole by an adapter and follows directly behind the drill bit.
The two tunnel tubes were successfully advanced underneath the Giessenbach Valley using this method.