The Brenner Base Tunnel is one of Europe’s most comprehensive and important infrastructure projects in modern time. LKAB Wassara’s W120 water-powered hammer played a decisive role in the making of the tunnels going under the river Isarco, near Fortezza in Italy.
The Brenner Base Tunnel (BBT) is the main segment of a new railway line that will connect Munich with Verona. BBT runs between Innsbruck and Fortezza. The new tunnel will lead to an improvement for, above all, the truck traffic through the so-called Brenner Pass. The two-tube tunnel system will be 55 km long, making it the longest underground railway stretch in the world
Stabilization of the ground
The excavation of the tunnel started from 4 shafts on the riverbanks, two on each side (see the main picture above). Before the excavation of the shafts could start ground improvement by jet-grouting was needed. The jet-grouting was to be performed both to stabilize and to seal of the water in the shaft, as well as improving the ground from the surface before excavating the tunnels.
Columns were made with the Wassara W120 hammer
The columns were made up to 40m in one single pass. LKAB Wassara’s W120 water-powered hammer with a Ø152mm drill bit was used for this. Above the W120 hammer a monitor was mounted. The monitor worked both as a nozzle holder for the Jet-grouting and a flow diverter that diverts water from the water channel in the drill pipe to the hammer. The monitor is of a double flow type where compressed air is used to improve the performance of the jet-grouting. The water, air, and jet grout are supplied through a 127 mm triple wall drill tube securing that the fluids are not mixed.
PREFERRED SOLUTION - Water-powered drilling
Rotary-Drilling - Rotary drilling is normally used when jet-grouting, but was discarded due to the complicated soil conditions with frequent boulders and large blocks. Water-Power drilling solved the problem of drilling through the block and boulders.
Air DTH technology - In a comparing test in the beginning of the project, Wassara’s water-powered hammer outperformed a pneumatic DTH hammer, drilling more than double as fast as the pneumatic hammer.
A 36-meter deep hole was drilled with the two different techniques. The Wassara hammer drilled the 36 meters in 40 minutes and the pneumatic DTH hammer used 1 ½ hour for the same depth. Each rig could now produce 7-8 columns per day during 24-hour operation. The low performance of the air hammer was most likely caused by the high water-table.
“The Wassara DTH technology outperformed other alternative methods.”
Magnus Hörman, Senior Engineer, LKAB Wassara.
Left: W120 Hammer and monitor, Middle: Monitor and triple fluid rods, Right: Solimec SM 28 in action
Special thanks to:
Antonio Celot /Project Manager at Webuild and Valerio Salvi, Research & Development, CRM