Construction of a large cave – the BLS wants to the lötschberg tunnel, flick several times to the new lötschberg tunnel was closed due to water ingression. A cavern in the Tunnel to prevent this in the future.Cyrill Pinto3 Kommentare3Dreimal was flooded, the tunnel tube, the clean-up costs are estimated at 10 million Swiss francs.Video: Tamedia

the Week were experts, as was the repeated water ingress in the Lötschberg base tunnel. The leaders of the BLS presented today in an online presentation of their findings: in fact, the damage to a water pipeline was built, the karst water from the mountain into the tunnel interior and, thereafter, a distribution Cabinet by means of a pressure line to the South portal to the outside leads.

The System for years, works well, – said the Director of the project Alptransit BLS, Stefan Irngartinger before the media. Then was gone in February, suddenly more water over the exploratory drilling R37 into the System. The accumulated water creates such a high pressure that the pipe and the seal to a crack. As the water rushed into the tunnel interior and muddy the railway line with a length of about 500 meters, 30 centimeters high.

Although experts criticize the procedure, water from the mountain to dissipate in the Tunnel, the BLS about it. It makes sense to keep up with this dissipation system, the water pressure on the Tunnel as low as possible, said engineer Irngartinger. The Alternative would be to have the building completely sealed, and to build much more massive – with the residual risk that the Tunnel would not, in spite of the significantly thicker tunnel shell to the pressure. “In the current variant with the discharge of the water, the risks are significantly lower,” said Irngartinger.

a variant of the “cavern”

In recent weeks, the BLS engineers have already developed several variants for the refurbishment of the tunnel. In late summer you want to submit to the Federal office for transport (BAV), a project for planning approval in the autumn with the construction work to begin. By the team of experts at the BLS, the variant is set to “cavern”.

for A 1000 cubic meters large cave in the Rock to the water from the borehole 37 of the field. “So that we can create the necessary volume to large water and sludge volumes to absorb,” says Irngartinger. For the construction of the tunnel has broken casing on a length of 10 to 15 meters and the vault be opened to the cavern to escape. After its completion, it is intended to cover large water volumes and prevent that water can penetrate into the tunnel tube.

the mud out of the cavern you want to blades by means of a simple System from the cavern, and with wagons, in addition to transport. “We are convinced that it is impossible to seal the borehole to prevent large water pressure on the tunnel,” said Irngartinger.

the cost of repair is between a high single-digit to a low double-digit million amount. These costs would be covered through the ongoing performance agreement with the Federal government. During the construction of the Eastern tube remains blocked, the West tunnel, but can remain open to trains, so, in spite of the construction of the base tunnel. However, it is possible that the Tunnel had to be blocked on each of the days, at night completely.

Between the exploration drilling and the acquisition lines, The BLS graph shows where the water line held the pressure.Graphics: BLSErdbeben as a trigger?

But why did the large quantities of water in the karst system via the Tunnel, only 13 years after its commissioning? When asked about this, mentioned Irngartinger, several small earthquakes, which were occurred before the first water inlet in February. These could penetrate the water-bearing cave system, the the Rock, such as tree roots, and so have changed, that more mud, Sand, and water penetrated in the drill hole above the Tunnel. With safety you could not say the but.

Karst is unpredictable, said Irngartinger. You just try to keep the risk as low as possible. In addition to the approximately 500-Meter wide karst zone in the South, there is another at the North portal in Frutigen. There had occurred during the driving of the tunnel, but less water. Therefore, we considered this second karst zone in the North as less of a problem.

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