Sealing measures at Sedrun almost complete
Feb 14, 2007
In the southward drive of the Sedrun section, injection work has been in progress since the end of October 2006. These sealing measures are to prevent further water from being drawn out of the rock. By Christmas, the water ingress was reduced by half to 5 litres per second. By mid-February 2007, the injection campaign should be complete. Driving to the south will then be resumed.
Challenging tunnel construction
Whenever a tunnel is driven, water seepage from ground level must always be expected. Even in deeply lying drives such as the Gotthard Base Tunnel, water ingresses are unavoidable. This drainage of water causes fissures in the rock to close to a certain extent, which can lead to deformations on the surface. Such phenomena were detected in Switzerland during construction of the exploratory drive for the Rawil tunnel near the Zeuzier reservoir, and in the area affected by the Gotthard road tunnel.
The overriding goal of AlpTransit Gotthard Ltd is therefore to secure the tunnel drive in such a way that the reservoirs lying above it are not damaged. So that this goal can be accomplished, AlpTransit Gotthard Ltd has initiated various measures: Advance explorations and injections at the tunnel drive as well as a unique automatic monitoring system for the Curnera, Nalps and Santa Maria reservoirs.
Monitoring system has proved itself
Experience to date in the Sedrun drive to the south shows that construction of the tunnel has caused deformations in the range of millimetres in the surface terrain. In view of the limited settlement, no damage has been detected so far.
More surprising to technical specialists is the fact that the observed deformations have already occurred with very limited volumes of water. The ingresses to the Gotthard Base Tunnel encountered so far are much less than those formerly observed in the Rawil exploratory drive and the Gotthard road tunnel. After several years experience, it can now be said that the monitoring system installed in 2000, as well as the close and cooperative collaboration with the power station operators and the controlling bodies of the Swiss government, have proved themselves very well.
On January 1, 2007, of the total of 153.3 km of tunnels, shafts and passages making up the Gotthard Base Tunnel, 102.07 km, or approximately two thirds, had been excavated. In 2006 alone, more than 17 km of the tunnel system under the Gotthard were excavated.
With the foundation stone laying ceremony in Camorino, construction of the Ceneri Base Tunnel officially started on June 2, 2006. Besides other work, preparations for the installation sites at Camorino and Sigirino for subsequent construction of the tunnel are proceeding at full speed.
AlpTransit Gotthard AG
Tel: +41 (0)41 226 06 06
Fax: +41 (0)41 226 06 00
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