Following a two week suspension due to insurance concerns in November on the AlpTransit Gotthard Base Tunnels project, a significant milestone was reached just before the Christmas shutdown with overall completion of tunnelling work on the mega project reaching approximately 40% of the 153km total to be tunnelled.

The two 9.58m diameter Amsteg TBMs in the east and west tunnels reached the halfway point of the 11.35km section between Amsteg and Sedrun. The Herrenknecht machines, Gabi I and Gabi II, reached the halfway point within 19 days of each other between 17 November and 6 December. There remains 5.4km to be excavated in the east tunnel and 5.6km in the west.

The Amsteg machines had set project monthly driving progress records with a combined total of 1.3km in the latter quarter of 2004, but perversely, this was not a happy achievement. The TBMs were hitting daily advance rates of 20 metres, with daily performance peaking at 30 metres. As a consequence the dust concentrations and air temperatures around both TBMs exceeded the allowed limits. The maximum permissible value for quartz dust on the contract is 0.15mg per cubic metre and the temperature limit is 28ºC.

A meeting was held on 2 November between AlpTransit Gotthard Ltd., the Amsteg Lot 252 Gotthard base Tunnel North (AGN) consortium and the Swiss Accident Fund (SUVA). It was decided to temporarily suspend mechanical driving in both tunnels pending AGN implementing mitigation measures to get the dust and temperature values back within limits in order to safeguard the tunnellers’ health.

On 9 November, the TBMs were restarted to allow readings to be taken of conditions following improvements to ventilation and dust extraction systems. SUVA took extended readings in the tunnels on 11 November and temperature readings were within tolerances. Quartz dust concentration in the west tunnel was below limits and slightly above at some locations in the east tunnel.

An agreement was reached whereby AGN were allowed to resume driving subject to all conditions being complied with by 24 November.