ABSTRACT

The Ring Rail Line is an important circular route of the Helsinki Metropolitan Area. It is an urban rail line and a rail connection to the Helsinki-Vantaa airport. During excavation works under the Helsinki-Vantaa airport vague liquid substance was found to leak into the tunnel. The fluid contains nutrients that enable the growth of microbes which produce distinctive smell related to anaerobic processes. The investigations proved that the fluids were aggressive and harmful to cement based and steel structures. It was decided that an isolation structure was needed for the railway tunnels and part of the railway station to protect normal tunnel structures. Extensive grouting was to be done before construction of isolation structures. Isolation structures needed extra space in the tunnel. Therefore, the tunnel needed to be enlarged.

To prevent leakages to the railway station and railway tunnels a massive post-grouting program was performed. As the fluid was very acidic cement based materials were not to be utilized. Instead chemical, polyurethane-based materials were used. Prior the post-grouting extensive pre-grouting was done but is was insufficient in sealing all the cracks to prevent the glycol fluids from entering the tunnel.

The plan was to create a grouted "umbrella" around the station hall and the railway tunnel. There is a natural higher formation in the rock surface on the eastern side of the leakage area. The formation was thought to help contain the fluids in the depression area.

The grouting worked well. After about half the grouting was done, detrimental fluids were observed further away than before any grouting efforts. This led to the need to either expand isolation structures or prevent further migration using more grouting.

A grouted vertical barrier was chosen to prevent further migration. This strategy was effective as the migration was stopped and aggressive fluids have led to leak into drainage system of isolation structure. The barrier was grouted using microcement.

Seven years after grouting no new leakages of detrimental fluids have been found beyond the barrier. The grouted barrier works as designed.

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