Works are aimed at waterproofing the area between the foot of the sheet pile and the rock by means of jet grouting columns, namely along the perimeter neighbouring the former Barkarby military airfield, in the municipality of Stockholm, Sweden.
Waterproofing was carried out in order to seal the area under which the entrance to the metro tunnel will be built, in order to extend the current route from Akalla to Barkarby.
The treatment involved a minimum overlapping of 100 cm above the foot of the sheet pile at the top and at least 50 cm deep into the rock at the bottom.
In order to improve the connections and cut journey times by public transport, it was decided to extend the Blue Line of the metro that will connect Akalla and Barkarby. Two new stations will be built, one located in the emerging Barkarby district and the other near the former Barkarby military airfield. The entrance to the metro will be close to the airfield.
The waterproofing between the lower edge of the sheet piles and the rock took place by means of jet grouting columns using the single-fluid jet technique, and employing Soilmec SM-20 drilling rigs. A Soilmec SM-28 rig was instead used for the pre-drilling phase.
At the end, the average length of the columns was 2.4 m with a 10.50 m average installation depth. Columns with a diameter of 1000 mm have a 600 mm long centre-to-centre distance, i.e., the average column for a sheet pile.