Abstract:
Pneumatic sinking of caissons is already known from mid-19th century. In the 20th century quite some
safety improvements have been developed supported by research. The technique of pneumatic sinking
has been applied on many projects for underground construction till depths over 20m under
groundwater level. But human labour was still needed despite all improvements on equipment.
Volker Staal en Funderingen, a known deep foundation contractor in the Netherlands, obtained 2
contracts in 2015 for sinking in total 4 caissons in Hamburg (Germany) and near Amsterdam (the
Netherlands). The latter concerned 2 door chambers for world’s largest sea-lock, one of them 55x81
m2 (180x266 ft) till a depth of 25.5 m (84 ft). This would mean a world record for pneumatic sinking!
However from depths deeper than 9 m (30 ft) the effective working time is heavily reduced due to
decompression limitations and from 16 m (50 ft) even heavily reduced.
It was decided to develop a remote controlled process, including the necessary equipment from
scratch. Monitoring not only of the essential process devices but also of the structural behaviour of the
sea-lock was essential for approval of this execution method. Due to lay-out and the sizes of the
largest caisson the structural integrity was extremely critical for torsion and bending moments. A
displacement controlled execution by the observational method was therefore required. In engineering
a new approach for modelling the semi-continuous failure mechanisms of the soil was needed to
understand the sensibility of the excavation process and to define limit values for the execution.
In the paper a short history of pneumatic sinking will be given before the structural and geotechnical
issues will be explained combined with the experiences during the execution.