When the dredging was completed a geotextile was placed on top of the soil, which was, in turn covered with a metre of sand.

Some 18m of soft soil consolidation had to take place, a process which Boskalis accelerated by using the innovative BeauDrain vacuum consolidation technique. The BeauDrain concept is an innovative combination of existing, proven methods to accelerate the consolidation of soft compressible soils. The system consists of a number of drainage curtains, each including a row of vertical wicker drains, all connected to a horizontal collection drain installed at 1 to 2m below the top of the compressible strata and connected to a vacuum pump. The liner placed just above the horizontal drain ensures a proper sealing from atmospheric conditions. To install the BeauDrain system a multifunctional plough has been developed which cuts through the ground. A total drainage curtain is installed in one pass;

the vertical drains, the horizontal collection drain and the liner.

BeauDrain increases the bearing capacity of the soil as the vacuum system raises the horizontal and vertical effective stress and hence, increases the bearing capacity of the subsoil. It will also reduce lateral deformations of the subsoil when loaded.

MJInformation No: 22234