Box caisson foundation

Fig. 60. Construction process of well foundation Box caisson foundation The box foundation is principally the same as the well foundation, but while the well foundation supports the structure of the building point by point, the box foundation is extending over the the entire footprint of the structure above. The soil is extracted in same way, from the cutting edge within the box foundation. Box caissons can be used up to 40-50 meters depth.

Types of box caisson foundations: • open box caisson, the ground is removed by underwater dredging from the cutting edge; • pneumatix box caisson, a chamber in the bottom fo the cassion serve a workspace for dredging, and the water is pressed out by high air pressure; • the box closed at the bottom and floated on open water to the final position;

A special version of box caisson is the pneumatic caisson, which is usually used below groundwater level or in the construction of bridge piers. In the bottom of cassion a closed workspace is created, by high overpressure in cahmber. The high air pressure displaces the water from the chamber and the soil around the cutting edge can be extracted. In former times the dredging was done by hand, in present days the work is done by machines.

Fig. 61. Bridge pillar construction with pneumatic caisson