Determine about the extent of excavation
The extent of excavation depends upon the construction problems like dewatering and uplift. In extreme cases anchoring of the box may be required to prevent uplift of the foundation. Buoyancy rafts can also be constructed by assembling cells on shallow excavations and grabbing the earth from inside open cells. A typical example of such a construction was that of the Grangemouth Refinery where a total of 240 cells were provided in an area of 52 m x 52 m