The blanket raft foundation is a curst raft constructed on a stone blanket, which is built up in layers on the reduced sub-strata level.
The basis of the action and design of the foundation is a composite action between the crust raft and the stone blanket.
In order to disperse and support loading, where there may be localized disparity in the sub-strata, the curst raft and the blanket interact to span over the weaker soil spots. The stone blanket is an effective method of dispersing heavy imposed surface loading, especially edge loads or where there is an imbalance of load with soft spots in the sub-strata.