A raft design method for swelling clay

Stiffened raft foundations often prove to be the most economical solution to the construction of small buildings on potentially swelling soil profiles. Various raft design methods have developed in the past, but being empirical imply that they may only apply to local soil and climate conditions. Pidgeon (1988) developed a method (also empirical) that can applied to South African conditions. An alternative design procedure has been developed and presented in this paper. In this procedure, the “hang-off” distance is calculated based on the predicted differential heave, the weight of the structure and the heave suppression properties of the clay. The total and differential heave prediction is based on the predicted soil suction distribution and the swell properties of the soil profile.