Shallow Foundations

A review of the design and performance of spread footings and rafts in relation to the prediction and control of settlement reveals that allowable bearing pressure for a given settlement of shallow foundations on sand and gravel, when estimated from standard or static cone penetration tests, are rather conservative. Based on the present analysis, the bearing pressures could safely be increased by 50%, when the corresponding predicted settlements would vary from approximately 0.8 to 2 times the observed values. The allowable bearing pressures for shallow foundations on clay, when based on the sum of immediate and final consolidation settlements with an allowance for any lateral consolidation and the effects of shearing stresses, usually yield results of sufficient accuracy. More field observations are needed on the contact pressures and stresses in raft foundations to develop a rational method of their design.