n Journal of the South African Institution of Civil Engineers - Rapid method of selecting raft size for tendering purposes : technical note

Volume 35, Issue 3
  • ISSN : 1021-2019



In South Africa raft foundations, coupled with an articulated superstructure, are often used as an economical solution to reduce the risk of damage to small buildings (with brickwork walls) constructed on expansive soils. Recently, the CSIR developed a new cellular raft foundation (called the BOUCELL), which has an increased stiffness in bending as well as in torsion, with the result that articulation of the superstructure can in most cases be eliminated.

The high variation in the swelling properties and in the climate complicate the design of raft foundations and their implementation is further compounded by the fact that a developer or a building contractor who wants to offer this as an alternative solution needs an early assessment of typical foundation sizes. This early assessment needs to be as accurate as possible to reduce the financial risk involved, but at that stage the available information is generally insufficient for realistic design. A method is presented in this paper that can be used for an early assessment of raft depth, using limited soil data. This method can be used for all types of raft foundations.

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