Chapter 53 Shallow foundations

The design of shallow foundations is exceptionally wide ranging, and can vary from simple strip footings for a lightly loaded domestic property to the design of a large raft for a nuclear power station. The likelihood of geohazards affecting a site must always be assessed, irrespective of the scale of the project. This is best assessed by a comprehensive desk study and a site walkover by an appropriately experienced specialist. The prime requirement for successful design and construction is an understanding of the site history and the ground and groundwater conditions across the site. Sophisticated analysis will not compensate for a lack of knowledge of these issues. Prior to detailed analysis it is worthwhile considering the likely behaviour of the whole structure (which may comprise multiple closely spaced strip or pad footings) in the context of the overall geology, adjacent structures and the site topography. The potential risk of adverse interactions within, beneath and around the proposed structure should be considered. Foundation settlement will often be a more critical consideration than bearing capacity. Simple methods of analysis are usually adequate; the biggest challenge is to make reliable estimates of the compressibility of the ground. The bearing capacity and settlement of rocks will be sensitive to the orientation, spacing and characteristics of discontinuities in the rock mass, the degree of weathering and voids (either natural or man-made).