Chapter 19: Settlement and stress distributions

This chapter describes the basic steps involved in calculating both the undrained and drained settlement of foundations on clay soils. It is demonstrated that the vertical stress changes beneath loaded areas, derived from simple elasticity, can be used with confidence for this purpose. In contrast, the changes in horizontal and shearing stresses are very sensitive to the assumed stress–strain behaviour and the theory of elasticity is much less reliable for calculating these. The four most common methods for calculating the final settlement are described. The somewhat surprising conclusion is reached that the simple one-dimensional method of analysis is even better than the more sophisticated methods, provided the appropriate soil stiffness parameters have been obtained. Settlements on granular soils are usually small and much of it takes place during construction. Numerous empirical methods have been proposed for predicting the settlement of foundations on granular materials, which lead to a wide range of estimates. A straightforward analysis of the measured settlements of over 200 records has led to a remarkably simple approach relating settlement to bearing pressure, breadth and average standard penetration test blow count, or cone resistance, over the depth of influence.