Chapter 8: Analysis and design of shallow foundations

Foundation failures due to seismic shaking have been observed during several major earthquakes in the past. Such failures have occurred in soils susceptible to liquefaction, as well as in soils that did not liquefy. The recent Canterbury earthquakes in New Zealand caused significant bearing capacity failure not only of high-rise commercial buildings but of many residential structures as well. Multi-storey buildings punched into, tilted excessively and slid laterally on softened ground.

The estimation of the magnitude of settlement that a structure will undergo during seismic shaking is therefore an important consideration in performance-based design. Traditionally, most estimations of building settlements induced by soil liquefaction have been based on empirical equations or rules of thumb that were developed to estimate post-liquefaction consolidation settlement for free-field conditions; however, this approach cannot possibly capture shear-induced and localised volumetric-induced deformations in the soil underneath the shallow foundations, which, in turn, are affected by many factors, including building geometry and the properties and conditions of the foundation ground. Moreover, the development of excess pore water pressure that could induce changes in ground motion has not been considered directly in current procedures.