Chapter 76: Pavement foundation design

There have been significant developments in the design of pavements and trackbed for roads and railways in recent years. The latest design specifications take a more rational approach than the traditional recipe method based on experience and offer potential rewards including the wider use of more sustainable materials and reduction in construction thicknesses. While the aims of these developments are valid, it is considered an increasing focus on analysis has also coincided with a reduction in emphasis on the local geology, groundwater conditions and using appropriate construction materials for the prevailing conditions. This is considered a significant failing, and the authors have experienced many examples of design and construction errors resulting from poor understanding of the ground conditions, with some resulting in multi-million-pound legal disputes. This chapter attempts to address this trend and emphasises the importance of properly assessing the subgrade and developing a design that suits the ground conditions present. It gives a brief outline of good current design practice for UK roads and railways, and references are given to some of the key literature available for further reading. The focus is on the design methods developed for motorways and trunk roads (produced by National Highways) and railways (Network Rail) as the majority of research carried out in the UK has been related to these. A brief description of the important considerations for high-speed rail pavement foundations is provided as well as reference materials for pavement applications not specifically covered in this chapter, such as ports, airfields and unsurfaced roads.