ABSTRACT
Within the UK, research has been carried out on behalf of the Highways Agency by the Transport Research Laboratory (TRL) and other organizations to develop a performance based specification for road foundations. Chaddock & Brown (1995) described research on the in-situ assessment by various tests of composite foundation structures that incorporated unbound granular sub-base and, if used, capping on the underlying soil. This research led to outline proposals for a performance based specification for road foundations. Fleming & Rogers (1999) described similar work for the underlying earthworks to develop a draft performance based specification for capping and subgrade. Chaddock and Merrill (2004) reported further developments of the individual test techniques and procedures to ensure compliance of the road foundations at construction. They suggested the establishment of various classes of foundations that are defined by their stiffness and offer different degrees
of structural support to the overlying pavement. It was asserted that lower class foundations with the lower pavement support or stiffness could be built with unbound granular materials, whereas higher class foundations of higher pavement support or stiffness would require construction with hydraulically bound materials in their upper layers. Thinner pavements were proposed for the higher quality foundations. The main features of a proposed performance based specification for standard as well as superior foundations were outlined.
