Performance parameters and target values for construction of UK road foundations

There is impetus in the UK to move away from empirical design of road foundations and method specification towards analytical design assured by end product testing during construction. Current research at Loughborough University, sponsored by the Highways Agency, is aimed at introducing such a performance based specification. This paper introduces the philosophy behind the research and explains the primary objectives. Selective results are presented from a full-scale field trial construction of a road foundation on a soft subgrade, which was characterised by a variety of field devices and subsequently trafficked. This paper focuses on insitu stiffness modulus (ER), measured by several devices for comparison. The setting of suitable target values for field ER is seen as a key factor and the influence of inherent variability in material response a concern. The discrepancy between devices and the problem of long-term stability are discussed and highlighted as a key focus for the remainder of the work.