The deterioration of strength, stiffness and resistance to the development of permanent deformation, or the reduction in pavement life, with increasing moisture levels is a common observation. Trial pavement studies in which the water content of the construction has been changed and reduced performance observed are quite numerous. In recent years work in Finland has been reported by Korkiala-Tanttu and Dawson (2007) showing the much faster rutting of a test pavement with a high water table than one in which it was lower. In an earlier study by accelerated trafficking, Vuong et al. (1994) found that the life of a crushed-rock base was very dependent on the degree of saturation in the aggregate base course. Assuming a water content for optimal behaviour, then a 5% change increase in relative water content could lead to a 400% reduction in pavement life. Sharp et al. (1999) reported significant deterioration of in-situ moduli values at an accelerated pavement testing site in lat — eritic gravel bases and sub-bases upon wetting (or improvement on drying) by more than a factor of 2. The silty sand subgrade at the test site also changed stiffness to a similar degree.
Thus site studies broadly support the laboratory and theoretical work reported elsewhere in this book. As an example of a particular study of the effects of moisture change on bearing capacity, the following case record is instructive.
