3.3.5 Density and Moisture Content
The effects of compacted layer properties (i.e. density, moisture content and particle orientation or degree of anisotropy) on granular modulus are very significant. For low plasticity crushed rocks, moduli increase significantly with density up to 100% of Modified Maximum Dry Density (MDD) (Vuong, 1992). However, at higher densities, there is little change in modulus, particularly at low moisture contents. At high degrees of saturation (say above 80%), the combination of a high degree of saturation, poor drainage and low permeability could produce high pore pressure (or low effective stress) and, consequently, low modulus. It should be noted that these effects may vary according to material type and further studies on the effects of manufactured layer properties for different materials are required, particularly at different stress levels.
In the design of a flexible pavement it is imperative that the layers have adequate modulus to spread (reduce) the applied stresses and strains to the subgrade without unacceptable permanent surface deformation. Part 2: Pavement Structural Design of the Guide to Pavement Technology includes a relationship to estimate the allowable loading in terms of total permanent deformation of unbound granular materials and subgrade.