The suction method for estimating the shear strength of soils from plasticity data and mositure content has been examined in the light of a wide range of experimental evidence. It is concluded that the method predicts changes in strength of a wide range of soils satisfactorily. The method has been used to quantify the likely changes in mositure content and strength under a range of site conditions. Very wet weather during construction on a poorly drined site reduces markedly the ultimate equilibrium strength of subgrades of low plasticity; equilibrium values are less than half the values associated with construction in dry weather. Heavy clays are much less affected. Deflection studies indicate that the life of a pavement built in very wet weather may be resuced by up to 50 percent of the life expected of a pavement constructed during average weather conditions