Drawdown of groundwater table causes change of net mean stress and matric suction in unsaturated soil and then induces volume change of the soil mass.For four types of soils including sand

silt

clay and soft clay

the empirical relationship between matric suction and void ratio on drying path is established by utilizing the shrinkage curves and the soil-water characteristic curves which are determined through experimental tests.The relationship between net mean stress and void ratio is obtained by utilizing the oedometer curve.Based on test results and the Fredlund elastic volume constitutive model

subsidence of unsaturated soil zone is estimated for different drawdown of groundwater table.Computed results indicate that in total amount of subsidence

the portion of subsidence of unsaturated soil zone cannot be overlooked.The contributions of unsaturated soil zone to total subsidence increases as drawdown increases.