A hydromechanical approach to model shrinkage of air-dried green bodies

This paper presents a simple hydromechanical approach to model drying and shrinkage behavior of clay green bodies. Heat transfer and water vapor flow are neglected but the effect of air velocity, temperature, and relative humidity on evaporation rate can be taken into account through a boundary coefficient. Nonlinear hydraulic and mechanical constitutive functions are introduced and derived from experimental tests at the ‘‘elementary’’ volume scale. A state-of-the-art tensiometer capable of measuring the tensile stress of water up to 2000 kPa was used to relate changes in volume and water content to the capillary suction, which is generated in the clay by the evaporation process. The proposed approach was validated against free dessication tests involving air-drying of clay bars subjected to isotropic volume change and one-dimensional water flow. Two different methods were used to solve the water flow equation. In the first method, nonlinear hydraulic and mechanical constitutive equations and nonlinear boundary conditions were implemented and the flow equation was solved numerically. The second method consisted in linearizing the flow equation and solving it using an analytical solution. The interest for this second method lies on the reduced number of clay parameters required, which can be obtained from simple routine tests.