Drying-induced volumetric behaviour of clays interpreted via binary pore-scale modelling

The volumetric response upon drying is relevant in the geotechnical and ceramic industry due to the key role played in crack formation. The volumetric response of clays upon drying is relatively complex; the void ratio decreases considerably in the saturated state, levels off almost abruptly at the onset of desaturation, and increases at very low water contents. This paper presents an original deformable pore-network model (DPNM) to elucidate the micromechanisms controlling the complex volumetric response of clays upon drying. The main features of the DPNM are the ‘binary’ approach (pores in the clay are assumed to be either fully saturated with water or dry) and the use of independent tests to calibrate the parameters of the model (compression behaviour of saturated reconstituted clay and dry powder). The DPNM shows that all pores shrink as pore-water tension increases in the saturated state, although the larger pores contribute more to the overall reduction in void ratio. At the onset of desaturation, the larger pores dry out and rebound, whereas the smaller pores remain saturated and shrink. At very low water content/high pore-water tension, the desaturation of the smaller pores causes them to rebound, thus generating a macroscopic increase in the void ratio.