Linking shrinkage and water retention to the evolution of pore size distribution and connectivity in peat upon drying

Peat is an organic soil that poses significant challenges to engineering practice due to its complex hydro-mechanical behaviour and environmental significance. Increasing climatic stresses threaten infrastructure worldwide, with unprecedented variations in water content inducing shrinkage and degradation. Assessing peat behaviour under unsaturated conditions remains challenging, as it involves large drying-induced deformations and microstructural changes associated with the fibrous fabric and evolving pore size distribution (PSD). This study presents two novel contributions: (a) a comprehensive experimental dataset describing shrinkage, water retention and PSD evolution during isothermal drying, and (b) a physics-based framework that links PSD to water retention by accounting for concurrent capillarity, adsorption and osmosis. The results show that peat is characterised by a wide, continuous PSD, and that shrinkage is closely associated with the evolution of pore size modes during drying. Pore connectivity is explicitly introduced through percolation theory and is shown to be a key factor controlling water retention. Both capillarity and adsorption contribute significantly over strain ranges relevant the engineering practice. Comparable experimental and numerical results suggest that the wilting point may represent a critical threshold for the degradation of peat solids.