Observation of peat porosity and water retention upon drying

Peat is a highly organic material that poses significant environmental and geotechnical engineering challenges due to its hydrological relevance and atypical mechanical behaviour. Understanding its unsaturated response is essential for infrastructure built over organic soils, particularly under increasing seasonal variability associated with increased climate stresses. Modelling the water retention behaviour of peat remains complex due to its high compressibility and the fabric rearrangements induced by drying and wetting cycles. This study presents an experimental characterisation of the shrinkage and water retention behaviour of natural and reconstituted fibrous peat from the Netherlands. A combination of high-resolution laser scanning and suction measurements was employed to monitor volume change and water retention throughout drying. The results are interpreted through a framework that distinguishes between inter- and intra-ped porosities, allowing for the separation of their respective contributions to shrinkage and retention. Complementary mercury intrusion porosimetry (MIP) analyses provided insight into the evolution of pore size distribution during drying, supporting the interpretation of a sequential engagement of pore sizes. The findings underscore the importance of accounting for differential multiscale porosity evolution and fabric structure when evaluating the hydro-mechanical response of peat.