Pore size distribution of granular bentonite using MIP and micro-CT

Granular bentonite (GB) consists of millimetre-scale granules, leading to numerous large inter-granular macropores that substantially influence its hydro-mechanical (HM) behaviour. After high-stress HM paths involving soaking of GB samples, undrained unloading under saturated conditions increases the matric suction. Freeze-drying, required before mercury intrusion porosimetry (MIP), removes the liquid phase and alters the inter-granular interactions induced by matric suction, causing macropore expansion that affects the pore size distribution (PSD). Therefore, a simplified methodology combining MIP and X-ray micro-computed tomography (micro-CT) is proposed to characterise the GB’s PSD. Micro-CT images of non-freeze-dried samples allow PSD determination, avoiding the inter-granular pore expansion. The experimentally measured total void ratio was used in CT image processing to segment the pore network used for the 3D MIP simulation of inter-granular pores. Despite limitations associated with the simplified processing steps and the combination of data from both techniques, the methodology provided reliable and systematic PSDs, especially for the inter-granular pores. Thus, the methodology enables correct interpretation of the multiple-porosity network of GB samples and its evolution in HM paths, improving multi-scale understanding of GB’s HM behaviour.