Grain breakage_induced evolution of grain size distribution, pore structure, and permeability of sands under high oedometric stress

Abstract

Grain breakage under high stress conditions can significantly affect the hydro-mechanical behavior of granular materials by altering grain size distribution, pore structure, porosity, and permeability. This study investigates these coupled effects in two sands with contrasting mineralogical characteristics, namely Hostun silica sand and carbonate sand, subjected to high oedometric stresses up to 105 MPa. High-pressure oedometer tests were performed on dense specimens prepared at a relative density of approximately 0.9. Grain size distribution was determined by post-loading sieve analysis, while permeability was measured at different stress levels using a constant-head system connected to the oedometer cell. Pore-access size distribution was characterized using two complementary techniques depending on material response and stress level: the tensiometric method, based on drying-path water retention measurements and the Young–Laplace law, and mercury intrusion porosimetry for carbonate sand specimens that developed sufficient cohesion after high-stress loading. The results show that increasing stress induces progressive grain fragmentation, leading to an evolution of the grain size distribution toward an ultimate grading state, together with reductions in pore size and porosity. The crushing threshold was identified at approximately 12.5 MPa for Hostun sand and 3 MPa for carbonate sand, indicating the strong influence of mineralogical composition on breakage resistance. Permeability decreased markedly with stress, with a reduction of about 50 % for Hostun sand and more than 70 % for carbonate sand. This stronger reduction in carbonate sand is associated with more pronounced particle breakage, pore structure modification, fines production, and reduced pore connectivity. The experimental results were interpreted using the Continuum Breakage Mechanics framework, and a power-law relationship between permeability and porosity was calibrated for both sands. The analysis indicates that grain rearrangement and grain breakage jointly control porosity and permeability reduction, with the influence of grain breakage becoming increasingly significant at higher stress levels, particularly for carbonate sand.These findings provide an experimental and modeling basis for understanding the coupled effects of high stress, grain breakage, pore structure evolution, and permeability reduction in sands, with implications for geotechnical, geomechanical, and petroleum reservoir engineering applications..