Investigation of porosity variation on water retention behaviour of unsaturated granular media by using pore scale Micro-CT and lattice Boltzmann method

• Published in: Journal of hydrology (Amsterdam) 2023-11, Vol.626, p.130161, Article 130161
• Main Authors: Wang, Ji-Peng, Liu, Tai-Heng, Wang, Shao-Han, Luan, Ji-Yuan, Dadda, Abdelali
• Format: Article
• Language: English
• Subjects: Contact angle; Granular media; LBM; Unsaturated soils; Water retention curve; X-ray microtomography
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2023.130161

•The desaturation process of granular media was explored through CT scanning and MCMP-LBM simulation.•The water retention capacity of granular media is inversely proportional to both the porosity and contact angle.•The wetted ratio of the solid surface shows a negative correlation with the contact angle and a positive correlation with the porosity.•Under low saturation conditions, LBM simulation has a distinct advantage over CT scanning. Most soils in nature are in unsaturated states. The key to correctly understanding its hydraulic characteristics lies in mastering the correlation between its microstructure and macro water retention characteristics. Based on an independently developed miniaturized in-situ unsaturated soil–water characteristic instrument, three-phase topological morphology and micrographic information (pore throat, liquid cluster, interface area) of unsaturated granular media were explored, supplemented by CT scanning under a high resolution (5.6 μm/pixel). In addition, three-dimensional reconstruction of CT images was performed for simulating two-phase flow in porous granular media using the lattice Boltzmann method. The experimental results indicate that the water retention capacity, air-entry value, and residual saturation of unsaturated granular specimens are negatively correlated with the porosity of specimens. As the saturation decreases, the specific air–water interfacial area first increases and then decreases, with the peak value appearing around 20% of saturation. Based on LBM simulation, the water retention capacity of the specimen is negatively correlated with the contact angle, while the liquid–solid characteristic interface area and relative permeability are positively correlated. The experimental and simulation results demonstrate good consistency with each other.