Permeability of loess from the South Jingyang Plateau under different consolidation pressures in terms of the three-dimensional microstructure

Multiple consolidation-permeability tests were performed on loess samples from the South Jingyang Plateau in northwest China to analyze permeability under actual stresses. Three-dimensional microstructures for loess samples under each consolidation stress were established based on high-resolution computed tomography images to thoroughly interpret the permeability variation in terms of the loess microstructures including the pores and throats. With increasing consolidation pressure, the permeability decreased greatly at the beginning and tended to become stable. In the stage of dramatic decrease in permeability, pore coordination number decreased slightly under pressure, indicating little influence of connectivity among pores on permeability. The pores in the range of 14 to 25 mu m decreased by 10.1% in volume percentage, and the pores larger than 13 mu m decreased by 19.6% in number. Accordingly, throats larger than 6 mu m decreased by 13.1% in area percentage, and throats larger than 2 mu m decreased by 14.9% in number. Throat size distribution played a decisive role in permeability, pore size distribution acted as a bridge to influence permeability, and only the spaced pores and some interaggregate or intergrain pores larger than 13 mu m that allowed free water to pass were related to permeability. The decreases in these relatively large pores and throats caused considerable decreases in permeability. However, the existence of large throats, even large numbers of such throats, does not mean high permeability, which can be verified in the stable stage of permeability. This research provides a better understanding of loess permeability in terms of three-dimensional microstructure and further insights into the stability analysis of loess slopes and the control of other hazards in loess regions.