Characterization and comparison of 3D pore structures and their changes during collapse in Chinese loess and pore classification in terms of collapsibility

The pore structure of loess greatly influences its collapse potential and other engineering properties. In this study, the pore structures of Malan loess from Lanzhou (LZ), Qingyang (QY) and Jingyang (JY) and their changes during collapse were characterized and compared through microcomputed tomography (mu -CT) scanning and mercury intrusion porosimetry (MIP) test. The correlation between pore structure and collapse potential was addressed, and a pore classification was ultimately suggested. The results indicate that the LZ loess has a more homogeneous pore structure with inter-skeleton particle pores and spaced pores than the QY and JY loesses with primary inter and intra-aggregate pores and constricted pores. During collapse, pores larger than 35 mu m changed into smaller pores, accompanied by a decrease of entrance pores larger than 8 mu m in the three loess samples. The pores change in size through two major ways, one is that skeleton particles slide and rearrange, causing the collapse of inter-skeleton and spaced pores and a decrease or closing of pore channels (i.e., for LZ loess). The other is that clay buttresses swell and disperse in the inter-aggregate pores, separating large pores into smaller ones, and forming a more homogeneous pore structure and more pore channels (i.e., for QY loess and JY loess). The dominant inter-skeleton particle pores and the large mean pore size in the LZ loess contribute to its greatest collapse potential. Based on the discrete pore size distributions and their changes, 10, 35 and 80 mu m were selected as boundaries for pore classification in terms of collapsibility.