Water-retention characteristics and collapsibity behaviors: comparison between intact and compacted loesses

The compacted and intact loesses with the same dry density and water content are tested to investigate the structural effects on the water-retention characteristics and collapsibility behaviors of loess. The scanning electron microscopy (SEM) tests are carried out to assist in the interpretation of test results. It is found that the air entry value of the intact loess is 75% smaller than that of the compacted loess. This is likely because that the extra-large pores in the intact loess result in pronounced ink-bottle effects. The water-retention curve of the intact loess exhibits larger and smaller hysteresis than that of the compacted loess at suctions ranging from 0.1 to 7 kPa and from 7 to 80 kPa, respectively. This can be explained by the different wetting-drying history experienced by intact and compacted loesses. Similar collapsibility potential is observed for the intact and compacted loesses with high water contents (>18%), whereas the wetting-induced collapsibility of the intact loess is larger than that of the compacted loess with low water content (16%). This is because that the clay bonding in the intact loess results in a more resistant structure. This resistant structure assists in the intact loess to maintain large void ratios during mechanical loading (200 kPa). During soaking, clay bonding is destroyed and significant collapse is induced. In addition, the differences in the yield stress between the intact and compacted loesses increase with the decreasing water content. It is indicated that the resistant structure of the intact loess is enhanced with the decrease of the water content.