Microstructure and soil-water retention behavior of compacted and intact silt loess

There are an increasing number of mega engineering projects of removing the top of hills to fill in the valley for new land creation in the Loess Plateau of China, which significantly changes the hydrological and geological equilibrium state of the site. The formation of a new hydrological equilibrium state is associated with the water movement in the compacted and intact loess layers. Most disasters occurring in the loess area are related to water. The soil-water retention curve (SWRC) is the key to the implementation of unsaturated soil mechanics in engineering practice and is required to numerically model the movement of water in the soil. In this study, the SWRCs and microstructure of intact and compacted specimens from Lanzhou and Yan'an, two typical cities that have new land creation projects, are investigated. The SWRC is obtained using the filter paper method. The mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) techniques are used to explore the microstructure. The results highlight that the intact loess has a higher air occlusion value (AOV) and a similar slope of SWRC in the transition zone compared with the remolded specimens that compacted at the natural water content. The normalized SWRC (i.e., degree of saturation versus suction/AVO) of the intact specimen is approximately the same as the remolded specimens compacted at the natural water content. The difference in the microstructure between intact and compacted specimens originates from different existing states of the clay particles and further contributes to the variation of the SWRC.