Hydro-mechanical behavior of unsaturated intact paleosol and intact loess

Abstract

Many geo-hazards occurred in regions incorporating loess-paleosol sequences. Understanding the hydro-mechanical behavior of unsaturated intact paleosol and intact loess is a prerequisite to address these geo-hazards. So far, the loess has been extensively investigated, while the study of paleosol is rare. This study investigates the unsaturated hydro-mechanical behavior of intact paleosol and intact loess, including water retention, compression, and collapse. The study of intact loess serves as a benchmark for that of intact paleosol. Results show that the intact paleosol and intact loess have similar air entry value (AEV) and average degree of hysteresis in WRC, although the former soil has a 20.2% smaller void ratio and a 38.8% larger clay fraction. This could be attributed to the larger volume of mega-pores (diameter > 360 μm) owned by the intact paleosol, which offset density and clay fraction effects on the AEV and hysteresis in WRC. On the other hand, the intact paleosol has a smaller structure permitted space (i.e. the area bounded by the compression curves of reconstituted and intact specimens) than the intact loess at a given suction. This is because that point-to-point and point-to-face contacts are widely observed between particles in the intact loess, while face-to-face particle contacts dominate in the intact paleosol. The former particle arrangement results in a metastable skeleton, while a stable skeleton is expected for the latter particle arrangement. In addition, the maximum collapse potential of the intact paleosol, which is calculated by the compression curves under suctions of 200 kPa and zero, is 42.8% smaller than that of the intact loess, mainly because of the metastable skeleton of the latter soil.