It is well known that the hydromechanical behavior of both saturated and unsaturated loess soils is significantly influenced by the soil fabric. However, there is limited understanding of how the soil fabric or structure evolves due to mechanical, hydraulic and chemical changes on loess soils. Information of the microstructural evolution or change in pore-size distribution (i.e., PSD) of loess soils along different stress paths is valuable for proposing an advanced constitutive model that considers the microstructure and can better model the hydromechanical behavior of loess soils. For this reason, in the present study, the microstructure is characterized on intact and saturated loess specimens before and after oedometer consolidation tests, using scanning electron microscopy and mercury intrusion porosimetry methods. The results suggest that the loading-induced change in PSD varies with stress level and saturation state of the loess soil. A reduction arises in the cumulative intrusion void ratio due to an increase in vertical stress, which accounts for compression of inter-aggregate pores greater than 6 μm. However, loading saturated loess leads to transformation from a bimodal PSD into a trimodal one that defines three major pore series, namely large-pore series (i.e., more than 6 μm), medium-pore series (i.e., between 0.1 and 6 μm) and small-pore series (i.e., less than 0.1 μm). The trimodal nature of PSD is, however, destructed under higher vertical stresses. Both large pores and medium pores are compressed under higher vertical stresses (i.e., > 600 kPa). The inundating-induced change in PSD is dependent on loading condition and can be discerned to take place in the same three pore series. Not only large pores but also medium pores collapse upon inundating under higher vertical stresses (i.e., > 600 kPa). The microstructural evolution is consistent with the mechanical responses of both intact and saturated loess.

中文翻译：

---

荷载和淹没引起的湿陷性黄土孔径分布的变化

众所周知，饱和和非饱和黄土的水力学行为都会受到土壤结构的显着影响。然而，对于由于黄土土壤上的机械，水力和化学变化而导致的土壤结构或结构如何演变的认识有限。黄土沿不同应力路径的微观结构演化或孔径分布（即PSD）变化的信息对于提出一种先进的本构模型，该模型考虑了微观结构并能更好地模拟黄土的水力力学行为，具有重要的价值。因此，在本研究中，使用扫描电子显微镜和压汞法测量了饱和的黄土样品在里程计固结测试之前和之后的显微结构。结果表明，加载引起的PSD变化随黄土的应力水平和饱和状态而变化。由于垂直应力的增加，累积的侵入空隙率降低，这说明聚集体间孔的压缩大于6μm。然而，加载饱和黄土导致从双峰PSD转变为三峰PSD，后者定义了三个主要的孔隙系列，即大孔系列（即大于6μm），中孔系列（即0.1至6μm）和小孔系列（即小于0.1μm）。但是，PSD的三峰性质在较高的垂直应力下被破坏了。大孔和中孔都在较高的垂直应力（即> 600 kPa）下被压缩。PSD的淹没引起的变化取决于加载条件，可以看出发生在相同的三个孔系列中。在较高的垂直应力（即> 600 kPa）下浸没时，不仅大孔隙而且中等孔隙也会塌陷。微观结构的演变与完整和饱和黄土的力学响应是一致的。