This study aims to establish a generalized water-retention model by correlating model parameters with fundamental physical indexes of loess. Water retention test data from 35 sources of loess soils in northwest China were optimally fitted to yield parameters for the generalized water retention model (the Zhou-Lu model). These loess soils, classified as lean clay, encompass a broad range of particle size distribution (8.60%–37.85% in clay content), plasticity index (7.20–17.00), and dry density (1.23–1.83 g/cm³). Spearman correlation analysis between model parameters and both single and synthetic physical indexes indicates significant correlations of maximum adsorbed water content w_amax with fines content P_fine, air-entry value 1/α with wI_Pe (the product of weighted plasticity index wI_P and void ratio e), and capillary pore size distribution n with plasticity index I_P, which were respectively described as simple empirical functions. The other three parameters (maximum matric suction ψ_max, adsorption strength parameter m, mean cavitation suction ψ_c) are highly indeterminate and lack experimental evidence; therefore, the means were taken from their statistical distributions. The above parameters were incorporated into the Zhou-Lu model. Deviations of model predictions from the dataset mostly fall within ±30%. Further verification, based on water retention test data of compacted loess from three sampling sites (Baishui, Jingyang, and Hengshan), confirmed the rationale of the model. This preliminarily indicates the robustness of the Zhou-Lu model for loess soils with diverse textures, and allows for further refinement given improved datasets.

In loess formations, multiple layers of reddish ancient soil often alternate. Due to their relatively high hardness, they are resistant to collapsing when exposed to water, which significantly impacts the measurement results of the collapsibility of loess formations. However, there is currently a lack of research on the controlling role of ancient soils in collapsibility, leading to a lack of theoretical basis for making scientific decisions on the collapsibility of geological formations.To address this gap, this study compiled the results of inundation tests in the Loess Plateau region, analyzed the indoor and outdoor differences in collapsibility characteristics in different areas, and focused on large-scale inundation tests in two experimental sites in Xi'an. Various aspects were measured under different test conditions, including moisture diffusion in the soil, moisture content changes, soil pressure variations, and cumulative collapsibility.The final results indicate that paleosollayers hinder the collapsibility process by impeding water infiltration and preventing the transmission of deep-seated collapsibility to the surface. This leads to a positive correlation between the measured collapsibility values and the number of ancient soil layers. This study aims to provide insights into the self-weight collapsibility mechanisms in loess formations where ancient soil layers are commonly found.

The loess with different thickness is in the humid-thermal coupling environment of rainfall-evaporation for a long period of time, which is very prone to induce the generation of cracks in the loess, significantly weakening the structural and integrity of the loess, thus affecting the construction of the project area. Therefore, it is necessary to study the effect of soil thickness on the cracking characteristics of loess under the action of wet dry cycles. In this paper, a series of indoor wet dry cycle tests were carried out to record the water content change and crack development of the specimens in real time, and the crack network was analyzed by using digital image processing technology combined with fractal dimension. The test results show that: the different evaporation paths and water contents lead to inconsistent water evaporation rate of the soil, and the greater the thickness of the loess, the slower its water evaporation rate; interfacial friction affects the cracking process of the soil, and the thicker the soil, the slower the development of cracks, and the lower the complexity of the crack network. As drying proceeds, the interfacial friction gradually decreases and the soil shrinks significantly. The dry-wet cycle effect will lead to the reassembly of soil particles, accelerate the water evaporation process, and the soil surface will deteriorate continuously. The results of the study can provide some guidance for the prevention and control of geologic hazards in the Loess Plateau region.