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.