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Rain-induced shallow failures in expansive soils often occur on gentle slopes with slope ratios of 1:2–1:6, resulting in highly complex stability issuesThis study established an equivalent theoretical model for the swelling behavior of expansive soils based on the similarity theory of temperature and humidity fields. A numerical simulation approach was developed using a model with consistent nodes and the conversion of seepage results and swelling loads, allowing for the decoupling analysis of slope seepage–deformation–stress considering swelling and strength softening. Numerical analyses were conducted on a specific slope profile in a case study, analyzing the distribution and evolution of the slope seepage, deformation, and shear stress. The findings revealed that changes in moisture content at the slope toe have the most significant impact, with infiltration depth and strength attenuation being the largest. Horizontal and vertical deformations were also highly influenced by the reduction of shear strength. The uneven water absorption and swelling of expansive soil slopes resulted in shear stress concentration areas on the slope, leading to local failures near the slope toe and eventual overall instability of the slope. This study provides valuable insights into the complex behavior of shallow failures in expansive soil slopes. [ABSTRACT FROM AUTHOR]

In nature, expansive soil is generally in a state of swelling during rainfall, and its soil–water characteristic curve (SWCC) exhibits a three-dimensional space shape under the action of an increasing void ratio. In this study, expansive soil from Hefei, China, was used. SWCC and hygroscopic tests were performed. A three-dimensional hygroscopic swelling mathematical model of the dry density–void ratio–saturation degree was constructed based on the volume change behavior of expansive soils resulting from the hygroscopic test. In addition, depending on the variation in suction with the saturation degree of expansive soil under different values of dry densities, an SWCC mathematical model considering the swelling effect was constructed. The three-dimensional surface model of the hygroscopic swelling of the expansive soil was steeper in the lower saturation degree area. As the saturation degree increased, the three-dimensional surface gradually became flat. The SWCC model of the expansive soil under the action of swelling in a three-dimensional space is an S-shaped surface. The model exhibited dynamic changes in the suction and saturation degrees as the dry density of the soil decreased continuously. The model comprehensively revealed the hydraulic and swelling properties of expansive soil. [ABSTRACT FROM AUTHOR]

Aiming to resolve the engineering hazards caused by the long-term micro-swelling of red-bed mudstone, gaseous moisture absorption-swelling tests under four ambient humidities were conducted (60%, 70%, 85% and 99%) by developing a set of experimental devices. Based on the moisture absorption characteristics of mudstone, the effects of a vapor pressure gradient on the equilibrium time, moisture absorption rate and swelling rate were discussed. Combined with its mineral composition and pore structure, the correlation mechanism between gaseous moisture absorption and swelling was explained in depth. The experimental results suggested that the whole process was long-term and slow. The swelling rate was lower than the moisture absorption rate by two orders of magnitude. As a result, the duration of a stable swelling strain was two orders of magnitude higher than that of a stable moisture absorption. The characteristic curve of moisture absorption went through three stages: the rapid stage, dominated by crystal layer adsorption; the intermittent expansion stage, dominated by adsorbed water film; and the decelerated stage, dominated by capillary condensation. In the intermittent expansion stage, as the relative humidity declined, the duration of an intermittency increased, and the number of intermittencies decreased. The evolution of the swelling rate obviously lagged the proportion of moisture absorption. This hysteresis effect reached its maximum when the moisture absorption transitioned from the intermittent expansion stage to the decelerated stage. Moreover, the equilibrium time, moisture absorption ratio and swelling strain all had a non-linear proportional relationship with the relative humidity. In this case, the critical value was 85%. Finally, a unified mathematical expression for the gaseous moisture absorption curve was acquired and the relationship between the swelling strain and the increment of moisture content was fitted; this will provide the necessary research basis for a subsequent simulation of its volume change under changing ambient humidity. [ABSTRACT FROM AUTHOR]