Effect of Unimodal and Bimodal Soil Hydraulic Properties on Slope Stability Analysis

Rainfall infiltration is the primary triggering factor of slope instability. The process of rainfall infiltration leads to changes in the water content and internal stress of the slope soil, thereby affecting slope stability. The soil water retention curve (SWRC) was used to describe the relationship between soil water content, matric suction, and the water retention characteristics of the soil. This characteristic is essential for estimating the properties of unsaturated soils, such as unsaturated hydraulic conductivity function and shear strength. Thus, SWRC is regarded as important information for depicting the properties of unsaturated soil. The SWRC is primarily affected by the soil pore size distribution (PSD) and has unimodal and bimodal features. The bimodal SWRC is suitable for soils with structural or dual-porous media. This model can describe the structure of micropores and macropores in the soil and allow the hydraulic behavior at different pore scales to be understood. Therefore, this model is more consistent with the properties of onsite soil. Few studies have explored the differences in the impact of unimodal and bimodal models on unsaturated slopes. This study aims to consider unimodal and bimodal SWRC to evaluate the impact of unsaturated slope stability under actual rainfall conditions. A conceptual model of the slope was built based on field data to simulate changes in the hydraulic behavior of the slope. The results of seepage analysis show that the bimodal model has a better water retention capacity than the unimodal model, and therefore, its water storage performance is better. Under the same saturated hydraulic conductivity function, the wetting front of the bimodal model moves down faster. This results in changes in the pressure head, water content, and internal stress of the soil. The results show that the water content and suction stress changes of the bimodal model are higher than those of the unimodal model due to the difference in water retention capacity. Based on the stability of the slope, calculated using the seepage analysis, the results indicate that the potential failure depth of the bimodal model is deeper than that of the unimodal model.

Effect of Synthetic Detergents on Soil Erosion Resistance

The effect of soil contamination with synthetic detergents (SD) Labomid-203, MS-8 and ML-51 in combination with potassium monoborate (MBP) on the change in the potential of soil erosion resistance (PER) was evaluated. PER characterizes the soil resistance to water erosion and is equal to the energy of a water jet acting perpendicular to the soil surface, required for the destruction and removal of a unit of soil mass from the area of its natural occurrence. Soil water retention curve (SWRC) and hydraulic conductivity were selected for the research as parameters determining soil erodibility. SWRC and moisture conductivity function are dependent on the surface tension and viscosity of the moisture in the soil, which are changed on soil contamination with surfactants of washing solutions. Integrating the expression for SWRC in the range of moisture content values from a fixed initial value to the value, corresponding to the complete filling of soil pores with moisture, gave the result correlating with the energy determining the potential for erosion resistance. Soil contamination with SD and MBP led to the significant decrease in soil erosion resistance, which is particularly evident at low moisture values. The largest decrease in soil erosion resistance (by an average of 39.6%) was caused by MS-8 (1.0% MS-8, 0.3% MBP). The smallest decrease in soil erosion resistance (by an average of 12.4%) was caused by ML-51 (0.5% ML-51, 0.1% MBP). The experiments were carried out with dark-gray and light-gray forest soils of the Chuvash Republic (Russia).