STABILITY OF DUAL POROSITY SOIL SLOPE AGAINST RAINFALL-INDUCED SLOPE FAILURE

Abstract

Slope stability and landslides are caused by a combination of factors, including prolonged rainfall, groundwater level, slope geometry, and the geological structure of the soil have significant influences on the stability of the slope. However, a few studies have been conducted on rainfall's influence on slope stability with bimodal soil-water characteristic curves or dual-porosity soil. Therefore, the aim of this research is to analyze the stability of dual-porosity soil with various geometries under extreme rainfall in Kazakhstan. In this study, comprehensive laboratory tests were carried out to obtain index properties, saturated permeability, saturated shear strength, the bimodal soil-water characteristic curve (SWCC), and unsaturated permeability of silty sand and sandy silt. The first and second air-entry values and inflection points of silty sand are Ѱa1 = 1 kpa and ѱa2=10 kpa Which are lower than those of sandy silt: Ѱa1=3kpa and ѱa2=25kp. The slope of sub-curve 1 of silty sand is σ1=0.5 higher than those of sandy silt σ1=0.36-. The unsaturated permeability of sandy silt is 7.00E-5 which is higher than that of silty sand at 9E-7 m/s. Comprehensive numerical analyses were performed on dual-porosity soil slopes with different geometries under extreme rainfall intensity in Kazakhstan to generate variations of the factor of safety (FoS) and a decrease in pore-water pressure with time. The results indicate that the factor of safety for the shortest slope and the gentlest slope is higher than the tallest slopes with the steepest angles. It was observed that the slope with dual-porosity soil can only be constructed up to 10m and 20m slope heights and 27–35 ° slope angles since the minimum FoS for this slope geometry is FoS=1.27>1.25 (higher than the minimum FoS considered as stable slope)