[Objective] The primary objectives of this study were to fundamentally characterize the microstructural, compositional, and physical attributes of the region’s expansive soils, to quantitatively identify the causal factors and failure modes behind recurrent slope failures through advanced numerical simulation, and to synthesize these insights into a robust, comprehensive treatment strategy. The research seeks to establish a definitive, cause-effect relationship linking the intrinsic micro-scale properties of expansive soil to its macro-scale mechanical response and instability, thereby offering a scientifically grounded and practical framework for slope stabilization in expansive soil regions, which is of paramount importance for the safety and longevity of large-scale irrigation projects. [Methods] Laser particle size analysis was performed to determine the detailed particle size distribution; scanning electron microscopy (SEM) to visually examine the microstructural morphology and fabric of the soil; and energy-dispersive spectroscopy (EDS) for qualitative and quantitative elemental composition analysis. Furthermore, basic physical and index properties, including dry density, natural water content, liquid limit, plastic limit, plasticity index, and free swell ratio, were measured. A finite element model of a representative canal slope was constructed using MIDAS GTX-NX. This model incorporated the Mohr-Coulomb constitutive relation to represent soil behavior and applied the strength reduction method to accurately identify potential slip surfaces, compute the factor of safety under natural conditions, and analyze the associated displacement and strain fields. [Results] Particle size analysis revealed a poorly graded soil with grain sizes predominantly concentrated in the 10-100 μm range (fine silt to clay), with characteristic diameters D₁₀, D₃₀, and D₆₀ being 12.364, 24.146,49.236 μm, respectively. The calculated uniformity coefficient (C_u) of 3.982 and curvature coefficient (C_c) of 0.957 definitively classified the soil as poorly graded, indicating a structurally loose arrangement with high porosity and susceptibility to structural collapse upon hydrological changes. SEM imagery confirmed a heterogeneous microstructure composed of irregular, angular particles with a loose, flocculated fabric and well-developed pores, which facilitates easy water ingress and weakens interparticle bonds. EDS analysis quantitatively identified the primary elements as Oxygen (51.16%), Silicon (25.97%), and Aluminum (5.59%), along with smaller amounts of Carbon, Calcium, and Iron, confirming the dominance of hydrophilic clay minerals like illite, which directly account for the material’s pronounced swelling-shrinkage potential and high plasticity (liquid limit of 41.3%, plasticity index of 23.82). Finite element simulation under natural conditions powerfully corroborated these findings, identifying a distinct, deep-seated arc-shaped slip surface. The equivalent shear strain and horizontal displacement cloud maps clearly illustrated that the sliding mass was primarily concentrated in the middle and upper sections of the slope—the zone most susceptible to seasonal water-level fluctuations and repeated wet-dry cycles. This numerical result directly linked the microstructurally observed water sensitivity to the macroscopic failure mode, demonstrating that strength degradation due to moisture ingress in these zones is the dominant trigger for instability, even while the slope may retain a marginally high safety factor in a transient, natural state. [Conclusions] Poor gradation, hydrophilic mineral composition, and disordered, porous microstructure collectively engender high water sensitivity, significant swell-shrink potential, and low shear strength. A comprehensive treatment framework is proposed: 1) surface drainage and internal seepage guidance involving cutoff drains, drainage ditches, and blind pipes to actively control water infiltration and reduce pore pressures; 2) slope cutting and soil modification & reconstruction involving the removal of sliding mass and the replacement with cement-stabilized soil or other modified materials to enhance overall stability and create a protective cap; 3) anti-slide piles and rigid retaining structures to provide direct mechanical resistance against residual driving forces; and 4) slope anchoring and soil locking using soil nailing walls and tie-back systems to physically key the unstable sliding mass into the deeper, stable bedrock, thereby improving overall integrity and shear resistance.