The unified effective stress equation based on suction stress, a widely accepted method for calculating effective stress in unsaturated soils, provides a closed-form solution that enables the characterization of soils in both saturated and unsaturated states. The effect of desaturation on the water content of natural and treated soils was studied with respect to unconfined compressive strength (UCS) and indirect tensile strength (ITS). The soil's moisture-dependent behavior was characterized by the van Genuchten (Soil Sci Soc Am J 44:892-898, 1980. https://doi.org/10.2136/sssaj1980.03615995004400050002x) and Lu et al. (Water Resour Res, 2010. https://doi.org/10.1029/2009wr008646) models and implemented using the equation. Suction tests were conducted using the dew point and filter paper methods, alongside UCS and ITS tests, on silty clay soil and microsilica-treated soil with microsilica contents of 5%, 10%, and 15%. The equation was validated by comparing mean total stress (p) and mean effective stress (p ') to deviatoric stress (q) and analyzing the friction angle at different suction levels. It proved applicable to both natural and treated soils, with valid moisture content ranges of 4-17.5% and 6-20%, respectively. This study experimentally confirms the equation's effectiveness in characterizing the hydro-mechanical behavior of soils under varying moisture conditions.

At present, the widely used bishop stability analysis method does not consider the unsaturated effective stress, and the effective stress theory is unclear. To address these questions, this study initially explores a novel methodology for determining pore water pressure via the phreatic line. Subsequently, this study integrates the unified effective stress equation for both saturated and unsaturated soils, known for its clear physical significance, to propose an enhanced Bishop method(EBM) that accounts for effective stress in unsaturated soils. This EBM features a comprehensive theoretical framework, enabling direct stability analysis based on the phreatic line and demonstrating significant value for engineering applications. The reliability of the computational procedure of the EBM is validated through a saturated slope case study. Building upon this validation, the study further investigates the impact of incorporating unsaturated effective stress on slope stability. The results show that the deeper most dangerous sliding surface corresponds to an increase in the factor of safety(FOS) from 1.01% to 20.51% when considering the unsaturated effective stress. Overall, the integration of unsaturated effective stress exerts a positive influence on slope stability, underscoring the significance of this method for stability analysis and engineering design applications.