The presence of desiccation cracks can affect rainfall-induced slope stability through both hydraulic and mechanical ways. Despite the valuable insights gained from physical tests in literature, there still lacks understanding how crack characteristics impact water flow dynamics and slope stability, especially considering the coexistence of vegetation. In this study, new analytical solutions were derived for calculating pore-water pressure and slope stability for an infinite unsaturated slope with cracks and vegetation. Both enhanced infiltration from water-filled cracks and water uptake by plant roots are considered. Using the newly developed solutions, two series of parametric analyses were carried out to improve understanding of the factors affecting crack water infiltration and hence the stability of vegetated slope. The calculated results show that slope failure at shallow depths is governed by the surface crack ratio, whereas deeper failures typically occur with greater crack depths. The surface crack ratio primarily influences the hydraulic response at shallow depths not exceeding 1.5 m, hence affecting the factor of safety for slip surfaces within the crack zone. Moreover, increasing the crack-to-root depth ratio from 0.5 to 1.5 results in a 25% reduction in suction at 1.5 m, threatening slope safety in deeper depth after 10-year rainfall.

This research investigates the stabilization of infinite slopes in the Lesser Himalayan region using nano-silica (NS), employing analytical, numerical, and experimental techniques. The findings demonstrate significant improvements in slope stability, including an 800.3% increase in soil cohesion, a 320% rise in the factor of safety (FOS), and a 75% reduction in pore water pressure. These enhancements ensure the stability and safety of slopes in vulnerable terrains. This study aligns with multiple United Nations' Sustainable Development Goals (SDGs): fostering resilient infrastructure and innovation (SDG 9), enhancing community safety (SDG 11), supporting climate adaptation strategies (SDG 13), conserving land resources (SDG 15), and promoting sustainable material use (SDG 12). By addressing environmental challenges and advancing sustainable geotechnical solutions, this work contributes significantly to global efforts towards resilience and sustainability.

An analytical model is derived for predicting the flow field and stability of an unsaturated infinite slope subjected to steady infiltration. The proposed model is novel because it accounts for the hydraulic anisotropy of unsaturated soil. The governing equation for steady-state seepage in an infinite slope is established in terms of matric suction under a constant surface flux boundary condition. On the basis of the available experimental findings on the hydraulic anisotropy behavior of unsaturated soils, the relative hydraulic conductivity for a soil under unsaturated conditions with respect to the soil at saturation is postulated to be a direction-independent scalar. This postulation simplifies the governing equation to a form that is directly solvable via the relative hydraulic conductivity and the saturated hydraulic conductivity tensor. To enable sophisticated applications, an exponential law and a power law that are well established in the unsaturated soil literature are used to relate the relative hydraulic conductivity to the matric suction and the effective degree of saturation, respectively. Closed-form solutions are derived for the matric suction, the flow net (potential function and stream function), and the effective degree of saturation. Analytical solutions are also derived for the soil unit weight and overburden stress. These solutions are incorporated into the unsaturated infinite slope stability formula constructed on a suction stress-based effective stress failure criterion. Hydraulic anisotropy has been shown to directly affect the flow field and the change in matric suction, which, in turn, drastically affects the slope safety factor against shallow landslides. This finding demonstrates that neglecting hydraulic anisotropy can cause a considerable overestimation of the safety factor, resulting in an unsafe slope stability prediction. The proposed model is useful for preliminary evaluation of the long-term stability of unsaturated slopes during wet periods and the antecedent slope conditions for shallow landslide initiation under transient infiltration.

The assumption of seepage parallel to an infinite slope is realistic and indeed typical of most hillslope failures, to which one-dimensional infinite slope analysis may be applied. In this study, however, the general case of an ideal infinite slope of homogeneous isotropic saturated granular soil affected by uniform steady seepage with a vertical upward component was considered. Stability analysis was carried out in view of i) Mohr-Coulomb shear failure, the main result being the preparation of a stability chart for an infinite slope acted upon throughout by seepage in an arbitrary direction; ii) hydraulic instability in the guise of hydraulic heave failure. This occurs when the seepage gradient, at which the upward seepage forces transmitted to the soil exceed the gravitational forces, is the critical hydraulic gradient , for which a simple, albeit general, equation was derived. Subsequent comparison of these two types of failure showed that Mohr-Coulomb failure precedes hydraulic heave failure, except in one particular case, i.e. horizontal ground and vertical upward flow, where the failures are simultaneous. The study also considered iii) the phenomenon of static liquefaction resulting from undrained monotonic shear of saturated contractive loose soils, which generates a build-up of excess pore-water pressure triangle u. This leads to a sudden substantial or total loss of shear strength, i.e. the phenomenon of static liquefaction which, in turn, can produce catastrophic failures,even in gentle slopes. Lastly, in relation to the above mentioned excess pore-water pressure , an equation that enables us to estimate its value was easily obtained.

Precipitation is one of the most important factors inducing shallow slope failures, and the shallow slope covering bedrocks is prone to instability after heavy rainfall. In one-dimensional (1D) seepage-deformation coupling issues, permeability coefficient and moisture vary with matric suction in unsaturated soil. Combining mass conservation, Darcy's law, and elastic theory, an analytical solution for coupled seepage-deformation in unsaturated soil slopes during rainfall infiltration is derived using the Fourier integral transformation method. The analytical solution can be applied to a 1D seepage problem in a soil slope with flux at the top and impervious bedrock in the base under heavy precipitation, and is conducive to study infiltration into the slope under rainfall conditions. To validate the accuracy of the proposed analytical solution in this study, it is compared with monitored pore-water pressure data from the Gufenping Landslide in the red-bed region located in Nanjiang, Sichuan, China. The compared result shows a good consistency between the analytical solution and the measured results, with a minor relative error. Investigation of the parameters demonstrates that the water-level rise is closely related to the coupling, which is influenced by precipitation duration, precipitation intensity, soil properties, and slope angle. The bottom boundary of the slope is considered to be impermeable in this study, which leads to rainfall accumulation at the base over time, and the coupled effect becomes more pronounced at the bottom boundary.