Integrating unsaturated soil mechanics for sustainable landslide mitigation strategies

Rain-induced landslides and slope instability pose significant threats in mountainous regions with deep water tables, including the hilly tracts of Bangladesh, where unique geological compositions and soil properties exacerbate these risks. This study offers a comprehensive characterization of unsaturated soils, focusing on laboratory measurements such as the soil–water characteristic curve (SWCC), permeability (k) function, saturated permeability (k_sat), and suction-monitored direct shear tests, with particular emphasis on low plastic silty clay (CL-ML) soil types. The implementation of a multilayer covering system (MLCS) with a capillary barrier system to prevent precipitation infiltration into residual soil slopes demonstrates the application of unsaturated soil mechanics theories. Moreover, the study investigates the role of vegetation, specifically live stakes, in reinforcing slope stability. Laboratory and numerical analyses of a typical slope in the Chittagong Hills region reveal that the factor of safety (FS) against slope failure with the deployment of MLCS reaches 1.25 following 72-h rainfall events with an intensity of 1.2 × 10⁻⁶ m/s (106 mm/day), whereas the FS for the natural slope falls below 1.0. This research yields valuable insights into regional soil properties and presents sustainable solutions that integrate engineering and bioengineering concepts to effectively mitigate rain-induced slope failures in mountainous areas.