Determination of slip plane geometry and classification of landslides on gentle slopes: Implications for management of degraded lands

Abstract

Shallow translational landslides on gentle slopes (~15°) in Herlang Subdistrict, Bulukumba Regency, South Sulawesi, have caused significant land degradation through soil erosion, nutrient loss, and damage to residential and agricultural areas in the weathered Walanae Formation. This study integrated 2D electrical resistivity imaging using the Wenner–Schlumberger array, Atterberg Limits testing, and Chemical Index of Alteration (CIA) analysis to elucidate landslide mechanisms and provide practical guidance for restoring degraded lands. The resistivity results indicated a saturated calcareous sandstone layer with very low resistivity (<7.53 ?m) as the main sliding mass, overlying a more competent fine tuff layer (28.9-111 ?m) at depths of 3.5-14.5 m, which serves as the slip plane. Soil samples are classified as high-plasticity clay (CH) according to the Unified Soil Classification System, with Plasticity Index values ranging from 34.55% to 39.82%. High CIA values (83.64-87.48) indicate intense chemical weathering leading to kaolinite dominance, which explains the marked reduction in shear strength upon saturation and the occurrence of translational failures even on gentle slopes. These integrated findings provide a robust scientific basis for developing low-cost restoration strategies, including subsurface drainage, terracing, and bio-engineering with deep-rooted vegetation, to enhance slope stability and restore soil function in similar tropical degraded landscapes.

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