Evaluating pedogenesis and soil Atterberg limits for inducing landslides in the Western Ghats, Idukki District of Kerala, South India

Abstract

In the Western Ghats of India, the soil properties, particularly Atterberg limits, are of relevance to the landslides. Pedogenic processes in the Western Ghats and plateaus on it are regulated by parent materials, relief (topography), organisms, climate, and time. In this study, the five major soils found within the mid-part of the Western Ghats in the Idukki district of Kerala, Southern India was analyzed for elucidating physical, chemical, and geotechnical properties (Atterberg limits) on landslides potentiality or slope failure processes. The result reveals that the highly weathered lateritic soils noted with lower KCl pH (3.6–4.6), low-cation exchange capacity (3.1 to 19.6 cmol( +) kg−1), low-effective cation exchange capacity (0.8 to 10.7 cmol( +) kg−1) and a negative ∆pH value indicate the presence of variable charge minerals such as amorphous sesquioxides. The variable ranking of random forest revealed that the soil Atterberg limits were significantly influenced by Citrate Bicarbonate Dithionite (CBD) iron, sand fractions, and organic carbon. The layer of porous sandy soils showed lower Atterberg limits due to accentuate with clay matter, whereas the illuvial layer (Bt) have noted as higher Atterberg limits that lead to potentially collapsing gullies or triggering mass movement during heavy rainfall followed by intensive runoff due to instability of soil mass within proxy of the steeply sloping surface. Soil geotechnical properties such as liquid limit, plastic limit, and plasticity index are the main characteristics that decide the slope stability and failure in various parts of the study area, whereas the soil profile morphometry has significantly associated with the occurrence of landslides with the plastic limit value between 28.01 and 40.48. It was noticed that the failed slopes have a higher value than stable slopes along with the hill-range topography, with soil particle sizes range of silt and clay (8.79 to 36.17 and 22.31 to 57.74%) with the measurement of liquid limit (40.05 to 68.4), plastic limit (24.2 to 43.94), and plasticity index (7.81 to 24.8). This indicates that the pedogenesis of the weathering profile of soils have significantly influenced the Atterberg limits that triggering slope failure or landslides along the gullies and weathered lateritic uplands.