Compositional analysis and phase relations of soil mass from the active landslides of Babai River watershed, Siwalik zone of Nepal

The present study focuses on the compositional analysis and phase relationship of soil mass and their role to trigger landslides in the Babai River watershed, Siwalik zone of Nepal. A total of 76 landslides are selected for sampling and further analysis among 769 active landslides from the total study area. For the classification of soil, the Unified Soil Classification System (USCS) is adopted by using both the sieve and hydrometer analysis. The centered log-ratio (clr) and mean component fraction of sand, silt, and clay are obtained from the compositional analysis by using R and CoDapac v.2.02.21 software. Correlation of phase relationships like moisture content, unit weight, specific gravity, void ratio, porosity, and degree of saturation of each soil samples are obtained. The results indicate that the degree of saturation is highly correlated with moisture content and void ratio but less correlated with the specific gravity and dry density. Furthermore, the highly correlated variables are checked by multiple regression analysis and the best-fitted regression equation was obtained from the phase relation. The centered log-ratio and mean log of silt/clay fraction indicate that silt and clay constituents in the soil are responsible for the landslide initiation in the study area.