Modified TOBIA Index: A GIS-based method for quantifying kinematic susceptibility along NH-7 in the Himalaya

Abstract The original form of Topographic/Bedding Plane Intersection Angle (TOBIA) index is limited to planar sliding only and lacks in determining kinematic feasibility for wedge failures. This study introduces a modified TOBIA index to overcome this major limitation of the original TOBIA index. The proposed modified method incorporates the plunge and trend of the intersection line between bedding plane and major discontinuity, providing a more comprehensive quantification for wedge sliding in computation of TOBIA index. The present study demonstrated the applicability of the modified approach along a road-section prone to structurally controlled landslides, including planar and wedge sliding. Structural orientation data were interpolated through geostatistical methods to create continuous layers of bedding dip amount, dip direction, and intersection line parameters. Both categorical and continuous TOBIA models were generated, and their outputs were compared and validated using weights of evidence (WoE) and rose diagram analyses. Results indicated that cataclinal slopes are highly susceptible to wedge, while orthoclinal slopes exhibit mixed behavior depending on local structural configurations and anaclinal slopes are comparatively stable, except few escarpments promoting toppling. By integrating both traditional and modified TOBIA indices, a unified kinematic susceptibility map of the studied section was generated, offering a robust tool for kinematic susceptibility assessment for planar and wedge sliding.