SBAS InSAR, UAV, and Numerical Modeling of Slope Instability in Tbilisi, Georgia

The Vere River basin in Tbilisi, Georgia, experienced a major cascading landslide–flood disaster in June 2015, emphasizing the need to evaluate the present stability of slopes adjacent to the former source area. This study combines small-baseline InSAR (SBAS), RTK-UAV photogrammetry, COSI-Corr image correlation and LS-RAPID numerical modeling to investigate whether the slope remains active and how it responds to changing pore-pressure conditions. Analysis of 109 ascending Sentinel-1 acquisitions acquired between April 2022 and October 2025 revealed persistent positive line-of-sight deformation across the investigated slope. Independent UAV/COSI-Corr analysis identified horizontal displacements of approximately 0.05–0.09 m over 149 days, exceeding the empirical relative displacement detection threshold of 0.0235 m. The measured displacement direction broadly follows the downslope and structural orientation, although its angular offset suggests that the movement is influenced by a combination of topography, bedding, fractures, and heterogeneous slope materials rather than a single planar control. LS-RAPID simulations further showed a nonlinear response to increasing prescribed pore-pressure ratio. Together, the observations indicate that the slope has not fully stabilized after the 2015 event and continues to undergo slow deformation while remaining sensitive to hydrological conditions. This is particularly important for Tbilisi because renewed slope instability in the Vere valley could interact with the confined river corridor and urban infrastructure, increasing the potential for cascading impacts.