Integrated Engineering Geological and Geotechnical Assessment, Slope Stability Analysis at the Nigalo Boutique Resort Landslide, Nagarkot, Nepal

Abstract

Rainfall-induced slope instability at Nigalo Boutique Resort, Nagarkot, was investigated following a landslide triggered by approximately 16 hours of continuous heavy rainfall on Ashad 22, 2081. The study integrates engineering-geological mapping, topographic surveying, geotechnical investigation, infiltration testing, laboratory analysis, borehole data, and limit-equilibrium slope-stability analysis to characterize the unstable slope and assess mitigation measures. The investigation covered approximately 11,000 m² and included total-station surveying, field-density and portable DCPT testing, infiltration measurements, geological mapping, grain-size analysis, moisture content, specific gravity, Atterberg limits, and direct-shear testing. The slope comprises gneissic bedrock overlain by variable colluvium and silty soil, with springs, erosional gullies, cracks, a roadside canal, and damaged retaining structures contributing to instability. Laboratory results indicate moisture contents of 13.37–56.97%, specific gravity of 2.60–2.68, cohesion of 4.58–9.03 kPa, and friction angles of 21.69°–27.14°, with an average infiltration rate of 0.0002 cm/s. Morgenstern–Price analysis in GeoStudio 2D yielded FOS values of 1.025 under dry conditions, 1.012 under probable groundwater conditions, and 0.472 under seismic loading. The proposed combined reinforcement/nailing and reinforced-soil-wall system increases the FOS to approximately 1.9, demonstrating improved stability and emphasizing the need for integrated structural reinforcement, drainage, erosion control, and long-term monitoring.