Engineering Geological evaluation of the Krishna Bhir Landslide, Benighat Rorang, Dhading District, after the 2026 Rasuwa Flood

Abstract

The Krishna Bhir landslide, located along the Prithvi Highway in Dhading District, Nepal, represents a reactivated, complex slope failure that severed a critical national transportation corridor. This study presents field-based geological observations and structural assessment carried out around the landslide shortly after the 26 August 2026 Rasuwa flood. Results indicate that fluvial toe erosion by the Trishuli River, intensified by flood-induced sediment aggradation and subsequent channel migration, served as the principal triggering factor, removing basal confinement and destabilising the overlying slope mass. Multiple tension cracks were documented across the crown, flanks, and reactivated landslide body, with thicknesses of 2–5 m and separations of 15–35 cm, alongside uphill cracks of 25–30 cm separation and 1–2 m depth, confirming progressive retrogressive deformation. Structural evaluation of the existing retaining and gabion wall systems revealed cracking of 20–50 mm and downward displacement exceeding 30 cm, indicating that mitigation structures have exceeded their functional capacity. Lithological characterisation identified highly weathered, fractured slate and black slate interbedded with carbonate rock and quartz veins, substantially reducing rock-mass strength. A newly constructed road cut above the landslide crown, inclined at approximately 40°, further compromises stability within the weathered central zone despite relative competence in fresher rock.