Engineering Geological Characteristics and Slope Stability of a Road-Cut Excavated in Serpentinite Mélange, Aceh Besar, Indonesia

Abstract

Road-cut slopes excavated in serpentinite mélange are highly susceptible to landslides because of the weak engineering properties of the rock mass, extensive weathering, and intense tectonic deformation. This study aims to investigate the engineering geological characteristics and slope stability of a road-cut excavated through serpentinite mélange in Aceh Besar, Indonesia. Field investigations were conducted to characterize the lithology, weathering conditions, rock mass quality, discontinuity characteristics, and evidence of slope instability. Geological observations were integrated with engineering geological assessments to identify the primary factors controlling slope failure. The investigated slope consists predominantly of highly weathered serpentinite mélange characterized by a heterogeneous rock mass, pervasive fracturing, and a weak serpentinitic matrix. The road excavation has significantly modified the natural slope geometry by increasing the slope angle and removing lateral support, thereby reducing slope stability. Field observations revealed loose rock fragments, localized erosion, detached blocks, and tension cracks, indicating progressive slope deterioration. Rainfall infiltration through discontinuities and weathered zones is interpreted as the principal triggering factor, whereas the weak lithology, advanced weathering, and abundant structural discontinuities constitute the primary predisposing factors. The dominant failure mechanisms are interpreted as rockfall and shallow translational sliding. The results demonstrate that serpentinite mélange represents a high-risk geological material for road construction in mountainous areas. Comprehensive engineering geological investigations, appropriate slope design, effective drainage systems, and stabilization measures are therefore essential to reduce landslide hazards and ensure the long-term stability of road infrastructure developed within serpentinite mélange terrains.