Landslide geohazard assessment using the finite element method: a case study of PK-21 along the Djendel highway corridor, Algeria

The stability of natural and engineered slopes is significantly influenced by cutting and filling activities during road construction, which can lead to potential landslides. This study focuses on conducting a slope stability analysis using geotechnical data obtained from investigations and landslide analyses carried out at Km-21 of the Fourth Ring Road in Djendel, Algeria. The research examines the effects of excavating a section of residual clay, which triggered a landslide. To understand the underlying processes of this landslide, the physico-mechanical characteristics of the soils obtained from boreholes were analyzed. Laboratory test results, including grain size distribution, Atterberg limits, water content, shear strength, and compressibility, were meticulously examined. The findings revealed that the soils were fine-grained and heterogeneous, with moderate to high plasticity. It was observed that the upper soil layer (residual clay) exhibited lower shear strength parameters, with cohesion at 5 kPa and a friction angle of 23°, compared to the undisturbed formations beneath it, which had cohesion of 15 kPa and a friction angle of 25°. The stability analysis was performed using PLAXIS 2D, a software based on Finite Element Methods (FEM). The results indicated a significant impact of the excavation on slope stability. The factor of safety was 1.383 before excavation in dry conditions and dropped to 0.951, indicating that the upper layer is prone to instability after a portion of its total weight is excavated. This decrease in the factor of safety demonstrates the critical role of proper slope management and soil characterization in preventing landslides during construction activities.