Analysis and assessment of slope instability along international mountainous road in North Africa

The sliding incidences along the mountainous roads in the northern part of Algeria are considered a major hazard, often with huge impacts on infrastructures, causing terrible damages and significant economic losses. The present study reveals that the sliding incidences along N27 highway mountainous road in northeastern Algeria occur mainly in the clay layer that is found immediately below the water table. Slope deformation usually happens after several drying-wetting cycles which result in many vertical cracks at the slope crest. These vertical cracks are considered as the locations of slope sliding and control the characteristics of the sliding surface. During rainy seasons, the increasing weight of saturated upper slope soils creates enough pore water pressure to reduce the matric suction of slope geomaterials, tending to weaken and soften the slope soils and rocks. The results reveal that the cohesion of slope geomaterials is considered as the main shear strength factor, while the internal friction angle is non-significant in the instability of the N27 international mountainous road slopes. The seismic activity is a crucial trigger factor in slope instability, and the results prove the fact that the reduction percentage in the static factor of safety is ranging from 14.64 to 47.39% with an average of about 24.95%. The numerical finite element analysis results show that the sheet pile treatment method is an ineffective stability method at Oum Tourba and Chigara areas, while it could be a successful stability method at Grarem area. In this present study and based on the results of 2D limit equilibrium analysis and 2D numerical finite element analysis, it could be concluded that a combination of two or more possible suggested stabilizing methods, as per requirements, can be utilized to stabilize the N27 international mountainous road slopes. The selected definitive stability methods should be implemented simultaneously. If these stability methods are done jointly, huge damages and irremediable losses could occur along the N27 international road slopes.