Geotechnical Instabilities in Road Embankments: Analysis of a Landslide in Schistose Road Cut-and-Fill on the Taza-Al Hoceima Expressway, Northern Morocco

This article delves into the vital issue of geotechnical stability in road embankments, a crucial element for the integrity of road infrastructures and the safety of its users. It focuses on a specific case of landslide along the Taza-Al-Hoceima highway at kilometer point 67+800. This case is particularly significant due to the embankment's composition, which predominantly consists of schistose cut and fill, in addition to the topographic and hydrographic complexity of the area. The main ambition of this study is to delineate the various factors and underlying mechanisms that precipitate such geotechnical instabilities. To this end, the research integrates field investigations with laboratory analyses. A major aspect of this research involves examining the characteristics of the schists at the site. These schists are identified as fragmentable clayey rocks (R34), demonstrating a range of Micro-Deval (MDE) coefficients between 67 to 100 and Los Angeles (LA) coefficients from 33 to 57. Upon alteration, these schists are reclassified as fine soils (A2), consisting of 35-40% fine particulate matter, with plasticity indices ranging from 13 to 22 and a high permeability rate (Kp=10-3 m/s). The study underscores the schists' vulnerability, particularly their susceptibility to evolutionary changes and water sensitivity. It also reveals that local geomorphological and hydrodynamic conditions exacerbate water infiltration. Heavy rainfall is pinpointed as the trigger for the landslide incident. Although the current road drainage system effectively manages surface water, the findings of the analysis emphasize the critical need to enhance this system to address the significant water infiltration problem identified.