Interpreting the formation mechanism of a complex landslide: a case study of a reactivated landslide of a reinforced embankment slope

In the present work, geological and geotechnical studies were carried out to find the causes and mechanisms of a reinforced embankment slope failure. The information collected from the surface investigations combined with the borehole data analysis helped to understand the landslide process, to perform analyses to determine the movement mechanism, and to identify the factors contributing to the landslide. Subsurface features, including the sliding mass, slid surface, stable layer below slid surface, and groundwater, are determined based on borehole logs, from which cores of landslide masses and bedrock have been retrieved and analyzed. Laboratory tests were carried out to estimate the geomechanical properties of soil, sandstone, and mudstone that constitute the slope. Slope stability analyses were carried out to evaluate the effectiveness of the reinforcement system and to analyze the failure mechanism. A discussion is presented on the following aspects: (a) influencing factors and failure mechanism and (b) synergistic effect of rainfall and weak layer. The results show that the rainfall is the main inducing factor of slope instability, while the effect of the groundwater on the weak layer played a vital role in the landslide event. The anti-slide pile structure was found to be damaged, which indicates that further research is required in coming up with better designs and constructions of such structures for high fill slopes with soft foundations. The results also indicated that an effective drainage system should be implemented in improving the stability of the slope.