Comparison of analytical and numerical methods in the analysis of the stability of an excavation of the high-speed line in northern Morocco

Abstract

The deformation and failure mechanisms on slopes and in particular the excavations, are very complex. Slope stability analysis is performed using two types of methods: analytical and numerical, which are compared in this article to evaluate their efficiency. The excavation object of this study is situated on the high-speed line between Kenitra and Tangier, specifically in the rural commune of Hjar Nhal, Tangier-Tetouan-Al Hoceima region. It extends for a 1170 m length, its maximum height is 62 m at the axis. The soil of the site is characterized by pelitic formations with the existence of numerous water sources at the base of the excavation. Modelling by analytical methods showed that the excavation did not present a stability problem, contrary to numerical modelling. Firstly, the analysis of the results shows that before the failure, the soil is continuous and that its behaviour cannot be analysed by analytical methods, because a fracture surface cannot be established. It is then necessary to consider numerical methods that take into account the entire volume to analyze the movements and their evolution over time. Secondly, hypotheses have been made about the possibility of a poor estimation of the mechanical characteristics of the soils that constitute the excavation. The review of geotechnical investigations has shown that these soils are coarse with discontinuities that favour water infiltration, and are difficult to characterize, which can lead to an overestimation of their mechanical characteristics.