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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.

Coarse-grained soils are a type of soil frequently found in civil engineering projects, and their mechanical characterization still presents a real challenge. They are composed by elements of different dimensions (from a few microns to tens of centimeters), and can be of very varied nature (clay, sand, gravel, pebbles, etc.). The mechanical characterization of coarse-grained soils is very difficult because of the presence of large elements. In order to be able to characterize them in the laboratory by means of conventional size devices, it is very important to study the influence of significant parameters on the mechanical behavior of coarse-grained soils (the volume fraction, particle size distribution and spread, consolidation level and initial state of the matrix), using the large-sized triaxial testing device. In this paper, we will propose a methodology for evaluating the mechanical characteristics of coarse-grained soils based on soil granulometric reconstruction procedures. The method we have named GALA is based on the use of polynomial correlations between the strength increase due to inclusions and the volume fraction fv and the particle spread (d min /d max) of inclusions. We were able to apply this new method to a natural soil. The results showed the relevance of our method.

Coarse-grained soils are a type of soil frequently found in civil engineering projects. The mechanical characterization of these soils is very difficult because of the presence of large-sized elements that disturb or prevent the realization of the tests. However, there is still no rational procedure to characterize coarse soils and determine their mechanical characteristics (cohesion and friction angle) for the calculation of slope stability or structures. The objectives of the research work are to contribute to the improvement of the knowledge of the mechanical behavior of matrix coarse-grained soils and to propose a rational procedure to characterize them. In order to achieve these objectives, it is important to understand the influence of the fundamental parameters related to the mode of reconstitution on the mechanical behavior of the coarse soils: volume fraction, particle size distribution and spread, consolidation level, and the initial state of the matrix. Tests are carried out using the large-sized triaxial testing device in drained conditions. With natural coarse-grained soils, it is very difficult to conduct repeatability tests to validate the results. For this reason, we will study a particular category of coarse-grained soils composed of inclusions (coarse elements) within a fine sandy matrix (matrix coarse-grained soils), using a reference soil composed of a mix of sand and gravel. The results show that for both states of sand compaction (ID=0.4 and ID = 0.8), the shear strength of the soil increases with the increase in the proportion of gravel. This increase is more marked in the case of uniform 8/10 mm gravel. Thus, the size of inclusions has no significant influence on the value of qmax. Doi: 10.28991/CEJ-2022-08-08-012 Full Text: PDF