In Quebec, highways are mostly constructed on clayey deposits. Embankments constructed on such compressible soft soils are further subjected to slope stability issues and require an in-depth understanding of the failure mechanism in order to choose the right analysis method.

Different methods such as the limit equilibrium method (LEM) and the finite element method (FEM) are commonly used to calculate the safety factor (FS) as the primary design criteria. However, the latter is highly dependent on previous methods, approaches and assumptions.

2D slope stability analysis are widely used to solve geotechnical problems. However, application of 2D modeling sometimes forces the user to considerable simplification of the problem which impacts directly the safety factor. The main disadvantage in 2D analysis is that either the critical section must be defined, or in consequence several cross-sections must be analysed to provide a reasonable assessment of the 3D effect. Additionally, it is usually found that using a 2D analysis on slopes where 3D conditions prevail, will lead to an underestimation of the slope’s safety factor.

Moreover, highways are sometimes constructed on highly fluctuated areas where 3D calculations are necessary in order to take the complexity of geometry and subsurface geology under consideration.

This study compares the results of 2D and 3D analyses using Midas GTS-NX, Soilworks and GeoStudio-SLOPE/W. The construction of a new highway alongside autoroute 50 in Gatineau Quebec will be used as a case study. A large segment of the new highway will be simulated on the 3D model using the construction stage model. The results obtained will be discussed in a detailed fashion and then compared with chosen critical sections that were evaluated for the same segment using a 2D analysis. A technical comparative discussion regarding the design procedures as well as the reasonable equilibrium between safety and economy will follow.