The application of 3D finite element method in the analysis of slopes under external loads

The majority of slope stability assessments in geotechnical engineering practice are typically carried out using two-dimensional plane strain analyses. However, there are instances where the results from 2D plane strain and 3D analyses can significantly differ. One such scenario arises when a slope is subjected to concentrated external surcharges, such as those exerted by cranes, piling rigs, and other construction equipment. A common practice is to convert these concentrated surcharges into equivalent infinite strip loads for analysis in a 2D plane strain context. While historically regarded as a conservative approach, the suitability of this conservatism can be questioned from a design standpoint. This paper presents a comprehensive parametric study comparing 2D and 3D slope stability analyses, focusing on factors such as surcharge loading magnitude, configuration (dimension and offset), slope angle, and width of the slope mechanism. The analyses utilise the elastoplastic finite element method employing the strength reduction technique. Comparisons are made in terms of safety factors, shear failure mechanisms, and deformation behaviour. The results underscore the significance of employing 3D FEM analysis for slopes experiencing highly concentrated surcharge loads, particularly those associated with crane lifting operations. Furthermore, it was demonstrated that in scenarios involving such concentrated loads, stress distributions and potential failure mechanisms could be complex and are better evaluated within a 3D FEM framework. This approach leads to an optimised design solution without compromising safety, especially in construction operations adjacent to existing slopes.