Engineering Geology 281 (2021) 105968 Available online 16 December 2020 0013-7952/© 2020 Elsevier B.V. All rights reserved. Insights and perspectives into the limit equilibrium method from 2D and 3D analyses Bekir Salih Firincioglu a , Murat Ercanoglu b, * a Civil Engineering Department, Cyprus International University, Mersin 10, Nicosia, Turkey b Geological Engineering Department, Hacettepe University, Beytepe/Ankara 06800, Turkey A R T I C L E INFO Keywords: Limit equilibrium method 2D analyses 3D analyses Scenario-based analyses Slope stability ABSTRACT Stability analyses of slopes have been a hot topic for several decades and numerous methodologies have been introduced since the beginning of these analyses. One of these methodologies is the limit equilibrium theory, and it has been applied in different forms to various cases for almost a hundred years. Although numerous in- vestigations and works have been carried out on this methodology, there are still wide gaps needed to be investigated. Various methods have been introduced through the years including two- and three-dimensional solutions to the slope stability. However, an extensive investigation on the effects of real-life scenarios is still absent in the literature. Therefore, this study was aimed at modelling and evaluating the slope stability considering different scenarios in two (2D) and three dimensions (3D). Available methods have been investigated in both 2D and 3D separately by considering well known cases in the literature. Also, a comparison has been conducted between two- and three-dimensional versions of the same methods. Five different hypothetical cases and a multitude of scenarios representing the possible conditional changes on the slopes were investigated during the analyses. Thus, three distinctive comparisons have been conducted by analyzing 942 data related to the factor of safety. Many intriguing results have been discovered throughout the analyses and some of them have been found against the literature. A considerable amount of the computations has produced lower factors of safety in three-dimensional models. This outcome is arguably the most signifcant fnding of this study. 1. Introduction Natural or engineered slopes such as highway slopes and open-pit mines, or any inclined natural earth surfaces could be prone to fail if the suitable conditions are met. Prevention of such failures is vital for preserving human-life and of great importance in terms of economic losses for large scale projects in addition to the loss of properties. Hence, investigation of this problematic subject with the appropriate type of stability analyses is one of the most important stages of any engineering work. In the last century, many scientists and engineers have aimed to gain new perspectives for slope stability problems by developing new the- ories under various names. Some of these methods were based on satisfying static equilibrium, compatibility and boundary conditions such as Limit Equilibrium Method (LEM) and Limit Analysis Method (LAM), and some were based on the principles of continuum mechanics such as Finite Element Method (FEM), Boundary Element Method (BEM), Finite Difference Method (FDM), and others were derived from discontinuum mechanics as Discrete Element Method (DEM), Discon- tinuous Deformation Analysis (DDA) and Particle Flow Code (PFC). Moreover, some hybrid methods have been developed to compensate the disadvantages of each theory such as Discrete Finite Element Method (DFEM) and Finite Discrete Element Method (FDEM). All of these above- mentioned methods have pros and cons, therefore, they should be used cautiously by considering all the limitations and capabilities of each theory. However, the limit equilibrium method has been around for almost a hundred years, and it is still one of the most commonly used methodologies throughout the world. Slope stability analyses can be performed in both two and three di- mensions by simply drawing the cross-sections or creating sophisticated three dimensional models of the related structures. Stability analyses by limit equilibrium methods generally have been done by considering plane strain assumption which yields a two dimensional factor of safety for the problem considered; but in reality, failures of engineering de- signs such as embankments, vertical cuts, retaining walls and as well as natural slopes occur in three dimensions. The signifcance of this * Corresponding author. E-mail address: murate@hacettepe.edu.tr (M. Ercanoglu). Contents lists available at ScienceDirect Engineering Geology journal homepage: www.elsevier.com/locate/enggeo https://doi.org/10.1016/j.enggeo.2020.105968 Received 5 December 2019; Received in revised form 10 December 2020; Accepted 10 December 2020