## 1 Introduction
[66], using a novel combination of in-site measurements and numeric simulations performed in MIDAS and FLAC codes, with each analytical step being calculated through the SSRM. The SSRM was further enhanced by incorporating a hierarchical multiscale approach developed by [PERSON] et al. [67], who introduced micromechanical parameters such as normal cohesion, tensile cohesion, and the angle of friction, to establish a new computational tool for heterogeneous geometrical slope stability analysis. An improved numerical manifold method [68] with multiple layers of mathematical cover systems [69] was proposed by [PERSON] et al., to analyze the stability of the soil-rock mixed slopes, by modifying Young's modulus and Poisson's ratio during the factor of safety (FoS) calculation using the SRM technique. This year, a technique called root bracketing was used by [PERSON] et al. [70] to enhance the SSRM's efficiency when performing slope stability analysis, allowing the minimization of the number iterations that need to be computed in order to determine the FoS. Several software products such as FLAC3D and 3 DEC [71; 72], Plaxis3D [73; 74], Phase2 and Slide [75; 76], or Comsol Multiphysics [77] use SSRM to compute the FoS for slopes of various geotechnical constructions such as dams, embankments, and waste dumps. Each software has its own strengths and weaknesses, so the choice of a particular software is based on the particularity of the problem that needs to be solved and the experience of the user. COMSOL is used by [PERSON] et al. [78] to determine the stability of a slope considering a coupled model subjected to thermal (temperature variation), hydraulic (water pressure), and mechanical (stress/displacement) processes, with the results being validated by three experimental and numerical case studies. In their study [79], [PERSON] et al. again used COMSOL to solve a coupled slope stability and hydrological model, for both single- and dual-permeability flows. The results obtained by the simulation were compared against two examples in order to validate the findings. An optimized version of the SSRM is proposed by [PERSON] et al. [80] to compute an embankment stability problem considering unconfined seepage. Matlab code was used to optimize the solution obtained using various [PERSON] approaches and the results were compared with the commercial Plaxis and COMSOL Multiphysics software's results. Another study conducted by [PERSON] et al. [81] validates the FoS obtained by an optimized variant of the shear strength reduction method in the case of three embankments with unconfined seepage, and they propose a comparison usingPlaxis and COMSOL between SSRM, modified SSRM, and optimized MSSRM on numerical examples representing a case study of a real heterogeneous slope. The stability analysis of rocks surrounding a natural underground natural gas storage has been performed by [PERSON] et al. [82] using the capabilities of COMSOL and Matlab, taking into consideration the effect of mechanical stress and low temperature. Based on its use for solving various stability problems as presented above, and considering the past experiences [83; 84] of the authorial team in using it, COMSOL Multiphysics software was chosen for the present study. The aim of this study is to evaluate the stability of waste dumps using different slope angles under both associative and non-associative plasticity models. To achieve this, a series of steps were taken: (i) A model was constructed based on real waste dumps from two lignite exploitations situated in the Motru coalfield, located in the Oltenia region of Romania. (ii) For that model, a stability analysis was conducted for various slope angles, considering geometric dimensions compatible to the real slopes, and geotechnical characteristics of the material from those waste dumps.