Slope Stability Analysis in bimsoils

This thesis is devoted to the stability analysis of a slope in a rock mass characterized by a Block In Matrix structure (BIMsoils). The complex mechanical behaviour of these materials has been widely studied and some characteristics have been found to affect deeply the failure process in unstable slopes: the volumetric block proportion (VBP) of blocks, the block size distribution and the position of the blocks inside the slope. All these characteristics have been analysed in this work, by means of numerical analyses by FEM, implemented in RS2 code, of a simple slope. Four different VBP (25%, 40%, 55% and 70%) were analysed. The bimsoil slope models have been built according to the stochastic procedure suggested by Napoli et al. in 2021, and interfaces elements, characterized by cohesion, internal friction angle and tensile strength, have been added at the contact between the blocks and the matrix. The strength parameters of the block- matrix interfaces were then reduced to 50% and 100% in order to take into account different heterogeneous geomaterials with variable block-matrix adhesion characteristics. The results were compared to those obtained by Napoli et al., 2021. The results of the numerical analyses were illustrated in terms of safety factors. For further validation of the models, a simulation by taking the mechanical properties of the block- matrix interfaces equal to that of the matrix was also performed. At the final stage of the study the tortuous failure surfaces developed for all the VBP considered were drawn using AUTOCAD and analysed. It was observed that when the cohesion and the tensile strength of the block-matrix interfaces were 50% reduced with respect to the strength properties of the matrix the average safety factors of the bimsoils were slightly higher for 25% and 40% VBP but there was a slight decrement in the average safety factor for the higher VBPs (55%,70%). When the cohesion and the tensile strength of the block-matrix interfaces were 100% reduced, a very small variation of the average factor of safety for 25% and 40% VBPs was observed, while a significant decrease in the average safety factors could be noted for the higher VBPs (55%, 70%) (Napoli et al, 2018). Another important observation is that the location and shape of the failure surfaces in the slopes do not coincide with that expected in an homogeneous material. This result was achieved for all the considered VBPs (25%, 40%, 55%, and 70%) but with different shapes and lengths. In particular, the tortuosity of the failure surface has been observed to increase as VBP increases and the cohesion of the block-matrix interfaces decreases. The results obtained confirm what was highlighted by previous research (Napoli et al, 2021): it is not realistic to model the problem by assuming the bimrock as an equivalent homogeneous material, because the real shape and position of the failure surface can not be correctly estimated, with consequent mistakes in the evaluation of the slope stability condition.