Geological-Material Model Complexity Level and Excavation Sequencing on Numerical Modelling of Progressive Failure in Deep Open-Pit Slopes: A Case Study in a Porphyry Deposit Mine
Creators: Puerta Mejia, Andres F
Publisher: name: University of Alberta Library
Year: 2024

<p>This research delves into the intricate dynamics of progressive rock slope failure and its significant impact on the stability of deep open pit mining operations (over 500 meters according to Li et al., 2022), focusing on the crucial aspect of inter-ramp failure (large scale). The primary objective of this study is to comprehensively evaluate the implications of different levels of detail in Geological and Material models. Moreover, the research explores the intricate influence of various pushback sequencings (Excavation sequences) on the accurate modelling of progressive failure in deep open-pit slopes, thereby highlighting the depth of our study.</p>

<p>The research methodology employs a meticulous back analysis strategy to accurately replicate inter-ramp failure within a principal slope of a deep open pit mine. A series of geometrical pushback sequence models are systematically constructed, incorporating various levels of detail in Geological and Material models. This modelling spectrum ranges from simplified representations using homogeneous elastic materials to more intricate scenarios involving lithology differences, hydrothermal alterations, and Mohr-Coulomb with strain-softening materials, thereby instilling confidence in the thoroughness of our approach.</p>

<p>The modelling process commences with creating detailed geometrical models in Rhino V7.0 software, followed by a comprehensive analysis in Itasca&#39;s FLAC3D V.7.0 software. The evaluation of model results includes in-depth comparisons of displacement records, stress patterns, plastic strain, shear strain, and volumetric strains. This rigorous analytical approach aims to discern the subtle implications of increasing levels of detail in Geological and Material models on the forecasting accuracy of progressive failure.</p>

<p>Moreover, in the context of this case study, our research delves into the influence of different pushback sequences on the progression of failure. The results of this study underscore the significant impact of pushback sequencing choices on the initiation and extent of progressive slope failure, given the diverse stress paths within the slope. This comprehensive investigation significantly enhances our comprehension of the intricate interplay between excavation sequencing, stress paths, and slope stability, emphasising the importance of our findings.</p>

<p>According to the results of thorough model comparisons, there is a direct relationship between realistic depictions of progressive failure and the detailing levels of Geological and Material models. This relationship is created while critically considering various pushback sequences. Using fewer complex models allows for establishing restrictions for residual parameters related to strain-softening materials, expediting the iterative calibration process for more complicated models.</p>

<p>The study underscores the pivotal role of Geological-Material Model Complexity and Excavation Sequencing in projecting progressive failure in deep open-pit slopes. Through an in-depth analysis of a Porphyry Deposit Mine, novel insights emerge. Integrating geological complexities into numerical models is a crucial prerequisite for predicting progressive collapse. The most intricate geotechnical model, encompassing multiple lithologies, their alterations, and a strain-softening material behaviour model, is the most effective, accurately reproducing failure zone characteristics. Excavation sequencing significantly influences failure development, with different pushback sequences hastening or postponing failure initiation, thereby impacting the magnitude and spread. Pushback geometry, such as slope angle and spacing, is closely linked to failure initiation and progression. These findings provide unique perspectives on mitigating slope instability hazards in open-pit mining. Further research is needed to validate and generalise these findings across diverse geological contexts, considering additional factors such as large-scale fractures. </p>