Integrated Large Discontinuity Factor, Lamodel and Stability Mapping Approach for Stone Mine Pillar Stability

Abstract

The objective of this research is to develop a software tool that integrates the large discontinuity factor (LDF) and the Boundary Element Method software (BEM), LaModel, to allow stone mine operators to assess the impact of the large discontinuities on local pillar stability. National Institute for Occupational Safety and Health (NIOSH) published design guidelines for underground stone mines to guide the industry in designing pillar and roof support. These guidelines emphasize the impact of large, angular discontinuities on pillar strength. Esterhuizen et al. (2011) derived the large discontinuity factor (LDF) to account for the impact of discontinuities on pillar stability by adjusting the strength of the pillars. In this approach, the pillar load is calculated at the maximum depth over the pillar layout, and the tributary area loading calculation is valid if the mine layout consists of regular-sized pillars. Escobar (2021) extended the application of this approach to the BEM to allow stone mine operators to integrate overburden stress distribution under variable topography and pillar layouts with irregularly sized pillars into their designs. The software tool developed in this thesis incorporates the large discontinuity impacts, overburden stress distribution under variable topography, and irregular pillar layouts by utilizing: LDF, AutoCAD ObjectARX add-in Integrated Stability Mapping Software (ISMS), and LaModel software. In this research, a new term, Local Large Discontinuity Factor (LLDF), is proposed to explicitly account for the impact of large discontinuities on local pillar stability. The ISMS step transformation function is used to identify the pillars intersected by the large discontinuities and to generate the LLDF grid of the intersected pillars. LaModel is used to compute the safety factor of the stone mine pillars by simulating the strength of complex pillar geometries with the empirical stone mine pillar equation (Esterhuizen et al., 2011; Escobar, 2021). The software tool uses the LLDF grid and LaModel output files to generate the final pillar stress safety factors, which can be visualized in AutoCAD. After the development of the software tool, a case study was performed to demonstrate the application and usefulness of this new engineering tool.