Author ORCID Identifier

https://orcid.org/0009-0006-6021-2672

Semester

Spring

Date of Graduation

2025

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mining Engineering

Committee Chair

Deniz Tuncay

Committee Co-Chair

Deniz Tuncay

Committee Member

Deniz Tuncay

Committee Member

Deniz Talan

Committee Member

Zach Agioutantis

Abstract

Underground stone mining accounts for approximately 21% of all underground mining operations in the United States, with more than 2,000 workers employed in this sector as of 2019. Ground control failures, particularly those involving massive pillar collapses and roof falls, pose significant safety hazards, contributing to 40% of fatalities and 15% of lost workdays since 2006. Several massive pillar collapses have occurred in active limestone mines from 2015 to 2021, and a fatal incident was reported in January 2022 in a mine operating within the Loyalhanna formation. Given these risks, accurate stability assessment tools are essential for improving mine safety.

The room-and-pillar mining method is predominantly used in underground stone mines, requiring careful design and monitoring of pillars throughout a mine's lifespan to mitigate ground control hazards. In the U.S., empirical pillar strength equations and the S-Pillar program were developed to assist in pillar stability design. While the S-Pillar software evaluates pillar stability by calculating the safety factor based on empirical equations, it assumes uniform overburden loading. It is only valid for regularly sized pillars, limiting its effectiveness for complex mine geometries and variable topographies.

LaModel, a displacement-discontinuity boundary element method software traditionally used in coal mining, has recently been applied to stress analysis in stone mines. This research aims to investigate LaModel's applicability further.

A case study of a benched pillar collapse incident is analyzed using LaModel, incorporating the effects of load transfer mechanisms and stress redistribution assessments under real-world mining conditions. Once the model is validated, parametric studies are conducted, including the width-to-height ratio difference, the collapse of a single pillar with stress propagation, lamination thickness, and width reduction due to spalling, to explore these parameters. In the case study of single pillar collapse, the results showed a stress transfer effect, with an average reduction of approximately 9% in the safety factor in adjacent pillars. This finding highlights the dependency of pillar stability, where the collapse of one pillar can compromise the structural stability of the surrounding pillars. The research also explored how varying lamination thickness affects stress distribution within materials. Results indicate that thinner laminations led to increased localized stress concentrations.

And increased the tendency of structural pillars to failure. On the other hand, a thicker lamination correlated with a more uniform distribution of stress, ultimately improving the overall stability of the structure. Additionally, a 10% and 20% reduction in pillar width due to spalling resulted in corresponding strength reductions of 3.1% and 6.48%. While a decrease in strength was observed, no significant increase in stress was found in the adjacent pillars, possibly due to the high elastic modulus of limestone. However, gradual spalling over time may lead to long-term weakening of the pillar system, making early detection and prevention crucial. Overall, the results show LaModel's applicability for stone mining and offer improved methodologies for pillar design.

The second phase of the study integrates mine map layouts with high-resolution Light Detection and Ranging (LIDAR) scans to improve pillar stability assessment. A combination of software tools, AutoCAD, AutoCAD ReCap Pro, CloudCompare, and Discontinuity Set Extractor (DSE), was utilized to process and analyze point cloud data. By overlaying 2D mine maps with 3D LIDAR models, the study quantified pillar width variations and conducted rock mass characterization using Rock Quality Designation (RQD), Rock Mass Rating (RMR), and the Geological Strength Index (GSI). A comparison between designed and actual pillar geometries revealed a 21.5% width reduction, which was incorporated into a revised LaModel simulation. The findings underscore the need to integrate empirical and numerical modeling approaches for a more comprehensive assessment of pillar stability.

By integrating empirical strength equations into numerical modeling software, this research aims to bridge that gap for underground stone mines, improving the reliability of pillar stability assessments. The enhanced stability mapping will offer a valuable resource for underground stone mine operators to identify potential hazard zones and mitigate the risks of catastrophic collapses.

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