Retreat mining is a mining method typical to underground room and pillar mines. The process of retreat mining inherently creates an unstable environment as pillars, which are initially left in place to provide support for the mine, are removed. As a result, retreat mining is associated with high risk, safety concerns, and ground control issues. Safety is a critical concern in the mining industry to ensure all workers make it home, safe, every day. As a result, it is important to conduct research to advance the understanding of the mechanics associated with retreat mining and improve the safety of the method.
Previous research regarding to retreat mining in room and pillar mines is limited. Research has mainly focused on modeling individual components of retreat mining (i.e. roof/floor influence, gob development, retreat method). Research has resulted in the overall progression of modern-day pillar mechanics and design, which has resulted in improvement in the design of mines employing retreat operations. However, there is a relative lack of research on investigating the retreat phase of room and pillar mining and how the entire retreat process impacts the global and local stresses in the mine. This thesis aims to contribute to closing this gap.
A preliminary study was performed in order to understand the influences of model type (elastic versus inelastic), pillar width to height (W/H) ratio, and roof properties on the overall retreat mining process. The aim of the study was to constrain how parameters influence stress redistribution during the retreat mining process through the use of numerical modeling. It was found that inelastic numerical models were able to capture the yield propagation within a pillar array that allows for potential investigation of pillar failure. The W/H pillar ratio and roof properties were seen to influence stress redistribution through the various modeling attempts.
In addition, further investigations on the impacts of retreat mining on global and local scale stress transfer and damage were performed. This was done through the development of a numerical model of Mine C, a room and pillar coal mine in the Western U.S., and the calibration of the numerical model to field data. A calibrated model was established and was found to be in good agreement with the field data. Throughout the retreat process, stress redistribution and yield was most prominent in the pillars near the active mining area. The minimal changes in stress and yield in pillars outside of the active mining area suggest an adequate mine design that was able to isolate the impacts of retreat mining to within the active mining area.
The resulting calibrated model provides a unique opportunity to investigate various components that are unique to retreat operations, such as depillaring sequence, mine design, and support influence. The developed numerical model can be used for future research focused on rock mechanics and ground control in the context of retreat mining.
Copyright of the original work is retained by the author.
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