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UBC Theses and Dissertations

Comprehensive design methodology for coal mining under competent sandstone roof DuBois, Cale


This thesis presents a logical design methodology for coal mine extraction optimization under massive sandstone roof as developed though a case study analysis of the Quinsam Coal 4 South mine, a shallow underground room and pillar mine with a massive sandstone roof. This research is intended to guide Quinsam Coal and other coal mines globally in efforts to develop or optimize coal extraction and address the geomechanical challenges presented by massive sandstone roof. In this thesis, the tools required to facilitate effective site characterization, ground support design, excavation stability, pillar design, environmental risk management and mining method optimization are presented, as part of a comprehensive design methodology. Guidelines for pillar design are presented based on software assisted gravity-wedge analysis, and review of empirical and analytical design methods. Tools for addressing temporal change in pillar size, shape and stress as well as pillar jointing effects are provided. Pillars are designed to accommodate stresses and strains arising from the known range of overburden depths. An optimized non-caving checkerboard partial pillar extraction method is presented to mitigate environmental risk, address the poor and unpredictable caving mechanics of the massive sandstone roof and provide adequate coal extraction. Modeling of in-line pillar mining and checkerboard partial pillar mining methods was completed with ExamineTAB, a pseudo-3D displacement discontinuity program in support of checkerboard partial pillar mining. Instructional training is required with any modification in mining methods or conditions to apprise the underground workforce on the technical details of the mine design and the importance of adhering to the standards thereof. Using this research work and analysis of the 4 South mine as a backdrop, the design of coal mines under massive sandstone roof is facilitated. The application of the design methodology to the 4 South mine illustrated serves as a 'terms of reference' document for other professionals addressing similar geotechnical and environmental challenges to design safe coal pillar extraction under a massive sandstone roof.

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