Longwall mining is growing rapidly in Illinois. A coal company was faced with crossing a 3-m normal fault in the development entries and the longwall face while mining a 375-m wide longwall face. Limited geologic and geotechnical data were available related to the fault. There were significant concerns about additional spatial displacements along the fault plane as the face approached and crossed the fault zone. These displacements could result in additional loading on the development entries on the headgate and tailgate sides as well as in the face area that could affect ground control performance in the face area. Field monitoring, observational and numerical modeling studies were performed to develop data that would assist the company to plan for additional supports in the development entries and take appropriate safety measures while advancing toward the fault and crossing it. Numerical modeling consisted of analyzing a 3-D structural model using the FLAC3D with the fault plane incorporated as ubiquitous joint. This model was used to analyze incremental displacements and stresses due to the deformations of the fault plane as the face advanced and crossed it. Additional stiff supports were installed in headgate entries around the stage loader and 60-m outby of the longwall face (solid).

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