Date of Award
Master of Science
This study has examined 3D stresses and displacements around a longwall mining system that is intercepted by a geological fault. More specifically, the study has analyzed the effect of a fault on longwall gate development entries, set-up rooms, T-junctions, and the longwall face as the longwall face progressed toward, through, and away from the fault. A general lithologic sequence and mining parameters related to the Herrin No. 6 coal seam in southern Illinois were employed. FLAC3D structural analysis code was used for simulating two (2) adjacent longwall faces. Linear elastic rock mass elements with non-linear elastic-plastic fault elements were analyzed using Hoek- Brown brittle failure criteria. Two (2) models were developed for analysis: a base elastic case without fault and an elastic model with elastic-plastic fault elements. Engineering properties for the rock mass strata were derived from a history of rock core testing and modified following the process indicated for Hoek’s Geologic Strength Index. Gob engineering properties and estimated load carrying capacities developed in earlier studies were used to make simulations physically realistic. The local tectonic (horizontal) stress field and vertical stress levels were applied to the simulation boundaries. Analysis data was extracted for several data lines in the roof and floor that were determined to be critical based on the geometry of the mine layout. Extracted data included 3D stresses and displacements with the Z-direction indicating vertical. This data was used to calculate vertical convergence and vertical and horizontal stress concentration variables VSCF, HSCF-XX, and HSCF-YY. Such data were developed for the longwall face advancing in 30-foot (10-m) increments away from the set-up room. Incremental displacements due to the fault proved to be more significant than changes in stress concentrations VSCF, HSCF-XX, and HSCF-YY. Set-up room X-displacements show a consistent increase in the fault case around 35%. Incremental Y-displacements vary sharply at first then changes quickly reduce to zero (0). Z-displacements were similar in both models. A fault oriented more vertically would have larger Z-displacement values. Gate X-displacements significantly decrease in the fault model until the face reaches 558 feet (170 m) from the starting point. Y-displacements show a rapid percentage rise in the fault model as the longwall face approaches the intersection of the fault with the first gate entry, but significant percentage decreases both before and after reaching this intersection. Significant increases in Z-displacements occur as the face approaches and leaves the intersection of the fault with the gate entries. Around the fault, the first row of gate pillars experiences a change in horizontal displacements HSCF-XX and HSCF-YY of approximately 10%. Second row pillars also see a change in HSCF-XX of around 10%, but not a significant change in HSCF-YY. Gate entry VSCF values show significant increases at the fault intersection until the face passes the gate/fault intersection.
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