An indication of the complete stress-strain behavior of coal was obtained through instrumenting a headgate yield pillar and monitoring the changes in vertical and horizontal pillar stress, pillar strain, and roof-floor convergence as a function of time and distance from the moving longwall face. A semiautomated monitoring program was conducted over a 5-month period as the longwall face advanced toward and eventually passed the instrumented pillar. The development of a confined core and yield zone within the pillar was confirmed by the vertical and horizontal stress changes. The in situ prefailure (208 to 661 mpa) and postfailure moduli (55 to 208 mpa) of the coal were determined from the change in pillar stress versus pillar strain. The in situ moduli are an order of magnitude lower than the 3,450 mpa commonly assumed for coal.
Int. J. Min. and Geol. Eng., V. 7, 1989, PP. 163-170
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