The farther away from the startup room, the lower the applied load and smaller the con- vergence in the entry if all else is held constant. The results of this study showed that the rear abutment stress experienced by this bleeder entry design was minimal. The Flac3D model showed very good correlation between expected gateroad loading during panel extraction and that expected based on previous studies. The model showed a much greater increase in stress due to the development of the gateroad and bleeder entries, with about 80% of the increase associated with development and 20% with longwall extraction. The results indicated only a minor increase in load during the extraction of the longwall panel. The Flac3D program was used to evaluate these four bleeder entries using previously defined mod- eling and input parameter estimation procedures. As expected, the instrumentation of the standing supports showed very little loading relative to the capacity of the standing supports-less than 23 Mg load and 2.54 cm conver- gence. The primary focus was on the extent and magnitude of the abutment loading expe- rienced by the standing support. This paper details observations made by NIOSH researchers in the bleeder entries of a deep cover longwall panel-specifically data collected from instrumented pumpable cribs, observations of the conditions of the entries, and numerical modeling of the bleeder entries during longwall extraction. Several questions have emerged in relation to deep cover bleeder entry performance and support loading: how well do current modeling procedures calculate the rear abutment extent and loading? Does an improved understanding of the rear abutment extent warrant a change in standing support in bleeder entries? To help answer these questions and to determine the current utilization of standing support in bleeder entries, four bleeder entries at varying distances from the startup room were instrumented, observed, and numerically modeled.

Flac3d mac