Conventional strata control methods (i.e., roof bolts, cable trusses) are not always effective for ground control of very weak coal strata. An alternative method, termed presupport, is being investigated by the U.S. Bureau of Mines. In this paper structural modeling of presupport concepts and field testing of a presupport application are presented. Finite-element models indicate that forepoles significantly lower beam stresses in the roof strata overlying a coal seam, but they cannot be expected to prevent or reduce roof strata failure at the coal face due to the presence of a high stress concentration at that location. However, their presence near the coal face is needed to sustain the fall of roof if it does occur. Because of an ever-present severe stress concentration at the coal face, it would appear that stresses could exceed material strengths, causing local structural damage, especially if the rock is very weak. Therefore previous coal face positions along an entry may have a higher-than-normal probability of roof fall. In the field investigation, a low-cost air injection test has thus far shown promise as a tool for evaluating the effects of forepoling on the roof strata. Observations of coal mine entries in which forepoles have been installed indicate forepoling is effective in controlling very weak roof strata.
Proc. 9th Int'l Conf. on Ground Control in Mining, WVU, Dep. Min. Eng., 1990, PP. 42-51