Laserfiche WebLink
• 1.7 ZONES ALONG OUTCROP BARRIER PILLAR <br />The Bowie #2 Mine is limited by the both seam's outcrop on the south and east <br />sides. An outcrop barrier pillar will be left between the mined areas and the coal outcrop. <br />The width of such a pillar as well as its properties are important for the assessment of the <br />stability of the slope above it and for the assessment of the subsidence potential close to <br />this pillar. The limited overburden height, weathered rocks close to the surface and the <br />potential of the coal burn line extending into or close to the workings may contribute to the <br />subsidence potential in this area. <br />The important factors and conditions that may influence the stability of the outcrop <br />barrier pillar are fairly well defined. The coal outcrop is well defined; it is further known that <br />at most locations along the outcrop, both seams are burnt out. At some locations, such <br />as the Bowie #2 Mine portal entries, little coal burn was present. The depth of the coal <br />burn in the horizontal direction is much less defined; we understand that based on the <br />mining experience in the area, the width of the burnt-out zone has been assumed to reach <br />up to 300 feet. According to this assumption, the projected burn line, which coincides with <br />the southern mine limit, was estimated. <br />• Mining limits in areas adjoining the outcrop barrier pillar are usually dictated by the <br />occurrence of oxidized (weathered) coal close to the outcrop. Such coal is of lower quality <br />and weaker than the good quality coal and it is not mined. <br />The presence of the burnt-out coal close to its outcrop brings about an additional <br />factor that is of importance for potential subsidence or stability problems in the vicinity of <br />the outcrop barrier pillar. The old coal fires, when reaching to significant depths into the <br />mountain, created a void space; the overburden lost its support and subsided. Distinct <br />fractures may have been developed above such subsidence features as described by <br />Dunrud (1976) in the Somerset - Paonia area. <br />It is evident that potential subsidence or stability problems in the vicinity of the <br />outcrop barrier pillars cannot be ruled out. Landslides of a significant extent have <br />developed close to the coal outcrop at the old Farmers Mine; it cannot be ruled out that <br />they are related to the collapse (crushing or sliding) of the outcrop barrier pillar as the <br />mining proceeded too close to the outcrop. <br />n <br />U <br />PR-08 - 12 - 07/03 <br />APPk.avED <br />9~~-S/o 3 <br />