PERMFILE134368 - Laserfiche WebLink

Home Browse Search

Sanborn Creek Project Paqe 16 subsidence effects calculations for the "D" ground surface for mining the various size, retreat pillars planned in the "C" and "B" appropriate low-cover, 1250-foot depth, and depth in the Sanborn Creek Mine. August 21, 1992 Seam, "E" Seam and the 20-foot high, robbed Seams at individually high-cover, 2500-foot The calculated trough subsidence tensile stains, approaching 30000 micro-strain in the "D" Seam under low-cover, is sufficient to open large fractures. At the York Canyon Mine in New Mexico, 34000 micro-strain produced tension fractures at the ground surface over 3 feet wide and at least ten feet deep. The location of the predicted maximum tensile strains in the overlying "D" and "E" Seams is directly over the underlying barrier pillar ribsides, the sides and ends of the panels. Robbing of the Sanborn Creek Mine panel pillars will probably open similar size fractures along joint weaknesses in the rock below the water-filled overlying Oliver No. 1 Mine workings along the line of the underlying barrier pillar ribsides. It is not suggested that an inrush will develop. However, it is predicted that water impounded in the Oliver No. 1 Mine will find a way to take advantage of the increased permeability accompanying tensile strain to drain into the Sanborn Creek Mine workings. The increased permeability accompanying pillar crushing in the "C" and "B" Seams may progressively drain . any water impounded in the Hawk's Nest Mine workings. The maximum calculated "E" Seam tensile strain, 16300 micro-strain under low-cover and 12900 micro-strain under high-cover as shown on Table • 4, is sufficient to open up any bedding plane and joint weaknesses present. If water is impounded in the Hawk's Nest Mine workings it must be anticipated that it will find a path to slowly drain into the Sanborn Creek Mine. "C" AND "D^ SEAM INTERACTION ANALYSIS The Oliver No. 1 Mine, which operated in the late 1930s and the 1940s, room and pillar mined part of the "D" Seam overlying planned mains, sub-mains and a few of the planned panels in the Sanborn Creek Mine. Water was seen ponded at the portal of the Oliver No. 1 Mine. The water apparently impounded in the Oliver No. 1 Mine workings presents a potential hazard. It is remotely possible, but extremely unlikely, that a chimney collapse could propagate between the "C^ and "D" Seams and suddenly release the impounded water. It is probable that robbing of panel pillars during retreat from the planned panels will produce tensile strains of such a magnitude that the resulting increased formation permeability will progressively drain water from the overlying Oliver No. 1 Mine. It is, therefore, recommended that the Oliver No. 1 Mine be pre-drained prior to pillar robbing in underlying panels in the Sanborn Creek Mine. •