Effects of Surface Topography on the Stability of Coal Mine Openings.
Molinda-GM; Heasley-KA; Oyler-DC; Jones-JR
Proceeds 10th Int'l Conf Ground Control in Mng Morgantown West Virginia, 6/10-12/91 WVU PP 151-160 :151-160
An investigation was conducted to determine the nature and frequency of coal mine roof failure beneath valleys. A mechanism for this failure and suggestions for controlling this problem are presented. Hazardous roof conditions identified in a number of mines were positively correlated with mining activities beneath stream valleys. Mine maps with overlays of unstable roof and locations of stream valleys show that 52 pct of the instances of all unstable roof in the surveyed mines occurred directly beneath the bottom-most part of the valleys. The survey also showed that broad, flat-bottomed valleys were more likely to be sites of hazardous roof than narrow- bottomed valleys. Evidence of valley stress relief was found beneath a number of valleys in the form of bedding-plane faults and low-angle thrust faults. This type of failure, previously believed to be only a shallow phenomenon, was found at mining depths as great as 300 ft. In situ horizontal stress measurements in a mine beneath a valley and the adjacent hillsides confirmed valley stress relief. Underground mapping showed that roof falls in excess of 100 ft in length and up to 25 ft high closely aligned with the valley axis. Numerical analysis of 13 valleys overlying one mine property showed the effect of the valley excavation on horizontal and vertical stress. Thickness of cover, valley shape, and the orientation of the valley relative to the maximum regional horizontal stress all influence the "valley effect" on roof stability.
Proceeds 10th Int'l Conf. Ground Control in Mng. (Morgantown, West Virginia, 6/10-12/91) WVU, PP. 151-160