Tests during pillar robbing, longwall operations, and other mining activities indicate that roof-floor convergence rates can be used as an indicator of imminent roof failure. New instruments provide nonobstructing measurements up to 35 ft away. The ultrasonic transducers can be attached to a roof bolt, placed in an unsupported area (by means of a toss basket), or handheld.
机构:
Philipps-Univ Marburg, Marburg, West Ger, Philipps-Univ Marburg, Marburg, West GerPhilipps-Univ Marburg, Marburg, West Ger, Philipps-Univ Marburg, Marburg, West Ger