Use of the ultrasonic method to investigate distribution of the elastic parameters of rocks in interchamber pillars

Abstract

At the Dzhezkazgan deposit the increasing depth of the mine workings has led to several cases of unjustified high losses of ore left in the pillars.This has made it necessary to determine the optimum parameters of the room-and-pillar system of working.A successful and practical solution to this problem is assisted by the use of mining geophysics to make a detailed investigation of the state of stress and the elastic properties of the rocks in the pillars, and of the disturbed zones induced by shaping of the pillars by drilling and blasting.This article gives certain results obtained by the use of ultrasonic sounding to investigate the elastic properties in a circular interchamber pillar (diameter 9 m, height 7 m) composed of strong flne-gralned sandstone and located in a horizontal bed of mine No. 45 (+235 horizon).A prel~m~nary inspection of the exposed surface of this pillar showed that its rocks are broken up by a network of cracks and mlcrocracks running in all directions due to drilling and blasting.

Use of piezoelectric transducers to measure dynamic stresses in elements of mine working

“…This depth was adopted to avoid the influence of r~e zone of fracture on the readings [4]. When the transducers were fixed in the holes, they were oriented in the required directions.…”