Use of ultrasound to determine the state of the roof rocks of mining-out rooms

Abstract

To ensure efficient and safe mining operations, it is important to know the stress in the rock mass around mine workings and its distribution pattern.It is known that mining operations in any rock mass disturb its internal extuilibrium, At the points in the rock mass adjoining the generatrix of the cavity the stresses are redistributed and concentrated around the working, This is the principal physical cause of the change in the properties of the rock around the working.Depending on the rock strength, two types of mechanical state of the rock mass around a working are most frequently observed; corresponding to these, two types of distribution of the acoustic characteristics of the rocks are noted as we go deeper into the rock mass and further from the periphery of the working [1].Rocks with higher stability, i.e., capable of withstanding the total stresses arising at the periphery of tim working and not in need of any support, are characterized by the elastic wave velocity distribution shown in Fig, la: