Many underground injuries are caused by the detachment and falling of rock fragments from rock masses in mines, which are unstable. For this reason it is considered important to have a means whereby the integrity, i.e. the stability or otherwise, of a rock mass can be assessed before mine workers enter the mine working and are exposed to potential injury from falling rock fragments caused by underground shifts.
A technique which has been in use for many years to assess the integrity of a rock mass in a mine working, typically a hanging wall, involves tapping the rock mass with a hammer or with a sounding bar, also known as a pinch bar and listening to the sound generated and making an assessment of the integrity of the mass according to the sound which is heard. The sound which is heard is caused primarily by the acoustic wave generated through vibration of the rock mass and other sources, for example the sounding bar, in the surrounding environment. The sound has a unique frequency distribution which must be interpreted in order for a determination to be made of the integrity of the rock mass.
The inventor is aware of techniques used for providing objective acoustic assessments of the integrity of rock masses. These techniques are based on the automated analysis of the acoustic signals being generated by the so-called tapping of the rock mass. However, it is desirable to improve the quality of the objective assessment of the rock beyond acoustic measurement techniques.
The present invention aims to provide an improved method of identifying portions of a rock mass presenting an increased rock fall risk by combining acoustic assessment with other assessment techniques.