Non-destructive testing of rock bolt fastening as an element of monitoring the state of mine workings

Abstract

Purpose. To substantiate the informative parameter, to develop the method and equipment for non-destructive testing (NDT) of rock bolt fastening, as an element of geomechanical monitoring of the mine workings state. Methods. Analytical and bench experimental testing of shock-wave processes in the “rock bolt – bonding layer – rock massif” system. Findings. It has been established, that the non-destructive shock-wave method is the most satisfying for monitoring the geomechanical state of the “rock bolt – bonding layer – rock massif” system. This method is based on the regis-tration and analysis of rock bolt oscillations, caused by non-normalized hit to the rock bolt end. It has been con-firmed, that the most informative parameter is the relaxation time, that is the time over which the amplitude of oscillations decreases by “e” times. It has been shown, that clamping of the resin-grouted rock bolt in massif and its ten-sioning affects the relaxation time of damped oscillations. Furthermore, the relaxation time is inversely proportional to the degree of the rock bolt clamping, and is linked linearly with an increase in the rock bolt tensioning. The spec-tral composition of wedge shaped rock bolts self-oscillations, which are caused by impact excitation, depends both on the nature of clamping and on the rock bolt length, and makes it possible to identify the rock bolts by their length. Originality. The existence of a special type of damped longitudinal oscillations of the rock bolt in viscoelastic medi-um of the bonding layer has been established. The relaxation time of the specified type of oscillations was chosen as an informative parameter. An analytical link has been established between the informative parameter of shock-wave method of monitoring and the main indicators of rock bolt fastening quality: the degree of adhesion with massif and tension value. Practical implications. The method has been improved and equipment has been developed for non-destructive testing of rock bolt fastening, which makes it possible to control in-situ the rock bolt fastening quality, including the geomechanical state monitoring of mine workings.