Nondestructive procedure for testing grouting quality of rockbolt anchors

A nondestructive method for testing rockbolt anchors has been preliminary tested in the laboratory and in the field. The testing is performed by a new testing device mounted firmly on the bolt head. No special adjustment of the bolt head is neccessary to mount the device and to perform testing. The device triggers oscilations of the grouted bolt by a small hammer. Acceleration history of the device in the direction of the bolt axis is recorded and the dominant frequency is determined. A correlation between the dominant frequency of the grouted bolt and the percent of the bolt length grouted to the rock around the borehole is established in cases when it is evident that the grout properly fixes the bolt at least near the head. No preparation of bolt head required, the simplicity of use of the measuring device, as well as the ease and short time of testing, are principal advantages of the method.