Variation characteristics of anchor’s dynamic testing signal on the conditions of tensile load

Non-destructive testing for rock bolts in this study considers loads typical of anchors in practical engineering. The non-destructive testing experiment has been conducted for bolts under various load levels with variation characteristics of the dynamic testing signal and analyzed based on the stress wave reflection method. This research indicates that reflection signals of the fixed end section are relatively strong while reflection signals of the bottom section are relatively weak, regardless of bolt bearing loads, due to the effect of transmission, reflection and attenuation of the stress wave. The dynamic signal features obvious cycles in addition to the comparatively regular waveform in no-load cases as, with increasing load, dynamic signals become increasingly unstable while mechanical properties change in the anchor rod, anchor medium and the interface. The combination method of wavelet decomposition and multi-scale is applied to the test signal analysis to improve readability and accuracy of the signal. This research indicates that wavelet analysis interacts with non-stationary signals effectively, creating a solution for the reducing signal-noise ratio caused by the load. Obviously, it can also additionally read out the reflected signal of the bottom section, thereby improving the accuracy of anchoring quality interpretation.