Experimental Study of the Effect of Axial Load on Stress Wave Characteristics of Rock Bolts Using a Non-Destructive Testing Method

Traditional rock bolt inspection methods are destructive and limited. Non-destructive testing (NDT) based on the stress wave method can realize a fast and convenient quality detection of rock bolts. To verify the effectiveness of the stress wave-based anchor NDT method, a multi-functional experimental bench was customized on the basis of a bench-pull tension testing machine. Stress waves can be generated by applying axial loads on rock bolts and then collected using a non-destructive tester. The VMD decomposition method and Hilbert-Huang signal processing method were used to filter and analyze the stress wave signal. The influence of the axial loads of different magnitudes on the stress wave was then investigated. The results showed that the stress wave characteristics of the rock bolt changed with the increase in the axial load. It was found, correspondingly, that the stress wave amplitude decreased gradually and there was a trend of rapid decrease at the beginning and then a slower decline. The change in the time domain amplitude of the stress wave after noise reduction can be used to determine the magnitude of the load on the rock bolt during the elastic deformation stage. Further studies showed that the axial load on rock bolts inversely calculated by the stress-wave time-domain amplitude method is accurate and reliable, which can be validated by comparing the data measured by the rock bolt dynamometer. The research results shed light on the development of the NDT technology on rock bolt inspection, and make this testing method more convenient, efficient, and accurate.