A novel method of computation for anchorage length based on the propagation characteristics of anchor excitation stress wave

Detecting the anchoring length is an integral part of the quality inspection of the bolt anchoring, which is crucial to the safety of the roadway support. This paper studies the influence of the anchoring length on the propagation characteristics of the exciting stress wave of the bolt. The research finds that the change in the anchoring length affects the attenuation rate and frequency distribution of the stress wave signal amplitude. Under the same test conditions, the anchoring length negatively correlates with the consolidation wave velocity. The VMD analysis and processing method decomposes the original detection signal once or the characteristic mode function twice. The bottom reflection time is obtained from the bottom reflection signal identified according to the decomposed mode function. Based on the propagation characteristics of the exciting stress wave in the anchor rod, a method of calculating the anchoring length using the bottom reflection time is proposed. Experimental verification of anchoring models for different anchoring lengths is carried out. The calculated results are consistent with the actual anchoring length; the longer the length, the smaller the relative error. The error rate meets the accuracy requirements of on-site engineering tests and guarantees safe production.