Method for Identifying the Grout Defects of the Anchors at Ultra-Early-Stage Based on Time-Domain Waveform Characteristic Reflection Points

Anchors constitute a common form of structural support in geotechnical engineering. Precise identification of ultra-early-stage (UES) anchoring quality is crucial to ensure the integrity of the secondary lining. To address grout defects in the UES of anchors, a calculation method for UES anchor wave velocity was introduced. Indoor experiments and numerical simulations were conducted for non-destructive testing (NDT) of anchors in the UES, analyzing time-domain waveform characteristics and wave velocity variations. A method for identifying grout defects in the UES of anchors was proposed. The results indicate that the proposed wave velocity calculation method offers a more precise estimation of UES wave velocity for anchors compared to the traditional approach. This enhancement enables a more precise evaluation of the development of solid phases in the anchoring medium. As the solid phase develops, the wave velocity and first wave amplitude of the anchor gradually decline, while the response time of the bottom reflection increases. Grout defects lead to amplified amplitudes in both time-domain and frequency-domain signals, accompanied by a heightened occurrence of peaks in the frequency domain. The waveform distortion region before the bottom reflection is caused by grout defects. In the time-domain signals of defective anchors, a waveform distortion region is observed before the bottom reflection. By assessing the magnitude of the absolute value of the ratio between the amplitude of characteristic reflection points within the distortion region and the amplitude of the first wave, effective identification of grout defects in the UES of anchors can be accomplished.