Nondestructive evaluation of grout defect in rock bolt using electromagnetic waves

This study aims to inspect grout defects in rock bolts using electromagnetic (EM) waves. The experiments are conducted using one intact rock bolt and eight defective rock bolts with defect ratios (DR) of 10–50%. A two-conductor transmission line is configured using a pair of rock bolts to transmit EM waves. The EM waves are generated and detected using a time-domain reflectometer. Consequently, the velocity of the EM waves increases with increasing DR. Additionally, almost identical velocities are observed at the same DR, regardless of the defect locations. Moreover, the EM wave reflections are observed at these defects. The defect locations are estimated using the velocity and reflection time of the defects. The estimated location is in good agreement with the actual location. This study demonstrates that EM waves can be an effective tool for evaluating grout defects in rock bolts.