Integrity evaluation of grouted rock bolts using reflected guided ultrasonic waves

As one of the main support systems in the reinforcement of underground structures and rock slopes, rock bolts have been commonly used. Destructive pull out tests have been used to investigate the integrity of the rock bolts. Furthermore, a non-destructive technique using transmitted guided ultrasonic waves was suggested. Note for the transmission method, the source of the ultrasonic waves should be installed on the end of the steel bar during construction of the rock bolts in the field. The purpose of this paper is to suggest a reflection method using guided ultrasonic waves to evaluate the integrity of the grouted rock bolts in the laboratory. Steel bar with 3.1m in length and 25.4mm in diameter are grouted with different defect ratio ranging 0-100%. The diameter of the cement grouting is 38mm. The guided waves are generated by PZT element. The reflected guided waves are measured by AE sensor at the end of the grouted rock bolt. The wavelet transform is used to calculate the energy velocities of the reflected guided waves. The results show that the energy velocities of reflected guided ultrasonic waves increase with the defect ratio. Furthermore, the velocities calculated by the reflection method are similar to velocities by the transmission method. This research demonstrates that the reflection method for the rock bolt integrity may be effective method for the integrity evaluation of the grouted rock bolts.