Volume 32, Issue 1 (January 2009)
Evaluation of Rock Bolt Integrity using Guided Ultrasonic Waves
Rock bolts play a crucial role in reinforcement support systems for tunnels and rock slopes. In this study documented herein, guided ultrasonic waves are used to evaluate the integrity of rock bolts. The dispersion characteristics of the guided waves are identified by numerical simulations. Experimental studies using the transmission of guided waves are carried out with different defect ratios for grouted nonembedded rock bolts, and for rock bolts embedded into a concrete block and rock mass. Analytical solutions are suggested to estimate the equivalent velocity for both the grouted and the embedment portions. Numerical simulations reveal that the optimal frequency range of guided waves is 20∼70 kHz in the first longitudinal mode. Field and laboratory experimental studies and associated analyses show the velocity of guided waves increases as the defect ratio increases. The velocity for the grouted portion in the nonembedded rock bolts is essentially constant. However, the velocity in the embedment portion decreases with increasing embedment length due to the increase in the size of the influence zone. Results suggest that the integrity of rock bolts can be easily evaluated by the transmission method using guided waves.