Experimental and numerical studies on group velocity of ultrasonic guided waves in rock bolts with different grouted ratios

Nongrouted parts of rock bolts can adversely affect the stability of tunnels and rock slopes. The objective of this study is to evaluate grouted ratios of rock bolts using ultrasonic guided waves. Experimental and numerical models are composed of three-layered (steel bar, grout, and concrete) rock bolts that can provide accurate propagation characteristics of ultrasonic guided waves. Group velocities of ultrasonic guided waves are analyzed using wavelet transforms. Experimental and numerical results show that group velocities decrease with increasing grouted ratio. Results of this study demonstrate that group velocity can be used as an indicator for evaluating grouted ratios of rock bolts.