The integrity of grouting bolt was tested using ultrasonic guided wave nondestructive inspection method. Ultrasonic guided wave test platform was firstly established, and pulse-echo method was applied for ultrasonic guided wave testing. Then reflected waves from upper interface of grouting bolt was studied, and the results show that the upper interface reflected wave's reflection coefficient reaches its maximum value in the excited wave frequency range 0~100 kHz, when the frequency is 55 kHz, and excited wave frequency ranging from 50 to 60 kHz is suitable for bonding density testing. As the ultrasonic guided wave velocities propagation in a free bolt are faster than those propagation in the bonding section of grouting bolt, time difference between the upper interface reflected wave and bolt end reflected wave will decrease while the de bond section of grouting bolt increases. As a result, by difference value of measuring time, bonding density of grouting bolt will be easily determined.
Grouting bolts are the main support form used in non-ferrous metal underground excavation formed rock mass tunnels. Due to construction or long-term service and other reasons, the integrity of the grouting bolt's composite structure will reduce gradually, which will affect bolt's supporting effect. The traditional way to test the effect of bolt support system is pull-out test, it is a destructive test and it will cost a lot of time and money (Zou 2004). During the past ten years, researchers tried to use active ultrasonic guided wave nondestructive testing technology to evaluate the integrity of grouting bolts and have achieved initial research results. For example, Beard used elastic element to elaborate the bonding condition on the surface between bolt and anchoring agent, and he has also analyzed how the bonding condition's diversification influenced ultrasonic guided wave's dispersion curves (Beard & Lowe 2003).