Properties of torsional guided wave propagating in grouting bolts

The propagation characteristics of torsional guided waves in grouting bolts were theoretically studies. Firstly, dispersion equations of torsional guided wave propagation in two-layer structure of grouting bolts were established, then energy velocity and attenuation dispersion curves were calculated and displacement distribution characteristics of guided waves were obtained. Results show that: (1) In the frequency range of 500 kHz, only three torsional guided wave modes exist in grouting bolts, which are T(0, 1), T(0, 2) and T(0, 3), and the three guided wave modes are dispersive. As frequency increases. guided wave energy velocity increases as well, and the attenuation value of guided wave decreases. (2) T(0, 1) guided wave mode with frequencies of 50 kHz and 200 kHz maintains large circumferential displacement inside the bolt, which means that the guided wave mode is suitable for bolt flaw testing. Meanwhile the guided wave mode maintains large circumferential displacement in the bolt/grout interface, which leads to guided wave energy leakage from bolt into grout media, and guided wave attenuates significantly. (3) When guided wave frequency is higher than 100 kHz, the varying of bolt diameter has almost no effect on T(0, 1) mode guided wave energy velocity, At the meantime, when guided wave frequency is lower than 100 kHz, T(0, 1) mode guided wave energy velocity decreases as the increasing of grout media'elastic modulus.