Research on the guided wave reflecting from the upper interface of partially grouted rock bolt

Finite element method was used to simulate longitudinal guided wave reflecting from the upper interface of partially grouted bolt, with the excitation wave frequencies 5~60 kHz. Reflection coefficient was used to evaluate the upper interface reflection wave which can be seen clearly while reflection coefficient was large. The effect of thickness of the grout layer, wedge angle between the upper interface and the bolt axial direction and grout materials on the upper interface reflection wave was studied. The results show that the factors above have little effect on reflection coefficient with the same excitation wave frequency, and reflection coefficient is larger when the excitation wave frequency is lower than 20 kHz, and reflection coefficient reaches its minimun when the frequency is 40 kHz. The results of numerical simulation agree well with the experimental results.