The quality evaluation of the grout in rock bolts based on the stress wave propagation

Abstract

Nondestructive testing of rock bolt is essential for evaluating the grouted quality in rockmass. The stress wave propagation in the fully grouted rock bolts and defectively anchored bolt was investigated, where the mortar between the rock and bolt is subjected to different curing ages and stress wave induced by a dynamic excitation hammer impacting the bolt. First of all, it is found that both velocity and amplitude decrease with the increment of curing age of the anchor agent, based on the experiment of stress wave propagation in the fully grouted rock bolts. Velocity and amplitude attenuation decrease drastically within the first 14 curing ages and maintain steadily thereafter. The energy proportion manifests no change in the same waveform with the increment of curing ages, but the proportion taken by high-frequency harmonic wave increases. The crossing point of energy proportion curves moves towards low-frequency area, whereas the decrease of total energy tends to be stable. Secondly, the experiment of stress wave propagation in anchored bolt with different size of defects is also investigated. The variation of velocity and amplitude of stress wave in the defectively anchored bolt is similar to that of stress wave propagation in the fully grouted rock bolts. The crossing point of energy proportion curves moves towards low-frequency area, which is similar to the fully grouted rock bolts. But the velocity and amplitude attenuations in defectively anchored bolt are less than those in fully grouted rock bolts. The larger the defect size is, the smaller the amplitude attenuation is. Finally, the experiment of stress wave propagation in anchored bolt with different location of defects is also conducted. The magnitude of amplitude attenuation increases with the increase of distance. But the crossing point of energy proportion curves remains unchanged. The anchoring quality of bolts can be evaluated by the anchoring effect of anchoring agent, which can be estimated by the attenuation amplitude of stress wave velocity and amplitude, based on the experiment of stress wave propagation in defectively anchored bolt.