Rock Bolt Inspection by Means of RBT Instrument

In this paper we present a new digital ultrasonic instrument for nondestructive inspection of rock bolts using guided waves. The Rock Bolt Tester (RBT) instrument applies long-range ultrasound to investigate bolt’s status, especially its grouting condition. RBT features an application tailored ultrasound probe that transmits high-energy, low frequency (below 100kHz) guided waves and is capable of receiving weak echoes reflected from the discontinuities at the bolt surface as well its end-echo that have propagated in the range of up to four meters. The RBT is a portable instrument that consists of specially designed analog electronics for generation and reception of guided waves and an embedded digital computer for signal processing, operator communication and data storage. Results of the RBT’s evaluation using prepared rock bolts installed at a number of sites (tunnels and mines) are presented in the paper. The test bolts with different lengths in the range of 2 to 4 m were manufactured by shielding a certain steel bolt length with plastic tube sealed with silicon. Plastic end cups were installed on many bolts to create uniform conditions for end echo measurements. Approximately 3,200 tests have been conducted; selected results are presented in the paper for illustration and comparison of the results of the applied signal processing techniques.