RBT Instrument for Inspection of Rock Bolts Using Guided Waves

Stepinski, Tadeusz; Akademia Gorniczo-Hutnicza im Stanislawa Staszica w Krakowie; Poland

Tadeusz, S.; Akademia Gorniczo-Hutnicza im Stanislawa Staszica w Krakowie; Poland

ID: ECNDT-0411-2018
Session: Civil Infrastructure - ET, UT
Room: J1
Date: 2018-06-12
Time: 16:00 - 16:20

In this paper we present recent results of rock bolts NDT by means of Rock Bolt Tester (RBT). RBT is a digital instrument for nondestructive inspection of several meters long bolts using guided ultrasound waves. The RBT instrument applies long-range ultrasound to investigate the bolts’ status, especially their grouting condition. RBT features an application tailored ultrasound probe that transmits high-energy, low frequency (chirps in the frequency band 20 to 100kHz), guided waves. The probe’s acoustic coupling to the bolt surface is facilitated by strong permanent magnets. The RBT’s receiver is capable of sensing weak echoes reflected from discontinuities at the bolt’s surface as well its end-echo that have propagated in the range of up to eight meters in a pulse-echo mode. The RBT is a portable, battery-supplied instrument that includes a specially designed analog electronics for generation and reception of guided waves and an embedded digital PC computer for signal processing, operator communication and data storage.

Results of the RBT’s evaluation on rock bolts installed at a number of sites (tunnels and mines) are presented in the paper. A number of test rock bolts with different lengths in the range of 2 to 4 m, provided with artificial damage, have been used for the RBT’s sensitivity verification. The test bolts were manufactured by shielding a certain steel bolt length with plastic tube sealed with silicon. More that 3,000 tests have been conducted until now; the selected results are presented in the paper for illustration and some of them are compared with those obtained using the Swedish instrument Boltometer designed in 70ies but still used in Scandinavia.