All underground construction in rock demands rock support. The most common method today is to install rock bolts anchored with cement grout.  It is of vital importance for the safety to check that rock bolts are installed in a proper and professional way by a sub-contractor. This may either be done by pullout tests, which unfortunately is a time-consuming and destructive way, or by the non-destructive testing (NDT) technique verified in this report. Today, there are only 3-4 of the old Boltometer instruments still in operation. The measurement technique is robust but old. Therefore, Geosigma initiated a project in 2010 to develop a new instrument, the Rock Bolt Tester (RBT) based on the same basic principle as the Boltometer, ultrasound technique, but with modern electronics, new communication platform, and easier operation.

The aim of the project was to verify the functionality and performance of the RBT to facilitate RBT’s acceptance by the market as well as the Swedish Transport Administration (Trafikverket) as a complement and possibly replacement for the Boltometer. The project has included comparative measurements with the Boltometer and the RBT on about 100 rebar bolts as well as overcoring of some bolts with defects in the grouting.

The results of the comparative measurements in Dannemora mine, Äspö Laboratory and Stockholm Bypass, show that the RBT is more sensitive than the Boltometer to the defects occurring in the grouting and also that the methods give similar results. The overcoring, even though performed for a limited number of bolts, showed that RBT is sensitive even for small defects in the grouting. The tests performed on combination bolts, like the PC-bolt and CT-bolts that were installed at Äspö HRL, gives promising results but much more tests are needed to verify the RBT’s functionality on these bolt types. This may also be a new application area for the RBT in the near future.