Building in rock is a highly important activity in today’s society. Densification of large cities and expanding industries place higher demands on underground rock construction. Requirements regarding environmental impact, safety, implementation and installation, and long-term sustainability influences daily decisions in rock construction. There is a need of new and stricter methods for verifying compliance with safety, quality and durability requirements. Control methods can range from administrative checks related to the execution to destructive testing of installed elements. Destructive testing implies that the element being checked is destroyed or to some extent damaged during the testing process. This makes destructive testing a less desirable and more expensive method compared to others. Unlike destructive testing, in Non-Destructive Testing (NDT), the elements tested remain unchanged and functional. Non-destructive testing can be performed using several different methods, including ultrasound, which is one of the most commonly used NDT methods in industry.
For quality assurance of fully grouted bolts, the ultrasonic instruments RBT (Rock Bolt Tester) and Boltometer are widely used in Sweden today. These instruments are primarily designed for non-destructive inspection of the grouting of fully grouted rebar bolts. The rock construction industry today has a great interest in going from the traditional rebar bolts to different types of combination bolts (e.g. end-anchored, fully grouted and sometimes pre-tensioned bolts), due to production advantages thanks to automation but also due to work environment reasons thanks to the immediate bearing capacity that these bolts can achieve.
The instruments RBT and Boltometer are developed to check fully grouted rebar bolts. This implies a limitation of the bolt types that can be used in the industry when quality testing of rock bolt grouting is required.
The purpose of the current project is to further develop the instrument RBT to make it possible to use it to control the grouting of additional bolt types other than steel rebar bolts. The goal is to obtain an instrument that can reliably be used for quality control of the grouting of bolt types PC and CT bolt, and similar combination bolts, installed during the construction of tunnels and rock slopes.
The input from the project reference group during the project is also Appreciated. The following have participated: Per-Erik Söder (Swedish Transport Administration), Tommy Ellison (Besab), Diego Lope Alvarez (SKB), Björn Stille (Aecom), Mattias Roslin (Theta Engineering AB, previously the Swedish Transport Administration) and Per Tengborg (BeFo). The financial support came mainly from the Rock Engineering Foundation – BeFo, but also from Pre Cast Technology AB – Pretec and in-kind from Geosigma.
Stockholm, 2021
Per Tengborg