The ISRM Suggested Methods for Rock Characterization, Testing and Monitoring: 2007-2014

With its portable, simple and affordable attributes, the Schmidt hammer (SH) is an ideal index apparatus, which underlies its increasing popularity and expanding range of applications. The SH rebound hardness value (R) is perhaps the most frequently used index in rock mechanics practice for estimating the uniaxial compressive strength (UCS) and the modulus of elasticity (E) of intact rock both in laboratory conditions and in situ. The SH is also widely used for estimating the (UCS) of discontinuity walls and assessing the workability, excavatability and boreability of rocks by mechanical means (cutting, polishing, milling, crushing and fragmentation processes in quarrying, drilling and tunneling).

The properties of rocks under dynamic loading are important for the study of a whole range of rock mechanics and rock engineering problems, including blasting, protective design, explosives storage, rock bursts and seismic events. The propagation of dynamic stress waves in the ground, response of rock tunnels to dynamic load, dynamic support design and damage assessment all require a good understanding of the behavior of rocks under dynamic loading. Due to the transient nature of dynamic loading, the dynamic tests of rock material are very different from static tests.

The International Society for Rock Mechanics has so far developed two standard methods for the determination of static fracture toughness of rock. They used three different core-based specimens and tests were to be performed on a typical laboratory compression or tension load frame. Another method to determine the mode I fracture toughness of rock using semi-circular bend specimen is herein presented. The specimen is semi-circular in shape and made from typical cores taken from the rock with any relative material directions noted. The specimens are tested in three-point bending using a laboratory compression test instrument. The failure load along with its dimensions is used to determine the fracture toughness. Most sedimentary rocks which are layered in structure may exhibit fracture properties that depend on the orientation and therefore measurements in more than one material direction may be necessary. The fracture toughness measurements are expected to yield a size-independent material property if certain minimum specimen size requirements are satisfied.

3D laser scanning techniques have been developed since the end of 1990s for 3D digital measurement, documentation and visualisation in several fields including 3D design in the processing industry, documentation and surveying in architecture and infrastructure. By using a 3D laser scanner, a tunnel or underground construction can be digitised in 3D with a fast scanning speed and high resolution up to millimetre level. The scanning data consists of, not only X-Y-Z co-ordinates, but also high resolution images, either gray-scale (with reflex intensity data) or colour (with RGB data), and then can be transformed into a global co-ordinate system by control survey. Therefore, any rock engineering object with its as-built situation can be quickly recorded as the 3D digital and visual format in a real co-ordinate system. In this case, it provides a potential application for 3D measurement, documentation and visualisation with high resolution and accuracy. In order to investigate the current development of the state-of-the-art of laser scanning techniques and its potential application to rock mechanics, ISRM therefore set up the ISRM-Swedish National task in 2007 during the ISRM Congress in Lisbon through the Swedish Rock Mechanics Group (BeFo). The task focused on three parts: (1) Investigate the state-of-the-art in the current development of laser scanning techniques; (2) Summarise the application examples by using laser scanning techniques to rock mechanics projects; (3) Evaluate the limits and needs for further development. In this report, the purpose of this study is described first, and then the current development of laser scanning techniques (both hardware and software) is summarised. Based on the literature review and some case studies, the current status of the application of laser scanning techniques to rock mechanics is presented. Finally, the limits of current development and the needs for further development are discussed.