Through a similarity analysis based on a large number of experimental data for rock indentation, relationships between indentation force and either indentation depth or length of radial/median crack are established. These forces are induced by hemispherical, truncated, or cylindrical indenters. The formulas obtained can serve for general use in various kinds of rock with different diameters of the three indenter types. This analysis provides a great deal of information for practical use, such as full face boring and percussive drilling.
A travers une analyse de similitude basee sur un grand nombre de donnees experimentales sur I'indentation de la roche, on a etabli les relations entre la force d'indentation et soit la profondeur d'indentation soit la longueur de la fissure radiale/medians induite par des indentateurs hemispheriques, tronques, et cylindriques. Les formules obtenues peuvent servir à une utilisation generale dans differentes categories de roches avec des diametres differents pour les trois types d'indentateurs. Avec cette analyse, on a obtenu d'importantes ameliorations pour les applications pratiques, comme pour Ie forage par explosion et Ie forage par percussion.
Durch eine Similaranalyse einer groβen AnzahI von experimentell gewonnenen Daten zur Gesteinsintrusion werden Verhaltnisse zwischen Intrusionskraft und Intrusions- Tiefe oder zwischen Intrusionskraft und Lange der radialen/medianen Spalte hergestellt. Diese Krafte werden durch hemispharische, stumpfe oder zylindrische Druckwerkzeuge verursacht. Die erhaltenen Formeln können allgemein auf verschiedene Gesteinsarten mit verschiedenen Durchmessern der Druckwerkzeuge angewandt werden. Diese Analyse liefert viele Informationen fuer die Praxis, beispielsweise beim Vollschnittvortrieb und bei der Schlagbohrung.
Full face boring, percussive drilling, and drag bit cutting are today the most frequently used mechanical excavation methods for medium or hard rocks. However, the basic mechanisms involved in them are still not fully understood. Rock indentation by a bit is the fundamental mechanism in most mechanical excavation methods. Therefore, the investigation of the indentation mechanisms is important for improvement of rock excavation methods. The main purpose of the present study is to propose a reasonable model for predicting the indentation depth and the radial/median crack distribution in rocks induced by different types of indenter. The former is important for the improvement of rock excavation efficiency. The later is important for the analysis of the hydraulic conductivity in the near-field of a nuclear waste storage. It can also contribute to understanding of the mechanisms of mechanical excavation and the improvement of excavation tools.
Four types of Swedish rock, namely Kallax gabbro, Bohus granite, Ekeberg marble, and Lemunda sandstone, were tested in indentation by using two displacement-controlled rock mechanics testing machines, Instron 0–100 kN and Instron 0–4500 kN, with maximum loads ranging from 15 to 150 kN. Their mechanical properties are given in Table 1, where c, E, v and G are uniaxial compressive strength, Young's modulus, Poisson's ratio and energy release rate, respectively. Three kinds of indenters, namely hemispherical, truncated and cylindrical, were used in the indentation tests. The dimensions of the rock sample were selected to avoid if possible crack propagation longer than half way through the sample for the strongest rock loaded to 100 to 150 kN. The sample diameters were much larger than the diameters of the indenters, and confined in a manner similar to the confinement provided in a semi-infinite rock mass during the indentation process. A constant indentation rate of 0.05 mm/s was applied for all experiments. This approximately corresponds to 1x 10–8 of the wave speed of rock material and therefore, the load can be treated as static. After indentation tests, the samples were cut in slabs, and the cracks in the samples were observed under a fluorescent light by introducing a fluorescent substance inside them (Lindqvist et al., 1994).
