Fracture Mechanics of Rocks.

Abstract

This paper reviews recent studies on (1) AE (acoustic emission) and cracking models, (2) failure processes and (3) frictional sliding processes, mainly based on work carried out in Japan. Techniques for AE data acquisition and hypocenter location have been greatly improved; one system can record twenty-one channels of waveforms and can locate the AE hypocenter automatically. Another system can also record the occurrence time and the maximum amplitude of the AE event without dead time. On the basis of these data, we are able to discuss the relation between the distribution of the hypocenters, the occurrence intervals, and the experimentally controlled physical parameters. For this purpose, many studies have tried to develop quantitative expression for the statistical characters of these distributions. Techniques for evaluating AE source parameters are still being developed; and there has been a great deal of improvement in our knowledge about cracking mode of AE. The focal mechanisms have been systematically studied based on the space distributions of the initial motion directions. The studies showed that shear type cracking becomes dominant with increasing axial stress. These mechanism solutions agree well with the local stress field suggested by the fracture plane. Increasing of the failure strength of rocks with increasing stress and strain rates under relatively low confining pressure has been studied experimentally. The failure process and the rate dependency of the fracture strength in the low pressure regime are discussed on the basis of a stress corrosion cracking model. The failure mechanism under higher confining pressures of up to 3GPa is also examined. Some behavior including the variation of AE activity with axial stress differs between low and high confining pressures although the stress-strain relations clearly show brittle deformation in both regimes. On the basis of these differences, the researchers proposed that 'high-pressure' brittle deformation was different from ordinarily observed brittle behavior at low pressure, and examined the failure micromechanisms through an optical and an electron microscopes. Frictional sliding has also been intensively examined in the past decade. Experiments using large samples have demonstrated that the slip propagation process is well described by a slip-weakening model. The relations between the dynamic parameters of slip propagation process and the physical parameters of slip surfaces is becoming clearer.

Velocity Measurements and Crack Density Determination During Wet Triaxial Experiments on Oshima and Toki Granites

“…Following the technological advances made in AE location (LOCKNER et al, 1991;MOORE and LOCKNER, 1995;KUSUNOSE, 1995);LEI et al (1998LEI et al ( , 2000 and JOUNIAUX et al (2001) have developed an AE localization technique (for details see LEI et al, 1998). Figure 2 presents a schematic view of the sample-piston-data recording arrangement.…”

Source analysis of acoustic emissions in Aue granite cores under symmetric and asymmetric compressive loads

“…Spatial and temporal changes in AE microfracturing patterns (Lockner 1996) and the correlation of AE hypocentre pairs have been used to analyse the localization of deformation during rock failure tests (Hirata et al 1987; Lockner & Byerlee 1993). State‐of‐the‐art techniques for laboratory mapping of AE hypocentres are summarized in Lockner (1993) and Kusunose (1995). AE focal mechanisms have also been analysed with some success.…”