The aperture distribution of a rock fracture can be studied with different experimental methods. The methods are based on (I) surface topography measurements, (II) resin injection or (III) casting techniques and are briefly reviewed in this paper. Differences between the methods are discussed and parameters that may be chosen in presenting the results are recommended.
La distribution de l'espace fissural peut être etudie avec differentes methodes experimentales. Ces methodes sont basees sur (I) des mesures de la topographie de la surface, (II) des techniques d'injection de resines ou (III) de moulages; celles ci sont brièvement passees en revue. Les differences entre les methodes sont discutees et les paramètres qui pourraient être choisis pour la presentation des resultats sont recommandes.
Kluftoffnungsveneilungen können mit verschiedenen experimentellen Methoden untersucht werden. Die drei meistverwendetene Methoden sind:
Messong der Kluft-Oberflachentopographien,
Injektion von hartenden Kunststoffen und
Diese Methoden werden zuerst kurz beschreiben, worauf die wesentlichen Unterschiede diskutien werden. Zum Schluss wird kommentiert, welche Parameter zur Beschreibung der Kluftöffnung mit diesen Methoden ermittelt werden können.
Fractures have a major influence on rock mass behaviour, and fracture studies have always been a central pan of rock mechanics. Ground water flow in rock is today an important research area, mainly in conjunction with the assessments of underground disposal of hazardous waste. As a consequence, many rock mechanics researchers have focused on the hydromechanical properties of rock fractures during the last decade. The conductivity of a rock fracture is governed by the geometry of the void space between the two fracture surfaces. This geometry is complex and its detailed nature is not very well known. The aim of this paper is to give a very brief review of methods and parameters that have been used to measure and describe the fracture void geometry.
The measurement methods can be grouped with regard to the basic measurement procedure (see Figure 1). One procedure (I) is to measure the topography of the two fracture surfaces on each side of the void space and to define the aperture as the space between the surfaces. Another procedure (II) is to inject resin into a fracture to fill up the void space. The specimen containing the fracture can then be cut into slices and the aperture be measured as the resin thickness along the fracture intersections on each slice. A third procedure (III) is to make a replica of the void space between the surfaces of a fracture, or to make replicas of the fracture surfaces. The different methods are explained in some more detail as follows.
This approach has been used by Gentier (1986). The topography of a natural granite fracture was measured with a profilometer, a mechanical device which has a stylus that moves on the surface. For each fracture surface the surface heights and the location along fracture profiles is continuously recorded. The opposite profiles are matched and the resulting aperture is calculated. The difficulty with this method lies in the matching of profiles since it is difficult to measure the exact relative position of the profiles. Also the size of the profilometer stylus will determine the accuracy of the measurement. An analogous procedure was used by Iwano & Einstein (1993 and 1995). They used a laser beam profilometer to measure the surface topography of the two fracture surfaces. Five fracture specimens from different rock types were included in their study. The size of each sample was 25 cm2 and the spacing between measurement points was 1 mm.