Experimental Technique For Aperture Studies of Intersecting Joints

Hakami, E. (Royal Institute of Technology. Stockholm) | Stephansson, O. (Royal Institute of Technology. Stockholm)

OnePetro 

ABSTRACT:

The ground water flow in crystalline rocks is governed by the properties of the joints. The flow will show different channelling characters depending on the aperture variation on the joint planes and along their intersections. An experimental technique has been developed to study apertures of intersecting joints that includes drilling of cores joints grouted with polyurethane. The grout layer thickness is assumed to represent the in-situ aperture. The thickness variation of the grout layer is measured on sections of a core and analysed statistically. The results so far show that this technique can provide valuable information on the hydraulic properties of joints.



RESUMÉ:

L'ecoulement de la nappe phreatique dans des roches cristallines est gouverne par les proprietes des diaclases. L'ecoulelement montrera des differents caractères de canalisation, dependants de la variation de l'ouverture dans les plans des diaclases et le long de leur intersections. Une technique experimentale, qui inclut forer des carottes de diaclases injectees du polyurethane, a ete developpee pour etudier des ouvertures de diaclases qui se coupent. On suppose que l'epaisseur de la couche de resin represente l'overture in situ. La variation de I'epaisseur de la couche de polyurethane est mesuree dans des coupes d'une carotte et soumise à une analyse statistique. Les resultats jusqu'à present montrent que cette technique peut fournir une information de valeur sur les proprietes hydrauliques de diaclases.



ZUZAMMENFASSUNG:

Die Grundwasserströmung in kristallinen Gesteinen wird durch die Eigenschaften der Kluefte regiert. Die Strömung wird verschiedene kanalbedingte Merkmale zeigen, die von der Öffnungsvariation in den Klueftebenen und langs ihrer Schnitte abhangen. Eine Versuchstechnik, die das Bohren von Kernen aus mit Polyuretan injizierten Klueften einschlieβt, wurde entwickelt, um Öffnungen von sich schneidenden Klueften zu studieren. Es wird angenommen, daβ die Polyuretanschichtdicke die in situ Öffnung darstellt. Die Dickevariation der Polyuretanschicht wird an Schnitten eines Kerns gemessen und statistisch untersucht. Die Ergebnisse bis jetzt zeigen, daβ diese Technik wervolle Information ueber die hydraulischen Eigenschaften von klueften liefern kann.



1 BACKGROUND

Ground water flow and transport play an important role in environmental engineering problems. In particular this is evident in the safety assessment of underground storages for nuclear waste. To be successful in this task we need to be able to model and predict the ground water movements. Experience on ground water modelling and predictions has grown considerably during the last decade. In Sweden the knowledge is very much based on the results of the Stripa Project. One of the main out comings from the Stripa Project was the development of the discrete network modelling where the flow is modelled only through the fractures in a fracture network. The discrete modelling gives the possibilities to include the transmissivities of each single joint in the calculation (e.g. Dershowitz (199)). The connectivity between the joints, that is the character of the intersections, is also a part of the conceptual model. However, there is a lack of experimental data on the aperture at joint intersections. Therefore, we wanted to include the intersections in a study of aperture distribution of natural rock joints.



2 PERMEABILITY OF JOINTED ROCK

The permeability of rock masses varies strongly between different regions of the ground. The reason to this is the wide variation in the fracture systems that governs the pore structure open to flow. There are several factors influencing the permeability of the rock mass.



2.1 Geological conditions

The geometry of the pore structure in the fracture system is dependent on the geological conditions. The geological history of the area determines the different rock types. Tectonic stresses have given rise to fractures and displacements in the rock. Different geochemical conditions have produced joint filling materials of different kinds.