The results of a comprehensive laboratory study of the mechanical displacement, permeability, and void geometry of single rock fractures in a quartz monzonite are summarized and analyzed. A metal-injection technique was developed that provided quantitative data on the precise geometry of the void spaces between the fracture surfaces and the areas of contact at different stresses. At effective stresses of less than 20 MPa fluid flow was proportional to the mean fracture aperture raised to a power greater than 3. As stress was increased, contact area was increased and void spaces become interconnected by small tortuous channels that constitute the principal impediment to fluid flow. At effective stresses higher than 20 MPa, the mean fracture aperture continued to diminish with increasing stress, but this had little effect on flow because the small tortuous flow channels deformed little with increasing stress.
Les resultats d'une etude complète en laboratoire du deplacement mecanique, de la permeabilite, et de la geometrie des vides d'une fracture unique dans un quartz monzonite sont resumes et analyses. Une technique d'injection de metal est presentee, elle fournit des resultats quantitatifs sur l'exacte geometrie des vides compris entre les surfaces de la fracture et les zones d'asperites en contact. Une augmentation de la contrainte effective entraine une diminution non lineaire de l'ouverture moyenne des vides, et une augmentation non lineaire de la surface de contact moyenne. Sous une contrainte effective de moins de 20 MPa, l'ecoulement des fluides est proportionnel à une puissance superieure à trois de l'ouverture moyenne de la fracture. L'augmentation de la contrainte provoque le changement de la surface de contact, les vides deviennent alors relies par d'etroits canaux tortueux qui constituent le principal obstacle à l'ecoulement. Sous une contrainte effective superieure à 20 MPa, l'ouverture moyenne de la fracture continue de diminuer avec l'augmentation de contrainte, cela a peu d'influence sur l'ecoulement parce que les canaux etroits et tortueux se daforment peu quand la contrainte augmente.
Es werden die Ereignisse eines ausfuehrlichen Laborversuchs sur Bestimmung der mechanischen Derschiebung, der Permeabilitat und der Kluftgeometrie einselne Brueche in einem Quars monsonit zusammen gefasst und untersucht. Es wird ein Metalleinspritz-verfahren beschrieben, das in der Lage ist, quantitative Messwerte ueber die genaue Geometrie des Porenraums zwischen den Bruchflachen und unebenen Kontaktflachen zu liefern. Mit effektivem Druck nimmt die Poren-öffuung in nicht linearem Masse ab und die durchschnittliche Kontaktflache in nicht linearem Masse zu. Bei effektiven Spannungen von weniger als 20 MPa fliesst die Fluessigkeit proportionel zur mittleren Poren-öffnung zu einem Exponenten grösser als drei. Mit ansteigendem Druck wird die Anzahl der Flachen in Kontakt verandert und Porenraume werden ueber kleine gewundene Kanale verbunden, welche dss Haupt hindernis fuer die Fluessigkeit bilden. Bei effektiven Spannungen grösser als 20 MPa verringert sich die mittlere Bruch öffnung weiter mit ansteigender Spannung, aber dies hat wenig Einfluss auf den Fluss, weil die gewundenen Kanale nur wenig mit ansteigender Spannung verformt werden.
Fractures, including joints and faults, are a major concern in the geologic isolation of nuclear wastes in low permeability rock. Fractures are the principal conduits along which potentially contaminated groundwater can flow in rock masses with low permeability. Knowledge of the mechanical and hydraulic behavior of fractures in low permeability rock masses is fundamental to the study of nuclear and toxic waste isolation, oil and gas recovery, and fault mechanics. Fluid flow through fractures in low-permeability rocks depends on the state of stress in the rock mass. A fracture can be thought of as two surfaces in partial contact. When a fracture is stressed, the void space deforms and changes in contact area occur, affecting the hydraulic and mechanical properties of the rock. Several researchers have investigated the displacement of fractures and the increase in contact area as functions of applied normal stress. Goodman (1976) measured the deformation of fractured and whole samples and developed an empirical linear relationship between fracture displacement and the logarithm of effective stress. Goodman suggested that the nonlinear behavior of fracture permeability (which depends on aperture) under stress is accounted for by the nonlinear and inelastic behavior of a fracture under compression. Swan (1983) measured fracture surface topography and normal stiffness in slate joints. For certain conditions and assumptions, he observed that hydraulic conductivity, normal stiffness, and true contact area are simple function of pressure and initial aperture and that the surface roughness properties appear to be irrelevant.
