Due to the reduction in frictional resistance, the characteristics of joint infill have a major role to play on rock mass instability. This paper elucidates the laboratory behaviour of graphite infilled joints based on a large-scale shear apparatus under constant normal stiffness (CNS). Discontinuities in a graphite mine have been simulated using high strength gypsum plaster, with the joints infilled with compressed graphite layers. The Fourier series was employed to characterize the joint surface, and the method of using the Fourier coefficients for the prediction of dilation and normal stress with displacement is explained.

Die Charateristik von Verbindungsfuellungen hat einen wichtigen Einfluss auf Felsmassenstabilitat aufgrund der Verringerung des Reibwiderstandes. Diese Veröffentlichung untersucht das Verhalten von Graphit gefuellten Verbindungen im Labormaβstab mit einer Methode die auf einem gross-umfang Apparateprinzip unter konstanter Normal-Steifheit beruht. Unregelmassigkeiten in einer Graphit Mine wurden mit Gypsum Gips von hoher Festigkeit simuliert, die Verbindungen wurden mit kompressierten Graphitschichten gefuellt. Fourier Reihen wurden angewandt um die Verbindungs Flache zu Characterisieren. Die Methode die verwendet wurde um die Ausdehnung und Normalkraft mit der Verschiebung mit Hilfe von Fourierkoeffizienten zu bestimmen wird beschrieben.

Due à diminution des resistances par frottements, les caracteristiques des joints de remplissage joue un rôle majeur sur les instabilites de la roche. Cet article etudie le comportement en laboratoire des joints de remplissage en graphite à partir d'un dispositif de friction à grande echelle sous rigidite normale constante. Les discontinuites dans une mine de graphite ont ete simulees grace à un platre à haute teneur en gypse, dont les joints ont ete remplis de couches de graphite compressees. La caracterisation de la surface des joints a ete realisee avec les series de Fourier. La methode utilisant le coefficient de Fourrier pour la prediction de la dilatation et de la compression en fonction du deplacement est egalement expliquee.


The graphite mines in Sri Lanka are continuously plagued with stability problems. One crucial factor in the evaluation of economic viability of underground graphite mines is the reinforcement cost of unstable underground openings. This instability of jointed walls is common in tunnels as well as in other underground excavations such as stopes, shafts, ore-passes and storage caverns at depths of 500–700m. The main cause of instability is attributed to joints with graphite infill (minor split veins), which branch out from major veins forming unstable rock wedges daylighting to excavations (Figure.1).This study is conducted with the aim of properly understanding their shear behaviour.

Laboratory studies on infilled joints under conventional direct shear (constant normal load) conditions have been carried out by Goodman (1970) and Kanji (1974). The shear strength of rock joints significantly depends on the type of infill and the confinement present in underground conditions. Under such conditions, shearing of rock blocks (unable to deform sufficiently) causes an inevitable increase in the normal stress under Constant Normal Stiffness (CNS). These conditions are more realistic in the simulation of rock joint shear behaviour.

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