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The shear behaviour of infilled joints produced from ordinary gypsum plaster (gyprock) and bentonite was investigated in the laboratory under Constant Normal Stiffness (CNS) conditions. Shear tests were performed on saw-tooth profiles having Joint Roughness Coefficients (JRC) of 4.75 and 9.25 under an initial normal stress (σno) of 0.30 to 1.10 MPa, and at a normal stiffness (kn) of 8.5 kN/mm. Test data under the same σno and infill thickness to asperity height ratio (t/a) were analysed for two different sets of JRC. The peak shear stress plotted against the t/a ratio under constant σno revealed an increase in peak shear stress with the increase in JRC, up to a t/a ratio of about unity. The effect of roughness on the peak shear stress was observed to be minimal when the t/a ratio exceeded 1.40. A mathematical model for the prediction of peak shear stress due to the increased infill thickness has been developed based on a hyperbolic stress-strain relationship and energy balance principles. The model predictions are in good agreement with the laboratory observations. Le comportement de cisaillement des joints remplis produits à partir de platre ordinaire et de bentonite a ete etudie dans le laboratoire sous des conditions de rigidite normales constantes. Des essais de cisaillement ont ete realises sur des profils en dents de scie ayant des coefficients de rugosite des joints (CRJ) variant de 4,75 à 9,25 sous un effort normal initial (σno) de 0,30 à 1,10 MPa, et une rigidite normale (kn) de 8,5 kN/mm. Le resultat des essais conduits sous la même contrainte et epaisseur de remplissage au rapport asperite/hauteur (t/a) ont ete analyses pour deux ensembles differents de CRJ. La variation de l'effort de cisaillement maximal contre le rapport t/a sous une contrainte normale constante a indique une augmentation de l'effort de cisaillement maximal avec l'augmentation du CRJ, jusqu'à un rapport de t/a proche de l'unite. L'effet de la rugosite sur l'effort de cisaillement maximal a ete minimal quand le rapport t/a a excede 1,40. Un modèle mathematique pour la prevision de l'effort de cisaillement maximal dû à l'epaisseur accrue du remplissage des joints a ete developpe sur la base de la variation entre contraintes hyperboliques et deformation et sur des principes de bilan energetique. Das Scherverhalten in mit gewöhnlichem Gips und Bentonit gefuellten Klueften wurde im Labor unter Bedingungen konstanter Normalsteifheit (CNS) untersucht. Scherversuche wurden durchgefuert fuer Sagezahnprofile mit Werten des Fugenrauhigkeitskoeffizienten (JRC) von 4.75 und 9.25 unter Normalspannungs-werten (σno) von 0.30 bis 1.10 MPa, und bei Normalsteifheit (kn) von 8.5 kN/mm. Testresultate fuer gleiche Werte von σno und Verhaltnis Fuelldicke zu Rauhigkeit (t/a) wurden untersucht fuer zwei verschiedene Werte von JRC. Die Beziehung zwischen maximaler Schubspannung und und t/a Verhaltnis unter konstantem σno zeigte einen Anstieg der maximalen Schubspannung mit zunehmendem JRC, bis zu einem t/a Verhaltnis von etwa 1.0. Der Einfluss der Rauhigkeit auf den Maximalwert der Schubspannung war minimal solange das t/a Verhaltnis den Wert von 1.40 ueberstieg. Ein mathematisches Modell wurde entwickelt fuer die Vorhersage der Schubspannung die von zusatzlicher Fuelldicke erwartet werden kann, ausgehend von einer hyperbolischen Spannungs-Dehnung Beziehung und dem Energiegleichgewichtsprinzip. Die Modellvorhersagen zeigten gute Uebereinstimmung mit den Laborbeobachtungen. Introduction Determination of true shear strength of infilled rock joints is imperative in the design of underground structures in jointed rocks, and in the stability analysis of jointed/bedded rock slopes. The presence of clay and silt infill within the rock joints weakens the overall strength of the rock mass. Evaluation of the shear strength of infilled rock joints is usually carried out in the laboratory using the conventional direct shear apparatus, where the normal load is held constant during shearing, i.e., the Constant Normal Load (CNL) method. In the past, CNL tests on infilled joints have been carried out by several researchers including de Toledo & de Freitas (1993), Papaliangas et al. (1993), and Phien-Wej et al. (1990). Non-planar and rough joint surfaces produce significant dilation during shearing (Kodikara & Johnston, 1994; Indraratna et al., 1999; Haberfield & Seidel, 1998). In the field, dilation is partly inhibited by the surrounding rock mass, depending on the magnitude of normal stiffness. Often, the normal stress working on the shear plane increases with the horizontal displacement, hence, cannot be assumed as constant. Such shear behaviour can be described more realistically through shear tests conducted under the Constant Normal Stiffness (CNS) approach.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Mineral > Silicate > Phyllosilicate (0.61)
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. Introduction 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.
- Geology > Mineral > Native Element Mineral > Graphite (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Abstract The deformation monitoring data of the middle pier of the in permanent ship lock in Three Gorges revealed several interesting deformation phenomena. Conclusions and explanations are made concerning the phenomena in this paper, based on the finite element and engineering geology analyses. Firstly, the fluctuation of the horizontal transformations can be attributed to the alternate excavation of the two neighbouring ship lock rooms. Secondly, the rock mass discontinuities result in the displacement breaks. Lastly, the main reasons for the one-sided leaning phenomena are the natural stress, which is not evenly distributed, and the presence of discontinuities. This paper presents a valuable reference for studying the ‘individual phenomena’ in geotechnical engineering. ZUSAMMENFASSUNG Die Beobachtungs claten an der Mittelpier deformation bezueglich Permannenter Schiffsschleuse in den Drei Schluchten offenbaren einige interessante Deformationsphanomene. Die Schlußforgerungen und Erklarungen dazu in dieser Arbeit basseren methodisch anf der ‚' ‘Endlichen-Elemente-Analzse’ und der ‘Ingenieurnissen-Geograhnie- Analzse’. Erstens kann die Fluktuation der horiyontalen Transformation durch die ungleichzeitige Ausgrabung der zwei benachbarten Schiffsschleusenraume verursacht werden. Zweitens resultzert die Diskontinuitat der Felsenmasse ans dem verlagerten Bruch. Drittens: Die Hauptgruende fuer das Zu-einer-Seite-Neigung-Phanomen in manchen Stellen sind der ungleich eigeteilte natuerliche Druck und das vorhandersein der Diskontinuitat. Diese Arbeit prasentiert eine wertvolle Referenz fuer die Untersuchung der Sonderfalle in geotechnischen Bau. Resume Cet article a analyse serieusement et profondement, en utilisant des procèdes d'etude par exemple l'analyse d'elements defini et celle de la condition geographique de traveaux, des règles typiques de la deformation montrees dans les donnees surveillantes à propos de la deformation des pierres centrales dans les ecluses eternelles du Trois Gorges, on en a tire une conclusion:le changement des chiffres des deplacements horizontaux des pierres centrales est cause par les creusages sequentiels des cannelure voisines; l'inclinaison au Nord de toutes les pierres centrales entre les deuxième et troisième chambres d'ecluse est causee par la difference de la gravitation entre les deux chambres d'ecluse et par l'existence de la surface structurale; l'existence de la surface structurale cause le changement des chiffres des deplacements horizontaux des pierres centrales au niveau profond. Cet article donne une reference utile pour l'etude du ‘problème d'indivudualite’ (ou les situations anormaux) dans les donnees surveillantes de la deformation des pierres centrales de la genie civile. Introduction The Three Gorges Project which is under construction on the Yangtze River, China, is one of the largest hydroelectric dam projects in the world. It has posed numerous world-class technological difficulties, among which one of the most challenging is the deformation and safety of the permanent ship lock. The twin 5-flight ship lock is constructed in a deep excavation in granite. The height of the upright sidewall of the lock chamber is 50m in average, with a maximum height of 70m. The width of the bulkhead middle pier is 60m. Direct and credible, inspection has been widely used to evaluate the stability and deformation of rock slopes through measurement of displacement, stress and underground water in the permanent ship lock. The tools for measuring the deep distortion are bore hele clinometers, flex instruments, multipoint extensometers and so on. Inspection instruments are mainly laid at the top of middle masses and road of high slopes. Figure 1 is the sketch map of section 17–17 of the ship lock. In this paper, the section 17–17 and section 20–20 are mainly discussed. Three deformation characteristics have been revealed by the monitoring data during excavation of the ship lock.
- Energy > Renewable > Hydroelectric (0.34)
- Energy > Power Industry > Utilities (0.34)
Physical models from equivalent materials satisfying geometrical and physical similarity have been constructed. A special technology of simulating the excavation of an opening at the front part of a tunnel and of measuring the deformation at the tunnel face was applied. The results yielded by the physical models were used to formulate constitution relations in the numerical solution. This coupled modelling enables us to predict the behaviour of tunnel structures more accurately. On a construit des modèles physiques, realises en materiaux equivalents et repondant aux conditions de ressemblance geometrique et physique. Sur ces modèles, on a utilise une technologie interessante de simulation du forage du tunnel et de la mesure de deformation du front de taille pendant le forage en progression. Les resultats donnes par les modèles physiques ont ete utilises pour formuler les relations de constitution dans la solution numerique. Une telle construction de modèles combines permet de prevoir plus precisement le comportement de la structure du tunnel. Es wurden physikalische Simulierungsmodelle aus aquivalenten Werkstoffen konstruiert, welche die Bedingungen der geometrischen und physikalischen Ähnlichkeiten erfuellen. Bei diesen Modellen hat man die interessante Simulationstechnologie des Tunnelvortriebs sowie die Verformungsmessung beim Tunnelabbaustoβ wahrend des Vortriebsvorgangs eingesetzt. Die Ergebnisse der physikalischen Simulation wurden zur Formulierung von Konstitutionsrelationen in der numerischen Lösung genuetzt. So eine kombinierte Simulation erlaubt eine genauere Prognose des Benehmens der Tunnelstruktur. Introduction Construction of underground structures causes both qualitative and quantitative changes in the rock mass surrounding these structures. The deformation-stress responses of the rock mass can be predicted using either numerical or physical modelling methods. Numerical models are the least expensive tools and allow the user to vary the input parameters flexibly and to obtain results quickly. On the other hand, physical models consist of real and complex simulation of the deformation process in the rock mass, and their results are necessary for correct numerical simulation of the problems under consideration. The most objective results can be achieved by combining both methods. Coupled modelling seems to be the most appropriate and efficient procedure in estimating rock mass behaviour. The study of the stability of a tunnel face, requires determining its deformation and failure in dependence on tunnel driving; experiments on models from physically equivalent materials have been carried out. Based on the results from physical models, the input material properties in the numerical model have been specified. Description of the experiments The experiments are based on the principles of physical modelling. The relationship of the geometrical and physical similarity between model and real states is derived from dimensional analysis (KožešnÍk 1983). In a model stand, dimensions 250 × 250 × 250 mm, a series of physical models was constructed on a scale 1: 100. A lined tunnel of cylindrical shape with an inner diameter of 76 mm and 182 mm in length was excavated parallel to the stand bottom (horizontally). The horizontal axis of the tunnel is positioned at 61.5 mm above the stand bottom symmetrically to the sidewalls of the stand (Figure 1). In the models.