Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Results
ABSTRACT: Viscoplasticity is now regarded as a well established framework for the numerical solutions of plasticity problems. In order to numerically implement viscoplasticity in an efficient way, time step control is essential. The determination of the optimum magnitudes of time steps involves studies of stability and convergence which in turn depend on the failure/yield criterion being used. This work presents such studies in relation to the recent version of Hoek and Brown (Hoek et al.. 1992) failure criterion for intact/fractured rock masses. The details of the criteria used in the definition of the optimum time step are presented. RÉSUMÉ: La viscoplasticitc est vue actuellement cornmc un outil pour la solution numeriquc des problèmes de la Plasticite. En cc que concerne l'implementation numerique de la viscoplasticite d'une manière efficiente. Ie contrôle des intervals de temps est fort important. La determination des magnitudes optimales des intervals de temps prends en consideration les etudes de la stabilite et convergence, lesquelles, a son tour, dependent du critère de rupture/ecoulement employe. Cet article presents les etudes cites ci-dessus par rapport au critere de Hoek et Brown mis à jour (Hoek et al.. 1992) pour les massifs rocheux. ZUSAMMENFASSUNG: Viskoplasrizitat kann als ein gutes etabliertes Rahmenwerk fur die numerische Lösungen von Plastizitatsprobleme geschen worden. Um die numerische Implementierung der Viskoplastizitat leitstungfahig durchzufuehren. Zeitschrittenkontrolle ist wesentlich. Fuer die Bestimmung der besten Amplituden der Zeitschritten. Stabilitat-und Konvergenzanalysen worden durchgefuehrt. Diese Analysen haugen von dern angewandten Fliess und Versagenskriterium ab. Dieser Artikel stellt diese Analysen fuer die neue Version der Hock-Brown Versagenskriterium (Hoek et al.. 1992) fuer anverschrte/geklueftete Felsen von Die Einzelheiten des in der Definition der besten Zeitschritte angenwandien Kriterium werden vorgesfellten. I. INTRODUCTION Most intact rocks behave elastically in the range of stresses experienced in engineering and mining structures. However, in the case of deep mines, the intact rock may yield or fail due to a possible combination of high stresses and fewer joint families. Therefore, in this case, the consideration of rock as an elastic material does not represent the behaviour of this material (Pande et al., 1990) Viscoplasticity is now regarded as a well established framework for the numerical solutions of plasticity problems (Owen et al., 1986) presenting important advantages in the analysis of rock masses: the viscoplastic theory is capable of taking into account the time dependence behaviour of rocks and rock masses and non-associated flow rules and strain-softening features can be trated quite simply In order to numerically implement viscoplasticity in an efficient way, controlling of the time increment is essential In this paper, the study of the computational technique in terms of convergence and stability of the numerical implementation, which, in turn, depend on the failure/yield criterion being used, is emphasized. Such study is presented in relation to the recent version of Hoek-Brown failure criterion for intact/fractured rock masses (Hoek et al., 1992), for its widespread use nowadays. A similar procedure was successfully used in the past for modelling the hydromechanical behaviour of fractured rock masses (Duane, 1994). In a finite element implementation this was done in a self adaptive way, transparent to the user. 2. THE HOEK-BROWN FAILURE CRITERION Among the available failure criteria, Hoek-Brown criterion is the only one to take into consideration the strength of intact and fractured rock masses. Based on published information on intact rock strength, Hoek and Brown (1980a, 1980b) and Hoek (1983) proposed an empirical failure criterion for rock. The following conditions were taken into consideration in the development of their criterion (Hoek et al., 1994).
- Europe (0.68)
- South America > Brazil (0.47)
ABSTRACT: Viscoplasticity is now regarded as a well established framework for the numerical solutions of plasticity problems. In order to numerically implement viscoplasticity in an efficient way, time step control is essential. The determination of the optimum magnitudes of time steps involves studies of stability and convergence which in turn depend on the failure/yield criterion being used. This work presents such studies in relation to the recent version of Hoek and Brown (Hoek et al.. 1992) failure criterion for intact/fractured rock masses. The details of the criteria used in the definition of the optimum time step are presented. RÉSUMÉ: La viscoplasticitc est vue actuellement cornmc un outil pour la solution numeriquc des problèmes de la Plasticite. En cc que concerne l'implementation numerique de la viscoplasticite d'une manière efficiente. Ie contrôle des intervals de temps est fort important. La determination des magnitudes optimales des intervals de temps prends en consideration les etudes de la stabilite et convergence, lesquelles, a son tour, dependent du critère de rupture/ecoulement employe. Cet article presents les etudes cites ci-dessus par rapport au critere de Hoek et Brown mis à jour (Hoek et al.. 1992) pour les massifs rocheux. ZUSAMMENFASSUNG: Viskoplasrizitat kann als ein gutes etabliertes Rahmenwerk fur die numerische Lösungen von Plastizitatsprobleme geschen worden. Um die numerische Implementierung der Viskoplastizitat leitstungfahig durchzufuehren. Zeitschrittenkontrolle ist wesentlich. Fuer die Bestimmung der besten Amplituden der Zeitschritten. Stabilitat-und Konvergenzanalysen worden durchgefuehrt. Diese Analysen haugen von dern angewandten Fliess und Versagenskriterium ab. Dieser Artikel stellt diese Analysen fuer die neue Version der Hock-Brown Versagenskriterium (Hoek et al.. 1992) fuer anverschrte/geklueftete Felsen von Die Einzelheiten des in der Definition der besten Zeitschritte angenwandien Kriterium werden vorgesfellten. I. INTRODUCTION Most intact rocks behave elastically in the range of stresses experienced in engineering and mining structures. However, in the case of deep mines, the intact rock may yield or fail due to a possible combination of high stresses and fewer joint families. Therefore, in this case, the consideration of rock as an elastic material does not represent the behaviour of this material (Pande et al., 1990) Viscoplasticity is now regarded as a well established framework for the numerical solutions of plasticity problems (Owen et al., 1986) presenting important advantages in the analysis of rock masses: the viscoplastic theory is capable of taking into account the time dependence behaviour of rocks and rock masses and non-associated flow rules and strain-softening features can be trated quite simply In order to numerically implement viscoplasticity in an efficient way, controlling of the time increment is essential In this paper, the study of the computational technique in terms of convergence and stability of the numerical implementation, which, in turn, depend on the failure/yield criterion being used, is emphasized. Such study is presented in relation to the recent version of Hoek-Brown failure criterion for intact/fractured rock masses (Hoek et al., 1992), for its widespread use nowadays. A similar procedure was successfully used in the past for modelling the hydromechanical behaviour of fractured rock masses (Duane, 1994). In a finite element implementation this was done in a self adaptive way, transparent to the user. 2. THE HOEK-BROWN FAILURE CRITERION Among the available failure criteria, Hoek-Brown criterion is the only one to take into consideration the strength of intact and fractured rock masses. Based on published information on intact rock strength, Hoek and Brown (1980a, 1980b) and Hoek (1983) proposed an empirical failure criterion for rock. The following conditions were taken into consideration in the development of their criterion (Hoek et al., 1994).
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type (0.98)
On the Use of Artificial Neural Networks As Generic Descriptors of Geomaterial Mechanical Behaviour
Amorosi, A. (Dipartimento di lngegneria Strutturale e Geotecnica, Universita degli Studi di Roma 'La Sapienza'.) | Rampello, S. (Dipartimento di lngegneria Strutturale e Geotecnica, Universita degli Studi di Roma 'La Sapienza'.) | Millar, D.L. (Rock Mechanics Research Croup, Deportment of Earth Resources Engineering, Imperial College of Science, Technology and Medicine)
ABSTRACT: This paper is concerned with the description of the constitutive behaviour of geomaterials of wide ranging character using artificial neural networks (ANNs). The basic idea is to increase the possible options for selection of constitutive models for geotechnical analysis and design through adoption of a neural network representation of the geomaterial constitutive behaviour. First the context of ANNs in this role is presented, followed by a brief description of their operation. Then a general conceptual framework for the use of ANNs for geomaterial constitutive modelling is given and a case study demonstrating the use of the technique for a stiff overconsolidated clay (Vallericca Clay) is presented. Predictions of mechanical behaviour using the ANN are extremely accurate within the stress space explored in the experimental part of the research. The advantages and limits of applicability of the technique are finally discussed. RESUME: Ce papier discute la description du comportement constitutif de geomateriaux à caracterè tres variable, en utilisant des reseaux neroux artificiels (RNA = ANN). L'idee de base est d'augmenter les options disponibles pour la selection de modeles constitutif pour analyse geotechnique et dessein à travers I'adoption d'une representation par reseau neural du comportement constitutif du geomateriel. Premièrernent, Ie contexte des RNAs dans ce rôle est presente, suivi d'une brève description de leur operation. Une assature generale, et conceptuelle pour l'utilisation des RNAs pour modeller constitutivement des geomateriaux est donnee, et ainsi qu'une etude d'un cas demontrant l'untilisation de la technique pour une craie rigids trop consolidee (Vallericca Clay). Les predictions du comportement constitutif utilisant Ie RNA sont extremement precis dans I'espace explore pour Ie stress dans la part experiment ale de la recherche. Les avantages et limites sur I'application de la technique sont discutes. ZUSAMMENFASSUNG: Diese Arbeit handelt ueber die Beschreibung von dem konstitutiven Verhalten von Geomaterialien mit breit gefacherten Charakter unter der Benutzung von kuenstlichen neuralen Netzwerken (artificial neural networks = ANNs). Die Basisidee ist es die möglichen Option fuer die Auswahl von konstitutiven Modellen fur geotechnische Analyse und Design durch die Adoption von einer neuralen Netzwerkreprasentation von dem geomaterialen, mechanischen Verhalten zu verstarken. A1s erstes wird der Zusammenhang von ANNs in dieser Rolle prasentiert, gefolgt von einer kurzen Beschreibung ueber ihre Arbeitsweise Es wird ein generelles konzeptionelles Geruest fuer den Gebrauch von ANNs fur geomateriale konstitutive Modelle gegeben und anhand einer Fallstudie die Benutzung dieser Technik fuer einen steifen ueberkonsolidierten Lehm (Vallericca Clay) demonstriert. Vorhersagen ueber konstitutive Verhaltensweisen unter der Benutzung von ANNs sind ext rem akkurat innerhalb des Spannungbereiches in dem experimentellen Teil dieser Studie. Es werden weiter die Vorteile und Grenzen der Anwendbarkeit dieser Technik diskutiert. 1 INTRODUCTION Figure I schematically shows the relation between primary activities in rock and soil engineering. At the largest scale there is the engineering problem to be solved, that is, the design of the measures to be taken to attain the objective whether it be stabilisation of slopes, securing underground excavations, etc. This activity inevitably leads to some kind of engineering analysis, which involves the use of classification schemes, empirically based analyses, numerical methods, or stability assessment of the overall problem in limit states. Depending on the scope and complexity of the engineering analysis, it is often necessary to undertake a detailed investigation of the mechanical behaviour of the materials at hand, whether they be the natural geomaterials or manmade materials introduced, for example, as structural elements for the purpose of support or reinforcement. Artificial neural networks (ANNs), which are essentially optimisation techniques developed in the computer science discipline, are becoming a part of activities at all of these levels. One example of use at the upper level of the engineering problem, treated as a whole, is the prediction of debris flows occurring as a result of rainfall, where a time series of rain gauge measurements were correlated with debris flow events to produce a debris flow risk indicator (Hirano et al, 1994). Also, ANNs have been used to enhance interpretative aspects of rock mass classification approaches (Millar and Hudson, 1993), and have been employed as indicators of underground opening stability (Feng et at. 1993). This type of application of ANNs in geomechanics lies on the boundary between the level of engineering analysis and the core level which concerns with the mechanical behaviour of geomaterials.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Mineral (0.98)
ABSTRACT: In order to study the influence of particle grain size on the shearing behaviour of rock joints, a series of tilt and shear tests using a model material has been conducted in the laboratory. The average particle size index has been suggested to be the most appropriate parameter to represent the particle size distribution as compared to the geometric mean particle size. It has been found that the joint roughness coefficient, as well as the peak and residual friction angles increase with the average particle size index while the base friction angle does not. However, it has also been shown that the residual friction angle can differ from the base friction angle with increase in the particle size and, in this case the residual friction angle can be expressed as a function of the base friction angle and the average particle size index. RESUME: L'inlluence de la dimension des grains de la roche sur Ie comportement en cisaillement des joints a ete etudie en laboratoire. Deux types d'essais a savoir I'essai de basculement et I'essai de cisaillement en boite ont ete realises sur un materiau synthetique. L'indice moyen de dimension des grains a ete propose comme etant Ie meilleur index pour definir la distribution des grains au sein de la roche, ceci en comparaison avec la moyenne geometrique des grains. Les resultats ont montre que Ie coefficient de rugosite du joint, l' angle de frottement residuel ainsi que l'angle de frottement en pic augmentent avec la dimension moyenne des particules exprimee par I' indice moyen de dimension des grains, tandis que I'angle de frottement de base est independant de ce parametre. L'etude a aussi rnontre que I'angle de frottement residuel peut etre different de I'angle de frottement de base a cause de la dimension des grains. Dans ce cas, il est alors possible d'exprimer I'angle de frottement residuel en fonction de l'angle de frottement de base et de I'indice moyen de dimension des grains. ZUSAMMENFASSUNG: Urn den Einfluß der Partikelkomgröße auf das Scherverhalten von Kluftflachen zu untersuchen, wurde eine Reihe von Neigungs- und Scherversuchen unter Verwendung eines Modellmaterials im Labor ausgefuehrt. Zur Beschreibung der Partikelgrößenverteilung hat sich der mittlere Partikelgrößenindex im Vergleich zu der mittleren geometrischen Partikelgröße, als der geeignetere Parameter erweisen. Experimente haben gezeigt, daß sowohl die Rauhigkeitskoeffizient der Kluftflachen wie auch der Maximum- und Restreibungswinkel mit zunehmendem mittleren Partikelgrößenindex ansteigen, wahrend der Grundreibungswinkel unabhangig vom Index ist. Mit zunehmender Partikelgrößse kann jedoch der Restreibungswinkel von Grundreibungswinkel abweichen, so daß in diesem Fall der Restreibungswinkel als eine Funktion des Grundreibungswinkels und des mittleren Partikelgrößenindex ausgedriikt werden kann. I. INTRODUCTION The behaviour of a rock mass is determined principally by the shear strength of the jointing system, which in turn is influenced predominantly by the roughness of the joint surfaces. The standard shear tests on joints indicate the presence of a peak shear strength followed by the residual shear strength. This behaviour is predominantly due to the dilation that takes place during the displacement due to joint roughness. In rock engineering practice, the design against failure of a potential sliding surface can be accomplished either by use of the Mohr-Coulomb failure criterion, which combines the normal stress with the base friction angle and cohesion in a linear manner, or by using a normal stress dependant empirical law that corrects the base friction angle in order to take account of the microstructure of the sliding surfaces. In this regard, various parameters have been proposed using different approaches to characterise analytically the joint roughness. One can cite the root mean square of the first slope (Myers, 1962); the roughness angle (Patton, 1966); the joint roughness coefficient, (Barton and Choubey, 1978); the fractal dimension (Carr and Warriner, 1987, Tse and Cruden,1979, Lee, 1988, Huang et al 1992); the modified root mean square of the first derivative and the average roughness inclination (Kulatilake et al 1995). All these empirical laws can be expressed in a general form which resembles to the earlier Patton equation (Patton 1966), where r is the strength, a is the norrnal stress,ø is the base friction angle, and i is the roughness angle of the joint.
- North America > United States (0.68)
- Africa (0.47)
ABSTRACT: A method for estimating the peak shear strength of a rock joint in situ is presented. The method is based on a new simple theoretical peak shear strength criterion, which uses a realistic mechanism of shearing and implies that peak shear strength at any normal stress is the result of two components: one purely frictional and one geometrical. For in-situ rock blocks the dilation is negligible and the peak shear strength can be estimated from the frictional component only. RÉSUMÉ: Une methode pour estimer la maximum de resistance au cisaillement des joints de roche in situ est presente. La methode est basee a un nouvel et simple critere theorique de la maximum de resistance au cisaillement, que utilise un mechanisme realiste de fracture et entraine que la resistance maximum en fraction, quel que soit la tension normal, est Ie resultant de deux composants: un purement de frottement et un geometrique. La dilatation est negligeable pour les bloques des roches in situ, et la maximum de resistance au cisaillement peut etre estimer seulement par Ie composant de frottement. ZUSAMMENFASSUNG: Zur Abschatzung der In Situ-Spitzenscherfestikeit vor Ort wird ein Verfahren Vorgestellt, das auf einem neuen, einfachen theoretischen Kriterium basiert. Das Kriterium macht von einem realistischen Mechanismus der Sherkraft in Gesteinen Gebrauch, nach dem die Spitzenscherfestikeit einer Gesteinkluft unter Normaldruck aus zwei Komponenten besteht: einer Reibungskomponente und einer geometrischen Komponente. Bei Gesteinformationen ist die geometrische Komponente vernachlassigbar und die Spitzenscherfestikeit lasst sich alIein durch die Reibungskomponente abschatzen I. INTRODUCTION A new simple theoretical peak shear strength for rock joints has been recently proposed by Papaliangas et al, (1995). According to the new criterion, the peak friction angle of a rock joint can be considered as a two-component quantity: a) a purely frictional (independent of normal stress) component øm due to shearing of the rock wall material and b) a dilational component µ, due to the surface roughness. friction angle arises from the shear strength of rock junctions, formed under normal stress sufficiently high to cause plastic deformation of the contacting asperities, as anticipated from the adhesion theory (Bowden & Tabor, 1950). This occurs when the true normal stress approaches the brittle-plastic transition stress and therefore, øm can be determined from triaxial tests at confining pressure of this magnitude (Figure 1). The brittle plastic transition stress may be higher or lower than the unconfined compressive strength. Some strong rocks, such as granites, may have a transition pressure as high as five times the unconfined compressive strength or higher, whereas limestones and marbles may have a transition pressure lowerthan the unconfined compressive strength (Mogi, 1966, Paterson, 1978). Byerlee (1978) found that mineralogy has little or no effect on the friction angle of rocks, but Mogi (1966) calculated friction angles for carbonate rocks which were markedly higher than those of silicate rocks. From an analysis of published experimental data, it appears that typical values for øm for natural, rough joints in fresh rock are about 39° for silicates and a few degrees higher for carbonates. Therefore, if the dilation is zero, the peak friction angle will be equal to øm which represents a lower bound. This lower bound, which is considerably higher than the friction angle obtained from saw-cut surfaces, is in agreement with most experimental results, where a lower bound of this magnitude is observed in most direct shear tests. Two examples of such results taken from Baldovin (1970) and Giani (1992) are shown in Figure 2. If the joint is filled with sandy or clayey material, both the dilational and frictional characteristics are altered (Papaliangas et aI., 1990 and 1993).
- Europe (1.00)
- North America > United States (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.55)
ABSTRACT: The results of a study on the influence of the joint roughness, considered to be a geometric parameter only, on the evaluation of the shear strength of the two making surfaces are presented. Reference is made to casts of natural discontinuities in order to carry out a number of shear tests with increasing normal stress on surfaces with the same roughness, thus avoiding the problem of altering the initial discontinuity roughness during the test. A good agreement was found between the values of the second order angles i (Patton, 1966), that were measured with an automatic mechanical profilometer, the values of the angles of first displacement ß obtained from a tilt test, and the values of i=arctg(µ/O)-øb obtained from direct shear tests. This allows one to write a relation between the value of the angles i, measured by the mechanical profilometer, and the horizontal strain given by the percentage of the relative displacement of the two surfaces of a discontinuity. In this manner a reliable prediction can be made in an early stage of the analysis, when only the data on the discontinuity morphology and the tilt test results are available. RESUME: On va presenter les resultats d'un etude sur I'influence de la rugosite, entendu seulement comme parametre geometrique, dans la determination de la resistance au cisaillement des discontinuites. L'etude a etee effectuee en utilisant des calques de discontinuites naturelles. Ca à fin que I'application des efforts normals croissants Sur des surfaces du meme type n abîme pas la rugosite naturelle. On a obtenu une bonne correspondance entre les valeurs des angles i de deuxieme ordre (Patton 1966), que I'on a mesure avec un appareil automatique, les valeurs des angles de deplacement initial ß obtenues des Tilt-tests et les valeurs de i=[arctg(t/o) -ø,b] obtenues des essais de cisaillement directe. Ca a permis, dejà dans une première phase, limitee aux leves de rugosite avec appareil automatique et mesures de Tilt-tests, de proposer une relation synthetique entre les valeurs du parametre i mesurees et la deformation horizontal exprimee comme pourcentage du deplacement relatif des deux surface de la discontinuite. ZUSAMMENFASSUNG: Die Untersuchungen beziehen sich auf den Einfluss der rein geometrisch zu betrachtenden Rauhigkeit bei der Bestimmung des Gleit-Wiederstandes zwischen angelehnten Flachen. Die Untersuchungen wurden mit Abdruecken natuerlicher Diskontinuitaten durchgefuehrt, damit durch die Scherversuche mit zuhnemenden normalen Druck auf gleichen Flachen die urspruengliche Rauhigkeit der Oberflache nicht verandert wird. Es konnte eine gute Übereinstimmung zwischen den mit authomatischen Prophilograph gemessenen i Winkeln des zweiten Grades (Patton 1966), den mit "tilt tests" erhaltenen Warden der rested Verschiebungswinkeln ß und den mit direkten Scherversuchen erhaltenen i = {arct(t/o)-ø,b] Werte, festgestellt werden. Somit ergibtsich die Möglichkeit schon in der rested Phase der Untersuchungen, bzw. wahrend der Rauhigkeit Aufnahme und der "tilt tests" Messungen, voraussichtlich eine synthetische Relation zwischen den mit Prophilograph gemessenen i Winkel-Werten und der als prozentualische Flachen Verschiebung ausgewerteten horizontalen Verformung, Vorzuschlagen. 1. INTRODUCTION When the two surfaces of an unfilled discontinuity are sheared, the mobilised shear strength is given by the contribution of various factors, which are at first assumed to be independent of each other. These factors are: - the roughness of the two surfaces; - the percentage of imposed strain; - the applied normal stress; and - the intact rock strength. As the displacement increases, the geometry of the initial interlocking condition between the two surfaces is modified (i.e. the area and the morphology of the surfaces in contact). Moreover, in relation to the applied normal stress, both the roughness of the surfaces and the initial characteristics of the intact rock may change. As a consequence, after shearing starts the various factors can no longer be considered to be independent of each other.
ABSTRACT: The thermal conductivity of quartz-illite and smectitic shales is being investigated as a function of temperature, stress, pore pressure, and bedding anisotropy. Experiments are performed using the Waterloo Thermal Conductivity Cell: a one-dimensional, steady state, heat flow device. The use of optical quartz as a standard will ensure a reliable calibration factor for the cell. The effective thermal conductivity of the cell has been determined for temperatures 25–85°C. These values are used in the calculation of thermal conductivity for various shale samples and will eliminate the contact resistance formed between the sample and the cell. Preliminary results for the Queenston shale indicate slightly higher values for thermal conductivity (1.74 - 1.82 Wm-1K-1) than the currently accepted range for shales (1.05 - 1.45 Wm·-1K-1). This is attributed to the high muscovite and quartz Content of the Queenston shale. Resume: La conductivite thermique de quartz-illite et de schistes argileux smectiques en fonction de la temperature, de la tension, de la pression interstitielle et de l' anisotropie de la stratification est a. l/etude, Les experiences sont conduites dans la cellule de conductivite thermique Waterloo; un appareil à flux thermique uni-dimensionnel regularise, L'utilisation de quartz optique com me norme assurera un facteur de calibration de la celIule fiable. La conductive thermique reelle de la cellule a ete determinee pour des temperatures de 25–85°C. Ces valeurs sont utilisees dans Ie calcul de la conductivite thermique de divers echantillons de schistes argileux et elimineront la resistance de contact entre l'echantillon er la cellule. Les resultats preliminaires sur des schistes argileux de Queenston donnent des valeurs de conductivite thermique legerement superieures (1.74–1.82 W-1K-1) aux valeurs couramment obtenues pour des schistes argileux (1.05–1.45 Wm-1K-1). Cet ecart est auribue à la forte teneur en muscovite et en quartz des schistes argileux de Queenston. ZUSAMMENFASSUNG: Die Warmeleitfahigkeiten von Quarz-Illite und Srncktitischen Schiefer sind in Abhangigkeit von Temperatur, Spannungszustand, Porendruck und Bettanisotropie untersucht worden. Die Experimente sind mit der Waterloo Thermal Conductivity Cell durchgefuehrt worden - einem Gerat zur eindimensionalen Warmesuornmessung im Beharrungszustand. Optischer Quarz ist zur zuverlassigen Kalibrierung der Zelle benutzt worden. Die effektive Warmeleitfahigkeit der Zelle ist fuer Temperaturen von 25°C bis 85°C bestimmt worden. Diese Werte werden in den Berechnungen zur Bestimmung der Warmeleilfahigkeit verschiedener Schieferproben benutzt, um den durch den Warmeleitwiderstand an der kontaktstelle zwischen Zelle und Probe verursachten Fehler zu eliminieren. Vorlaufige Ergebnisse fuer den ‘Queenston’ Schiefer weisen leicht höhere Werte fuer die Warmeleitfahigkeit auf (1.74 - 1.82 W-1K-1) im Vergleich zu dem allgemein akzeptierten Bereich fuer Schiefer (1.05 - 1.45 Wm-1K-1). Dies ist auf den höheren Muskovit-und Quarzgehalt des ‘Queenston’ Schiefers zurueckzufuehren. 1 INTRODUCTION to the thermal history and organic maturation in these basins. It has been suggested (Blackwell and Steele, 1989) that laboratory measurements of shale thermal conductivities are unreliable and 25–50% lower than literature values. The thermal conductivity of shale may change unpredictably during deformation. It is, therefore, important to the thermal history of sedimentary basins and how this affects the maturation of the basin is of particular interest to petroleum geologists and engineers. The thermal conductivity is of particular interest so that modelling techniques can be applied determine the thermal conductivity of individual shales and how they behave during the deformation process. 2 BACKOROUND The transfer of heat is one of the fundamental processes involved with the first law of thermodynamics. The first law equation for a closed system.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Mineral > Silicate > Tectosilicate > Quartz (1.00)
ABSTRACT: Roughness performs a dominant role in the mechanical and hydraulic behaviour of rock joints, but no method exists to completely describe it. This paper presents the work done for digitisation of 10 joint samples, a statistical study of the asperity heights, a review of the roughness indices and the calculation of some indices and of the fractal dimension of the joints. Correlations with JRC were established and critically analysed. RESUME: La rugosite joue un rôle dominant dans Ie comportement mecanique et hydraulique des joints rocheux, mais aucun methode peut la decrire completement. Cette communication presente Ie travail fait pour la digitalisation de 10joints, un etude statistique des asperites, une revision des indices de rugosite et Ie calcul de quelques indices et de la dimension fractale des joints. Des correlations avec JRC ont ete etablies et sont critiquement analisees. ZUSAMMENFASSUNG: Rauhigkeit spielt eine beherrschende Rolle im mechanischen und hydaulischen Verhalten von geklueftetern Fels, aber es existiert kein Verfahren um sie vollstandig zu beschreiben. Der vorliegende Bericht stellt die Arbeit der Digitalisierung von 10 Rissen dar, eine statistische Untersuchung der Rauhigkeit, eine Übersicht der Rauhigkeitsindexe, sowie die Berechnung einiger Indexe und der Fraktaldimension der Exemplare. Korrelationen mit JRC wurden hergestellt und kritisch analysiert. I. INTRODUCTION In fractured rock masses, the mechanical and the hydraulic properties are influenced to a large extent by the presence of the joints. In order to understand this decisive role of the joints it is important to study the basic properties of the individual joints, which are intimately linked to their geometry. One of the main geometrical properties of individual joints, which is recognized to perform a relevant role in their hydraulic and mechanical behaviour is roughness. Roughness of rock joints is, however, a property difficult to define and to quantify, because there are no measurable quantities that can completely describe it. In the work reported in this paper several methods were used for quantification of roughness, based on the surface topography of natural joints, and the results obtained are presented and analysed. This research is part of a doctoral thesis (Lamas, 1993) concerned with the hydro mechanical behaviour or jointed rock masses. For the geometrical characterization of individual joints, 10 samples (labelled A01 to A10) of granite joints of the Alto Lindoso hydro-electric power scheme, located on the river Lima, in the North of Portugal, were studied in laboratory. The samples were collected in the zone of the powerhouse complex, at a depth of 340 m. They are cylinders with the joint in the axial position, the dimensions of the joint being 102 mm × 51 mm. The grain of the granite in samples A0I to A06 is slightly coarser (2 to 4 mm) than in samples A07 to AI0 (2 to 3 mm). The joint surfaces are little to moderately weathered and show no sign of previous shearing. Previous results of uniaxial compression tests on this rock gave mean values of the Young's modulus. Poisson's ratio and uniaxial compressive strength of E=60GPa, v=0.2 and µ= 140MPa respectively, and the results of joint shear tests in joint samples gave mean values of the friction angle and apparent cohesion of Coulomb's model of ø = 37° and c = 0.08 MPa. 2. JOINT PROFILING For the study of joint surface topography it is necessary to determine the heights of the asperities with respect to a reference plane. Ideally, the sampling process should be uniform in the whole surface. In the present work, however, it was considered reasonable to obtain several linear profiles along the axial direction of the samples.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Igneous Rock > Granite (0.81)
ABSTRACT: Results of different laboratory tests conducted in well preserved downhole shales show that it is actually water within the shale (amount and distribution), rather than air, that controls shale reaction when the rock is in contact with water solutions. When shale is dried without introducing air into the rock, it reacts exactly the same way as if drying was done while exposed to air. Shale reaction is only observed when the original water content is somehow modified. Type of reaction varies according to both amount and distribution of the water remaining within the sample. Bound water redistribution indicates that shale dryness may not be a reversible process. Research also shows that mechanical damage changes water content and, therefore, shale reaction. Practical implications on shale preservation, laboratory testing, and well bore stability are discussed. RÉSUMÉ: Les resultats de divers experiences conduites sur des carottes prelevee en fond de puits et bien preservees montrent que c'est en verite I'eau retenue (quantite et repartition) par les mineraux, et non l'air, qui gouveme la reaction du schiste au contact des solutions aqueuses. Quand le schiste est deshydrate a I'abris de l'air, il reagit au contact de l'eau exactement de la même maniere que s'il avait ete seche a l'air. La reaction du schiste a eu lieu seulement lorsque sa teneur en eau originale est modifie d'une manière ou d'une autre. Le type de reaction varie selon la quantite et repartition de I'eau retenue par l'echantillon. La redistribution de l'eau intra-agrègat indique que la deshydration du schiste peut-être pas un procède reversible. Cet article montre aussi que Ie dommage mechanique change la teneur en eau et par consequent la reaction du schiste. Les implications pratiques sur la preservation du schiste argileux, essais de laboratoire, et la stabilitè de forage sont discutèes. ZUSAMMENFASSUNG: Verschiedene Labortests wurden in gut erhaltenen Tonschiefem des Liegenden durchgefuehrt. Die Resultate zeigen, daß eigentlich die Menge und die Verteilung des Wassers im Tonschiefer die Reaktion kontrolliert, wenn dieser in Kontakt mit einer wassrigen Lösung gelangt. Die Luft in der Probe hat dabei eine geringere Bedeutung. Wenn der Tonschiefer getrocknet wird ohne das Luft in sein Inneres gelangt, dann verhalt er sich genau so, als ob er unter Luft getrocknet wurde. Eine Reaktion des Tonschiefers wurde nur beobachtet, wenn der urspruengliche Wassergehalt modifiziert wurde. Der Reaktionstyp variiert abhangig von der Menge und von der Verteilung des restlichen Wassers in der Probe. Eine Umverteilung des gebundenen Wassers zeigt an, daß die Trockenheit des Tonschiefers ein nicht umkehrbarer Prozess sein kann. Der Artikel zeigt auch, daß mechanische Zerstörung den Wassergehalt und die Reaktion des Tonschiefers verandert. Praktische Auswirkungen auf die Erhaltung des Tonschiefers, sein Verhalten wahrend Labortests und die Bohrlochstabilitat werden diskutiert. 1 INTRODUCTION shale and water composition (Chenevert, 1970; Sherwood, 1992; Slade et al., 1991; Yew et al., 1990). Research in the past was, therefore, directed towards selecting proper additives and solution compositions to avoid shale reaction and swelling (O'Brien & Chenevert, 1973; Steiger, 1981; Bol, 1986). In the past, no attention was paid to preserving the original water content of samples used in When drilling oil/gas wells with water-based muds (WBM), shale hydration and swelling has long been blamed for the majority of instability problems faced. It is well known that when a shale is in contact with a water solution some ion exchange occurs and the rock absorbs water. Therefore, the shale swells and becomes weaker. This reaction is a function of laboratory tests. Consequently, many results and conclusions obtained from tests were derived from dried or partially dried shales. A few years ago it was observed that partially dried shale behaves differently from saturated shale Presence of air inside the rock was thought to be the main cause, generating capillary effects that lead to shale swelling (Schmitt et al., 1994; Forsans & Schmitt, 1994; Onaisi et al., 1994). The idea, then, became to use saturated samples in laboratory tests, eliminating the air inside the rock. Procedures to resaturate partially dried shale samples were developed and are now in use in different institutions.
- South America > Brazil (0.69)
- North America > United States > Oklahoma (0.28)
ABSTRACT: Drilling with water based fluids often results in borehole stability problems in shale sections. Such effects are often assumed to be related to chemical interactions between the drilling fluid and the shale. Laboratory experiments have been conducted to study the effect of different brines on the mechanical properties of shale. A North Sea Tertiary shale has been exposed to various concentrations of KCI- and CaCl2- brines under different conditions of pressure and temperature. Exposure to KCI-brine under realistic downhole conditions with respect to temperature and pressure was seen to cause shrinkage and reduced stiffness, while exposure to CaCI2-brine caused no deformation and no change in stiffness. Comparing with results from testing under atmospheric conditions, it is obvious that evaluation of shale response based on atmospheric tests alone may be misleading. RÉSUMÉ: Lutilisation de fluides de forage a base d'eau mène souvent a des problèmes de stabilite des parois lors du forage à travers des formations argileuses et argiliteuses. Ces difficultes sont supposees provenir d'interactions chimiques entre Ie fluide de forage et les argiles. Des experimentations en laboratoire ont permis d'etudier I'effet de differentes saumures entrant dans la composition des fluides de forage, sur les proprietes mecaniques d'une argilite. Une argilite du Tertiaire de la Mer du Nord a ete exposee à des saumures contenant des concentrations variables de KCl et CaCl2 sous differentes conditions de temperature et pression. L'exposition dans des conditions representatives des conditions de fond à des saumures riches en chlorure de potassium (KCI) entraîne une contraction du materiau et une diminution de sa rigidite, alors qu'une exposition à des saumures riches en chlorure de calcium (CaCI2) n'entraîne ni deformation ni variation de rigidite. Enfin il est mis en evidence que les mêmes tests realises en conditions atmospheriques ne fournissent pas les mêmes resultats. ZUSAMMENFASSUNG: Der Gebrauch wasserbasierter Bohrspuelungen fuehrt in Schiefertonabfolgen oft zu Stabilitatsproblemen im Bohrloch. Oft wird angenommen, daß solche Effekte mit chemischen Wechselwirkungen zwischen der Spuelungsfluessigkeit und dem Schieferton zusammenhangen. Um den Einfluß verschiedener Salzlösungen auf die mechanischen Eigenschaften von Schieferton zu untersuchen, wurden Laborexperimente durchgefuehrt. Ein tertiarer Schieferton aus der Nordsee wurde KCl- und CaCI2- Lösungen verschiedener Konzentrationen unter verschiedenen Druck- und Temperaturbedingungen ausgesetzt. Unter realistischen Bohrlochbedingungen in bezug auf Temperatur und Druck fuehrte die Einwirkung von KCI-Sole zu Schrumpfung und verringerter Steifheit, wahrend CaCl2-Sole weder Deformation hervorrief noch die Steifheit beeinflußte. Der Vergleich mit Ergebnissen von unter atmospharischen Bedingungen durchgefuehrten Versuchen macht offenbar, daß die Beurteilung des Verhaltens von Schiefertonen ausschließlich auf der Basis atmospharischer Tests zu irrefuehrenden Schlußfolgerungen fuehren kann. 1 INTRODUCTION In drilling for oil and gas, oil-based (or pseudo-oil based) drilling mud has proven to be superior with respect to drilling performance in shales. Use of oil-based mud implies a fluid system consisting of two non-mixable phases; the in-situ formation water in the shale and the oil-based mud in the well. Because the pore radius in down hole shale is normally less than I µm, and the shale is typically water-wet, quite large capillary entry pressures occur, and this helps establish an effective mud support to the formation. This is one of the reasons for the success of oil-based mud in shales. With the use of water-based mud, this two-phase support does not exist. However, environmental restrictions has forced the oil industry to change to water-based muds. This has led to more borehole stability problems during drilling of problematic shale sections, and therefore also a need for better understanding of the physical and chemical mechanisms going on between the shale and the water-based fluids. 2 SHALE-FLUID INTERACTION PROCESSES Shales consist of large amounts of clay minerals which are quite sensitive to the electric character of the water. This may result in different mechanical behaviour of the shale depending on the salinity of the water and which type of ions or polar molecules are present. During the period when the shale is exposed to the mud, transport of water and/or ions may take place, both into and out of the formation. The extremely low permeability together with the electrical sensitivity of the shales result in different transport rates for the different constituents within the formation water and the water-based muds, and therefore transient changes in the mechanical behaviour can occur. The extreme limit will be pure osmosis, when only water molecules can pass through the borehole surface and are driven by a chemical potential gradient. In this situation, the result would be a change in pore pressure and the effective stress.