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SUMMARY: The paper refers to the stability analysis for underground cavities of large cross section, which are to be constructed either without or with minimum lining. Since such cavities may only be constructed in favorable engineering-geologically conditions, i.e. in hard rock masses, their stability is influenced mostly by the number, configuration and characteristics, as well as by latent discontinuities of fissures. The proposed procedure makes it possible to identify the safety factor for each monolith, which is a fundamental condition for establishing of the number, magnitude and direction of the anchors in the underground cavity. The procedure enables us to choose the best location, orientation, size and shape of the underground cavity. RESUME: Cet ouvrage se refère à l'analyse de la stabilite des cavites souterraines de grande section transversale que l'on construit soit sans soit avec le revêtement minime. Ces cavites ne pouvant être construites que dans les conditions ingenieurs-geologiques favorables, c'est-à-dire dans les roches en place solides, leur stabilite est la plupart du temps influencee par le nombre, la configuration et les caracteristiques des fissures, ainsi que par les discontinuites latentes. Ce procede nous permet de determiner le facteur de stabilite des monolythes; tout ceci sert de base pour la determination du nombre et de la position des ancres dans une cavite souterraine. Ce procede rend possible de determiner la meilleure localization, orientation, forme et grandeur de la cavite souterraine. ZUSAMMENFASSUNG: Dieses Werk bezieht sich auf die Stabilitatsanalyse der grossen unterirdischen Hallen, die konstruiert mit oder ohne leichtberg Gesicherung sind. Nachdem diese Raume nur unter den guenstigen ingenieur-geologischen Bedingungen konstruiert sein können, das heisst in den soliden Felsenmassen, ihre Stabilitat ist am meistens bei der Zahle, der Forme und bei den karakteristischen Fugen der der Diskontinuitaten beeinflusst worden. Diese Methode macht uns möglich den Sicherheitssgrad der vershiedenen Monolythen festzustellen, unci dies könnte auch als die Unterlage fuer die Bestimmung der Zahle und der Verteilung der Anker in einer unterirdische Halle dienen. Dieses Verfahren ermöglichst die Feststellung der besten Orientierung. Ort, Form und Grösse der unterirdische Halle. The engineering-geological structure of sites in Yugoslavia often calls for the construction of undergroung works in hard rock masses With lithologically or tectonically predisposed fissures. The paper presents an attempt to find a simple procedure to get the prior information on the degree of monolith's stability in the zone around the opening of an artificial underground cavity. The work analyzes the stability of monoliths around circular underground cavity's section (Fig.1). The starting points of the analysis are the following: - Sliding commences when at each point on the sliding surface the shear stress τ, inducted by external forces, reaches the shear strength at that surface. - Stresses in the rock mass around the tunnel opening of circular cross section are determined in the same way as for a homogeneous, isotropic and elastic medium - The rock mass is in the plane strain state. The basic steps in the procedure are the following: - The first step is to define the state of stress around the underground cavity, what enables us to determine the forces acting on monoliths. - The second step is to analyse sliding stability of monoliths alongside the surfaces of discontinuities. Normal forces and tangential forces acting on monoliths are the resultants of the corresponding stresses б n, б n and бe /equations (7).... (11)/. Knowing normal forces and tangential forces, we examine the stability of monoliths alongside the surfaces of discontinuities. This procedure will be shown on a monolith M (Fig.5). As the result of the shear strength of surfaces A3 and A4, it comes to the increasing of the partial safety factors, i.e. we are getting the global safety factors. We obtain the condition that the global safety factors for sliding of monolith M, alongside the sliding surfaces Al and A2 are equal one to another, i.e. This procedure may be the basis for the analysing the stability of monoliths when in the rock mass there is the three dimensional state and in the case when the underground cavity has not only the circular cross section, but has different cross sections. In that case the most difficult problem is to determine the stresses, i.e. forces acting on monoliths. In those cases we may use the finite element method. This procedure put us in the way of obtaining information about the stability of the monoliths around a planned underground cavity, provided that the structure of the fissured medium and the shear strength characteristics at the relevant contact surfaces are known. In such a way we may obtain an advantageous location of the underground cavity connected to that geotechnical aspect. We may determinate the number, magnitude and direction of anchors, if they are necessary, and the best directions for pressure groundings, too.
SUMMARY: Analysis of slopes stability for weathered crystalline rocks like the schists of Caracas necessitates an approach distinct from procedures routinely applicable to hard, fractured rocks, on the one hand, or soils, on the other hand. Neither of the latter two materials can generally sustain tensile stresses whereas decomposed rocks often can. In order to examine the effects on stability of having tensile stresses within the upper part of a slope, a new concept of inter-slice forces is introduced such that both compressive and tensile forces are included. For the equilibrium analysis of steep slopes with simple morphology, an analytical solution was obtained. For more general cases, numerical procedures were adopted. Finally a method is suggested whereby one can calculate the depth and location of tensile cracks for rocks in different stages of weathering. RESUME: Le problème de la stabilite des pentes en roches crystallines decomposees ayant une certaine resistance à la traction doit être envisager d'une façon differente de comme on le resout normalement quand il s'agit, dit-on, de roches dures fracturees ou de sols non coherents. On introduit ici un nouveau concept sur les forces qui agissent sur les plans verticaux de la pente, de façon à permettre d'avoir au même temps des efforts en traction et en compression le long d'une ligne. À partir de cette hypothèse, la solution des equations d'equilibre statique permet d'obtenir les valeurs des forces autour d'un element trapezoidal et, par consequant, la position des crevasses la où les efforts en traction atteigneut une certaine limite. ZUSAMMENFASSUNG: Wenn man die Abhang-Stabilitat von gewitterten krystallischen Gestein (zum Beispiel Caracas Schist) analysieren will, braucht man eine Betrachtungsweise die von normalen Vorgehen, geignet einerseits fuer zerklueftetes Gestein und andererseits fuer Erde, abgesondered ist. Allgemeinlich können keine von diesen zwei Materialen Zugspannung wiederstehen, wahrend verwestetes Gestein es öfters kann. Um die Effecten der Zugspannung in der höheren Halfte des Abhangs untersuchen zu können, ein neuer Begriff ist aufgebracht, det mit zwischen-scheibigen Kraften verkehrt, so dass beide Druckund Zugkrafte eingeschlossen sind. Eine analytische Lösung war erreicht fur die Gleichgewichtanalyse von steilen Abhangen mit einfacher Morphologie. Fuer rnehr allgeimeine Falle eine numerische Arbeitsweise war angenommen. 1. INTRODUCTION This paper describes a procedure for evaluating the stability of steep natural and cut slopes in weathered rocks, based upon the analytical solution to a system of differential equations of static equilibrium for a connected, sliding body. The elements on Which the analyses are carried out are similar to the "Slices" commonly used in a limit equilibrium analysis, except that tensile as well as compressive stresses are considered along the vertical sections. The investigations which have led to the results presented here are an outgrowth of civil engineering experiences in Colombia and Venezuela. In these tropical countries, landslides in weathered rocks have been analyzed using, as appropriate, either soil mechanics methods, e.g., the method of slices, or rock mechanics approaches, e.g., wedge analysis. The results suggested that something else was needed for the steep slopes of partly decomposed rocks. Soil mechanics methods are usually used where slopes are less than about 30 degrees and the materials can be assumed to lack tensile strength. Under such conditions, procedures developed by Bishop (1955) and Morgenstern and Price (1965) have given satisfactory and dependable results [Whitman and Bailey (1967); Wright et. al. (1973)]. Methods used for analysis of rigid block slides on planar discontinuities in hard rocks are also invaluable, e.g., methods discussed by Wittke (1965), John (1970), Londe et. al. (1969, 1970), and others. But neither approach offers a model suitable for analysis of a slope cut steeper than 45 degrees which remains stable for a few decades or less and then develops a deep tension crack, finally collapsing by sliding along a curved slip surface. Yet this is precisely what occurs time and again in weathered rocks. Gradual loss of strength ·in rock due to natural or induced weathering and its physical and economical consequences is especially important in countries with a tropical or subtropical climate characterized by mild to warm temperatures and abundant rainfall. Landslides induced by weathering of the rock in such countries are described by Morgenstern (1978) for Hong Kong and Brazil and by Riddolls (1974), Millar (1974), and Brown (1974) for New Zealand. In most cases, tension cracks in the upper part of the slope were conspicuous even for an inclination of the face as low as 45 degrees. Though intended primarily to fill a need of engineering in tropical countries, the analysis to be discussed here should also have application in temperate regions. For example, as long ago as 1846, Alexander Collin discussed progressive destruction of cohesion of rocks through weathering in France; he observed that cracks developed in the early stage of a landslide and subsequently extended to join the upper part of the slip surface.
- South America > Venezuela > Capital District > Caracas (0.46)
- North America > United States > California (0.29)
- Asia > China > Hong Kong (0.24)
SUMMARY: In this paper, first, the method of a complex variable taking time dependency and anisotropy of the ground into consideration is newly proposed to estimate surface displacements caused by shallow tunnel driving in soft ground subject to gravity. Secondly, theoretically calculated values are shown to have good agreements with field data. ZUSAMMENFASSUNG: Die oberflachlichen Verschiebungen verursacht durch den Graben des Tunnels in einem anisotropen viskoelastischen Grund werden durch das Berechnungsverfahren der komplexen Veranderlichen gelöst. Dann werden die Feldmessungen mit den theoretischen Resultaten verglichen. SOMMAIRE: Cel article analyse les tassements superficiels induits par le creusement d'un tunnel à faible profondeur dans un sol mou soumis à son poids propre par une methode faisant appel au domaine complexe et incluant les effets de fluage et d'anisotropie du sol. Finalement, plusieurs mesures Sur le terrain sont comparees aux predictions theoriques. INTRODUCTION The excavation of a shallow tunnel in soft ground brings about surface displacements of the ground. Therefore, it may be required, in advance, to estimate the magnitude of surface displacements and their effects on neighboring structures. As surface displacements are affected not only by such geometrical conditions as the depth of burial for a tunnel and inclination of ground surface but also by several geological properties, little information has been available up to now about the accurate estimate of the magnitude of the displacements. It is of importance to take into account the fact with respect to deformation phenomena that the surface displacements over a tunnel in soft ground generally increase with time and are affected, in no small quantities, by directions of sedimentation, stratification and joints which bring out the anisotropic properties of the ground as a whole. In this paper, problems of surface displacements resulting from shallow tunnel driving in soft ground subject to gravity are analyzed by the method of a complex variable, considering time dependency and anisotropy of the ground. Subsequently, the results of several field measurements with respect to displacements are compared with the theoretical ones. METHOD OF ANALYSIS 1. Fundamental relationships for an anisotropicelasticity The authors refer the ground to Cartesian coordinate system (X1,X2,X3) shown in Fig.l. 2. Determination of stress functions The tunnel excavation can be expressed by releasing the initial stresses σijnj which exist on the virtual tunnel boundary B1(Fig.1) before the excavation, where nj are the components of the inward unit vector normal to B1. The initial stresses can be considered as functions of parameter θ having period 2π, and they can be expanded in Fourier series in cos (mθ) and sin(mθ). The expressions of the infinite series on the right-side of the above equations are obtained as a result of the integration of the,initial stresses with respect to arc-length along the contour B1. Then the coefficients bjk (m) become known complex quantities. On the other hand, 1bjo must be determined by the condition that the displacements caused by the tunnel excavation must be equal to zero at infinity. 3. Initial stresses of the ground due to gravity Initial stresses in the anisotropic elastic ground due to gravity can be obtained by considering such conditions:All of the stresses σij are independent of the X1-axis. σ22=0, 012=0, 02,=0 on B2. Strain E11 is caused by σ11 only, which is the normal stress component obtained from equilibrium equations with respect to gravity. ε13=0 in the ground. ε33=0 in the ground. 4. Displacements caused by tunnel excavation in anisotropic viscoelastic ground These equations independent of time correspond to those of anisotropic elastic ground. It has been shown that the way to solve boundary value problems in the theory of viscoelasticity is to apply the Laplace transform, with respect to time, to the time dependent field equations and the boundary conditions. By so doing, the solution to the original problem is reduced to the transform inverse of a solution to the transformed problem. 1. Convergent characteristics of analytical functions Fig.2 shows convergent characteristics of the analytical functions. It may be recognized that the convergent characteristics of analytical functions are fairly good and that if the first two terms of the infinite series of the functions are used, engineering accuracy will be satisfied. In the following analysis the first four terms of the infinite series are used. 2. Analytical results The horizontal and vertical displacements (Uh and Uv respectively) of ground surface are summarized in Figs.3 and 4. From Fig.3 we can see that the value of anisotropic parameter k=C22/22/C11/11 considerably affects the displacements. When the value of k becomes smaller than 1.0 (=isotropic), Uh increases greatly; on the other hand, if the value of k becomes greater than 1.0, Uv decreases remarkably. The directions of sedimentation, stratification and joints which bring out the anisotropic properties of the ground can, therefore, be thought to have very important effects on the displacements.
- Geology > Geological Subdiscipline > Geomechanics (0.48)
- Geology > Rock Type (0.48)
Summary: The CSM cell and the Goodman Jack are two borehole devices which can be used for determining in situ modulus. The paper presents laboratory and field experience obtained using the devices. Data reduction procedures are described. Advantages and limitations are discussed. The CSIR "Doorstopper" is a borehole device widely used for determining absolute stress. Discussion has been continuing regarding the proper data reduction procedures. The paper describes some new procedures for data analysis. Sommaire: La cellule de C.S.M. et le Verin Goodman sont deux dispositifs de me sure de compressions en paroi de forage. Ce memoire traite de tarage des resultats de laboratoire et de terrain obtenus à l'aide de ces deux dispositifs ci-haut mentionnes. Les procedes de reduction des donnees sont decrits. Leur avantages et restrictions sont aussi presentes. La cale CSIR "Doorstoper" est un dispositif de paroi de forage communement employe pour determiner la contrainte absolue. La procedure appropriee de reduction des donnees a ete largement discute dans le memoire et des nouvelles methodes d'analyse des donnees ont ete exposees. Zusammenfassung: Die CSM Zelle und der Goodman Hebel sind zwei Borlochgerate, welche fuer due Bestimmung des in-situ Modul benuetzt werden können. Mit her Anwendung von diesen Geraten wurden in diesem Berichte die erhaltenen Laboratorischen und Feld Erfahrungen beschrieben. Weiterhin wird der Data verminderungs Verlauf beschrieben. Vorteile und Einschrankungen werden erötered. Fuer die Bestimmung der unbedingten Spannung wird meistens der CSIR Tuerhalter benuetzt. Die Eröterungen wegen dem genauem Data verminderungs Verlauf sind fortlaufend. Etliche neue Verfahren fuer die Data Analyse wurden in diesem Berichte beschrieben. 1. INTRODUCTION During recent years, considerable emphasis has been placed upon the development of computational techniques (finite element, etc.) for analyzing rock mass/structure interaction. Good success has been realized. The development of the tools and techniques for providing the required input data has unfortunately not kept pace. Of the devices constructed for use by various investigators, few have been developed to the point of commercialization. The main reason for this is that although the interest has been present there has been little money available for the development and comprehensive testing of such tools/techniques. Undoubtedly this is the result of a small potential market, the relatively high associated costs, and a high risk of failure. The potential for high costs to a construction project which can be directly attributable to poor site evaluation has received little consideration. Many of the devices/techniques which have reached the marketplace, have not, for many reasons, been evaluated under a full range of operating conditions prior to their introduction. It remains for the users to develop applications and sometimes procedures for data collection and interpretation. This paper describes (1) the use of the CSM cell, for obtaining the modulus of rigidity of the rock surrounding a borehole, (2) data reduction procedures for the Goodman Jack, and (3) data reduction procedures for the CSIR "Doorstopper Gage". The first device is presently in the prototype stage. The latter two devices are commercially available and have in the past been the subject of much discussion. 2. MODULUS DETERMINATION USING THE CSM CELL 2.1 Introduction The CSM cell (7) was developed over the period 1970–72 for determining the modulus of rigidity of the rock surrounding a 38 mm diameter borehole. If the Poisson's ratio for the rock is known or can be estimated, then the modulus of elasticity can be calculated. The CSM cell system is shown diagramatically in Figure 1. Basically it consists of an inflatable membrane (the CSM cell) which is attached to a pressurization system. An adiprene membrane is used to transmit the fluid pressure to the wall of the borehole. The seal design is similar in principle to that used by Hoek and Franklin (5) in the development of their triaxial cell. It has worked effectively at pressures up to 10,000 psi. A screw type of pressure generator connected to the cell by high pressure tubing allows monitoring of the change in system volume as a function of the applied pressure. By a calibration procedure, the change in borehole volume can be separated from the total volume change. Using the borehole volume-pressure curve and equations developed from elasticity theory, one can calculate the rigidity modulus. In this section, the procedure for using the cell will be described, applications discussed, and results presented. 2.2 CSM Cell Technique Prior to testing, the stiffness (pressure/ volume relationship) of the CSM cell system (Ms) must be determined. This is done by obtaining the pressure/volume relationship (M) when the cell is inserted in a calibration cylinder of known dimension and elastic properties. Such a calibration curve is shown in Figure 2. Some advantages of the CSM cell system over similar previous devices are (1) the adiprene membranes used to apply pressure to the borehole wall are very tough and resilient.
SUMMARY: When a solid epoxy probe with embedded strain gauges is cemented to a pilot hole in rock and overcored, the strains measured in the probe are used to infer the in situ stress state of the rock. A linear elastic analysis demonstrates that the size of the overcoring diameter must be taken into account in the analysis or incorrect predictions' of in situ stress may result. The influence of the elastic properties of the probe and the rock on the analysis is also examined. RÉSUMÉ: Quand, une sonde epoxyde solide à extensomètres incorpores a ete, cimentee à untrou pilote dans le roc et surcarottee, les deformations mesurees dans la sonde sont utilisees pour inferer l'etat de contrainte in situ, du roc. L'analyse elastique lineaire montre que la grandeur du diamètre de la surcarotte doit être prise en consideration lors de l'analxse, afin d'eviter la possibilite d'obtenir des predictions incorrectes de la charge in situ. L'influence des caracteristiques elastiques de la sonde et du roc est examinee aussi. ZUSMMENFASSUNG: Wenn eine solide epoxydische Sonde mit eingebetteten Ausdehnungsmessern in ein Pilotbohrloch im Felsen geklebt und danach ueberkernt wird, so können die in der Sonde gemessenen Dehnungen zur Ableitung des in-situ-Spannungszustands des Felsen benutzt werden. Aus einer linear-elastischen Analyse ergibt sich, dass die Grösse des Durchmessers der Überkernung bei der Analyse beruecksichtigt werden muss, anders können unrichtige Vorhersagen der in-situ-Spannung erfolgen. Der Einfluss der elastischen Merkmale der Sonde und des Felsen wird auch untersucht. Introduction Inthe last ten years several "soft-inclusion" devices have been developed to measure in situ stress from underground openings in rock (Rocha and Silverio, 1969, Rocha et al, 1974, Blackwood 1976 and 1977, Worotnicki and Walton 1976, Pender 1977). All are developments of a basic technique presented by Leeman (1968). For simplicity, the steps involved in these techniques, and the analysis of recorded strains will be described in detail initially for the particular situation where the in situ stress state can be described as axisynmetric with respect to the axis of the measuring probe. The analysis is in cylindrical polar coordinates, with the z azis along the axis of the measuring probe.A large diameter hole (75–150 mm) is drilled in the direction of the z axis. The hole is drilled to a distance sufficiently far from the investigation chamber that the effect of the opening itself on the in situ stresses can be neglected. The pilot hole must be long enough not only to neglect the effects of its own ends, but also to neglect the disturbance in stress caused by the larger "overcoring" hole in step (i). A measuring device is inserted into the pilot hole. In the original technique (Leeman1968), strain gauges were glued directly to the surface of the pilot hole. This paper is concerned with the situation where strain gauges are embedded in a solid epoxy probe which is then cemented into the pilot hole (Rocha and Silverio 1969 Blackwood et al 1976, Blackwood1977). A third technique (Rocha et al 1974, Worotnicki and Walton 1976, Pender 1977) uses a hollow epoxy probe. The assembly is overcored with the original large diameter drill (radius nR). This releases the compressive normal stresses on the boundaries of the overcored assembly, thus inducing tensile strains in the measuring devices. There is also a normal tensile stress induced across the rock epoxy interface. In sane cases this has been high enough to break the bond between the solid epoxy probe and the rock - thus ruining the experiment. The hollow probe does not suffer from this disadvantage - there is a residual normal tension normal to the epoxy-rock interface - but this is small. The purpose of this paper is to present an exact linear elastic analysis of the strains induced in the solid probe by the removal of stresses normal to the boundaries of the overcored assembly - and to demonstrate that the parameter n(which represents the ratio of the diameter of the overcored rock to the diameter of the pilot hole) can have a major effect on the analysis. For the other two techniques the problem does not arise. It is clear that in the Leeman method all stresses are released from the overcored rock, whatever its size. Panek (1966) has noted that the overcoring shape need not be circular, nor concentric with the pilot hole axis. This statement can also be applied to the hollow epoxy probe, provided the overcoring boundary is never too close to the pilot hole. There is a residual normal tension near the pilot hole, but as mentioned previously, this is very small and decays rapidly away from the epoxy rock boundary (Fama and Pender (1978). It has been concluded incorrectly, that Panek's statement is also true for the solid probe (Blackwood1976, 1977).
SUMMARY: The peak shear strength of a rock discontinuity is mainly influenced by its surface geometry. Therefore scale-effect must be considered when determining the initial friction of a potential sliding plane. Basic investigations are described which quantify the influence of scale-effect. According to these, small sample sizes lead to higher peak shear strength values than can be activated in-situ and are therefore unsafe to use in stability calculations. The consequences of the results of the basic investigations for slope stabilization by means of anchors are shown in a case study. The estimation of realistic in-situ shear strength values is somewhat more expensive but results in a saving of anchor forces of about 30 % in the particular case. Further, the consequences of the choice of the safety definition on the analytical slope stability are generally explained. RESUME: Dans les problèmes de stabilite de talus, les contraintes normales ne sont normallement pas très hautes. C'est pourquoi que la resistance au pic d'une discontinuite depend de la geometrie de la surface et est influencee dans son estimation par l'effet de l'echelle. Des recherches fondamentales pour quantifier cet effet sont decrites. Il en resulte que l'on obtient avec des echantillons sur une petite echelle des resistances trop elevees qui ne donnent pas des resultats satisfaisants pour le dessin. Par l'example d'une assainissement d'un talus, l'importance de l'estimation d'une resistance au cisaillement reelle sur l'ancrage est montree. La technique d'essai est un peu coûteuse, mais elle reduit considerablement les frais de l'ancrage. En outre, les consequences de la choix de la definition de la solidite sur la stabilite calculee du talus sont montrees. ZUSAMMENFASSUNG: Die aktivierbare Spitzenreibungsfestigkeit einer Gesteinstrennflache wird bei der lösung von Böschungsproblemen aufgrund der hier wirkenden niedrigen Normalspannung in erster linie von der Oberflachengeometrie der potentiellen Gleitflache bestimmt und unterliegt daher bei ihrer Ermittlung dem Einfluβ des MaBstabes. Es werden Grundlagenuntersuchungen Beschrieben, die diesen Einfluβ quantifizieren. Kleinmaβstabliche Versuchskörper ergeben demriach Spitzenreibungsfestigkeiten, die zu groβ sind und damit auf der unsicheren Seite liegen. Am Beispiel einer Böschungssanierung wird gezeigt, welche Bedeutung die Bestimmung eines wirklichkeitsnahen Spitzenreibungswinkels auf die Dimensionierung der Ankerung ausuebt. Die etwas aufwendigere Materialkennwertermittlung fuehrt zu einer erheblichen Reduzierung der aufzubringenden Ankerkrafte. Weiterhin wird allgemein dargestellt, welche Konsequenzen sich aus der Wahl der Sicherheitsdefinition fuer die rechnerische Standsicherheit der geankerten Böschung ergeben. INTRODUCTION Geometrical and material parameters are needed as input data to determine the stability of rock slopes analytically. In the special case of a monolithic rock mass which is able to slide on pre-existing discontinuities. only the parameters of these discontinuities viz. friction and cohesion are of interest. Sliding surfaces along joints with degree of separation (K) less than 1 are not considered here, because of difficulty in estimation of K. Further the simultaneous activation of the intact material shear strength and friction on discontinuities cannot be assumed a priori. In completely separated joints (K = 1) cohesion cannot exist theoretically, except in the hypothetical case when the inclination of asperities is i > 90° -, where is the angle of friction on a flat plane. The only interesting joint parameter is thus the frictional strength. which is characterized by peak and residual shear strength. Both these values are determined in direct shear tests because only in such tests the boundary conditions are similar to those existing in-situ (LEICHNITZ, NATAU. 1978). The use of residual shear strength as input, data in a slope stability analysis is in general very conservative, because the asperities of natural discontinuities are often interlocked and therefore lead to a higher peak shear strength. The initial friction depends mainly on the geometry of the joint so that the scale influence must be considered in interpreting test results. Experiments were carried out to quantify this scale-effect and to estimate its influence on the analytical stability of a rock slope. SCALE-EFFECT The question regarding the minimum size of a discontinuity which must be tested in the laboratory to determine the in-situ peak shear strength is often raised. Scale and magnitude effect must be analysed to answer this question (MÜLLER. 1967). Because of the scale-effect the probability of the sample containing imperfections and weakenings increases with increase in sample size. A statistical distribution of the mechanically decisive imperfections is impossible in small specimens; the consequence is a great scatter of the test results. Such elements are the macroscopic asperities or "first order irregularities" (PATION, 1966), (Fig. 1). In-situ sliding occurs on such large and flat asperities. The magnitude effect is only eliminated when the sample includes these macroscopic asperities. In general this would lead to uneconomic size of samples to be tested; the selection of a rational size is thus a matter of judgement. BASIC INVESTIGATIONS Experiments An assumption in the following discussion is the existence of only low normal stresses on the sliding plane.
SUMMARY: Observed stresses in continental rock masses commonly indicate that the magnitude of the lateral stress component exceeds the vertical component. Examination of published stress data indicates that the lateral stress is not proportional to overburden depth or to vertical stress. It is suggested that more complex relationships hold which are unique to each of the continents studied. An interpretation of this phenomenon is presented which may allow the in-situ viscous modulus of continental crustal rocks to be inferred. RESUME: Les contraintes observees dans les masses rocheuses continentales indiquent gereralement que le composant de la contrainte laterale est plus grand que celui de la contrainte verticale. Un examen des donnees dejà publiees sur ces contraintes a indique que la contrainte laterale n'est pas proportionelle ni à la profondeur des terrains de couverture, ni à la contrainte verticale. L'auteur suggète qu'il y ont des rapports plus complexes qui subsistent uniquement au cas de chacune des continents etudiès, et presente une interpretation de ce phenomène qui peut permettre l'inference de la viscosite in situ des roches d'ecorce continentale. ZUSAMMENFASSUNG: Die beobachteten Krafte in kontinentalen Felsmassen deuten im allgemeinen darauf hin, daβ die later ale Kraftkomponente gröβer ist als die Komponente in vertikaler Richtung. Die Betrachtung veröffentlichter Kraftwerte zeigt, daβ die lateralen Krafte weder der Höhe der uebergelagerten Felsmassen noch den vertikalen Kraften proportional sind. Es werden komplexere Beziehungen angenommen, die fuer jeden der untersuchten Kontinente verschieden sind. Eine Deutung dieser Phanomene wird dargelegt, die Schluesse erlaubt auf den "in-situ" Viskositatsmodul kontinentaler Felsmassen der Erdkruste. 1. THE NATURE OF CONTINENTAL STRESSES 1.1 Previous interpretations Evidence from continental rock exposures led very early to the notion that there also exist, or have existed, forces acting in directions other than vertical: folds, over thrust faults and shear zones indicate considerable compressive sub-horizontal forces, while tension gashes and normal faults demonstrated the presence of tensile or shear forces large enough to cause visible, finite strain in the solid rock. "Violently contorted rocks indicative of great horizontal compression" were noted by Fisher in 1878, who clearly saw that an average value of the coefficient of linear thermal expansion of rock did not alone account for the observed contraction of the earth's crust and suggested that some other cause of rock deformation must be sought. Observations of rock behaviour in underground mining environments led to the postulation by Fenner, 1938, of the existence of an ideal plastic, homogeneous zone of rock below an ideal elastic zone, the interface of the two regimes occurring at a depth below the surface of about 450 to 550m. Van Iterson, 1951, suggested that the pre-mining stress in coal seams would be hydrostatic, that is, the lateral stress equal to the vertical gravitational stress. The possibility of hydrostatic pressures at great depths, resulting from viscous flow of rock, has long been considered as a mechanism for certain geological processes, such as the mobilization for great movements of nappes in the building of the Swiss Alps (Holmes, 1965). As stress measurement techniques were developed, a large proportion of the measured lateral in-situ virgin stress values were found to be much greater than it was possible to predict from early speculations. At first these were regarded as anomalous since they did not fit the preconceptions held about the nature of the stress field. A notable exception to this was the work of Hast, 1957, who, on the basis of 24 measurements in Scandinavia, was led to the conclusion that, on extrapolating a seemingly linear stress-depth relationship to the surface, a horizontal stress of some 7.6 MPa might be experienced at the surface where there is no overburden pressure to act as a cause. Such a proposition was at first generally unacceptable to others due to the apparent lack of a causal mechanism. Jaeger and Cook, 1976, graph a few vertical and horizontal stress readings and, while noting Hast's values, show that other measurements agree equally well with different linear stress-depth relationships, including vertical gravitational stress, hydrostatic stress, or pressure due only to interstitial pore fluids. Other, very simplistic, views of the interaction between lateral and vertical stresses and their dependence on vertical stress are still commonplace, for example Herget, 1973; and Everell et al., 1974. Geological evidence of large, lateral, regional stresses in legion. Interpretation of the phenomena of horizontal stylolites (Wagner, 1964; Plessman, 1912), pressure shadows (Strömgard, 1913), recrystallisation by pressure solution (Durney, 1972), exfoliation (Twidale, 1964; Varnes, 1970; Brunner and Scheidegger, 1973) and sheet jointing all rely on high levels of lateral compressive stress as their major premise. It is suspected (Sykes and Sbar, 1973; Nur, 1974; Raleigh, 1974) that presently active tectonic-scale forces with influence of great areal extent are at least partly responsible for the tendency for high lateral stresses in the Australian, European and North American continental rock masses.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.46)
- Geology > Structural Geology > Fault > Dip-Slip Fault > Reverse Fault > Thrust Fault (0.34)
SUMMARY: This is an integral model of multi-component rock massif deformations. The inhomogenity, stratification, anisotropy and different module of all rock types are taken into account. The principle dynamic equations in Euler's co-ordinates, in terms, of final reversible and irreversible deformations are deduced. From the given integro-differential equations system, in partial derivatives for different components of a continuous rock massif, the equations of rock massif irreversible slow motions were received. The model offers the opportunities, the irreversible slow motions in elastic-plastic rocks to be investigated. RESUME: Un modèle integral des deformations rheologiques d 'un massif de roches à pluaieurs composantes est propose. On prend en consideration l'heterogeneite, la stratification, l'anisotropie et les modules differents des roches. Les equations principales dynamiques sont exprimees en coordonnees d'Euler dans des conditions des deformations definitives reversibles et irreversibles. Du système integral et differentiel obtenu en derivees partielles pour les composantes differentes du manif de roches continu sont deduites les equations des mouvements lents irreversibles du massif. Le modèle permet d'analyser egalement les mouvements lents irreversibles des roches elastiques et plastiques. ZUSAMMENFASSUNG: Es wird ein Integralverfahren ueber die rheologischen Deformationen des Mehrkomponenten-Gesteins - massivs angeboten. Es werden die Verschiedenartigkeit, die Uberlagerungen, die Anisotropie und der unterschiedliche Modul der einzelnen Gesteinsarten beruecksichtigt. Es werden die grundlegenden dynamischen Gleichungen in Euller-Koordinaten unter der Bedingung der reversiblen und irreversiblen Enddeformationen abgeleitet. Aus dem erhaltenen System von Integral-Differentialgleichungen in Quotientableitungen fuer die einzelnen Gesteinsmassiv-Komponenten werden die Gleichungen fuer die irreversiblen langeamen Bewegungen des Gesteinsmassivs erhalten. Das Modell ermöglicht die Untersuchung auch der irreversiblen langsamen Bewegungen im elastischplastischen Gesteinsmassiv. Sous l'influence d'excavations souter - raines à differents destinations, dans le massif de terre surgissent des mouvements qui ont un caractère lent et irreversible. Ces mouve - ments subissent l'influence non seulement de la grandeur et de la forme de l'ouvrage souterrain, mais aussi les particulatites structurals du massif de roches comme l'heterogenite, la stratification, l'anisotropie etc. A l'analyse de ces deplacements on peut constituer un modèle theorique dans lequel on doit refleter non seulement les proprietes physiques et mecaniques des roches, mais aussi le caractère de reversibilite et d'irrevarsibilite des deformations comma un continuum multiple et continu. Supposons que le massif de roches se compose de k - composantes, chacune desquelles est heterogène, orthogonalement anisotropique et de modules differents et aussi avec une même orientation des directions generales de l'ortho tropie. Après un interval de temps determine les deformations dans le massif reçoivent des dimensions definitives. Le système obtenu d'equations integrale differentielles /6/ represente le système d'equations de base qui determine, le deplacement de n'importe quel element du système multiple du massif de roches. En resolvant ce système, il faut observer les conditions du contact entre les composantes diverses. En outre cela, les contraintes sur le contour du domine considere doivent satisfaire aux conditions de la surface. Le premier et le troisième membre de I'equation /6/ expriment les deformations elastiques reversibles du massif de roches, tandis que, le second et le quatrième membre- les deformations irreversibles rheologiques. Les mouvements lents et irreversibles du massif de roches se determinent de la condition suivante: les membresdt inertie dans le sys - tème d'equation /6/ doivent être egaux à zero. Si du système des equations /6/ on elemine les membres qui determinent les deformations rheologiques du massif et si l'on neglige les modules differents des roches, on obtient les equations de base pour le deplacement dans les limites des deformations elastiques. Le massif de roches est heterogène et stratifie, mais les roches differents sont orthogonale - ment anisotropiques. Si nous supposons que, dans les equations /9/ les coeficients d'elasticite sont des grandeurs constantes et le massif est homogène et non stratifie, mais orthogonalement anisotropique, le système determinant des equations concorde avec la theorie classique d'elasticite. Il est evident egalement, que en tant que cas particulièrs, on peut obtenir les equations des deplacements quand le massif de roches est pris comme transversalement isotrope et entièrement iaotrope, ou bien stratifie avec des roches transversalement isotropiques ou entiere - ment isotropiques. En outre cela, ce modele donne la posibilite d'analyser les mouvements lents et reversibles des roches elastiques - plastiques et aussi de determiner les deformations definitives dans une periode de temps fixee. On peut analyser les mouvements plats des couches differents du massif stratifie et auesi les mouvements laminaires, unimesurables. La solution genzrale du système d'equati - ons integro - differentielles/6/ est accompa - gnee de beaucoup de difficultes mathèmatiques, mais il est applicable pour quelques cas particulièrs. Sur la base de cette resolution on peut determiner la vitesse V 1(k) du mouvement et l'etat de contrainte des roches.
SUMMARY: A series of pressurization tests were conducted in a horizontal cylindrical cavity (1.2m diameter, 7.3m length) excavated at a depth of 140m, in a rocksalt mine, to determine the in situ rheological behaviour of rocksalt. Deformation of the cavity surface and within the surrounding rocksalt mass together with the imposed internal pressure were measured and recorded with the aid of a sophisticated instrumentation scheme. Evidence of creep has been detected in the long term tests and it was found to be within the linear viscoelastic region. It was also possible to employ the relative viscoelastic analysis to estimate the values of the parameters of the rheological analogues capable of modelling the in situ time-dependent behaviour of rocksalt. RÉSUMÉ: Dans une serie d'essais destines à determiner le comportement rheologique in situ du sel gemme, on a soumis à pression interne une caverne cylindrique horizontale (diamètre 1,2m; longueur 7,3m), creusee à une profondeur de 140m dans une mine de sel. On a mesure et enregistre à l'aide d'instruments très raffines la pression interne appliquee, et les deformations tant des parois du caverne qu'à l'interieur du massif de sel gemme. Dans les essais de longue duree on a constate un fluage qui s'est trouve être dans le champ viscoelastique lineaire. Il a ete possible egalement d'utiliser l'analyse viscoelastique relative pour evaluer les parametres des analogues rheologiques capables de representer par des modèles mathematiques le comportement differe in situ du sel gemme. ZUSAMMENFASSUNG: In einer Steinsalzmine ist eine Reihe von Druckversuchen in einer horizontalen zylindrischen Kaverne (l,2m Diameter, 7,3m Lange)durchgefuerhrt worden, um das in situ rheologische Verhalten von Steinsalz zu bestimmen. Die Höhlung ist zu einer Tiefe von 140m ausgegraben worden. Die Verformung der Höhlungoberflache und der herumliegenden Steinsalzmasse zusammen mit dem auferlegten inneren Druck sind gernessen, und mittels eines komplexen Instrumentationssystems berichtet worden. Die Dauerversuche haben Kriechspuren aufgededtt und zwar in dem geradlinigen viscoelastichen Gebiet. Es war auch möglich, die relative viscoelastische Analyse zu gebrauchen, um die Werte der Parameter der rheologischen Analogen, die das in situ zeitabhangige Verhalten von Steinsalz umreissen können. 1. INTRODUCTION Investigations into certain aspects of the stability of brine cavities for the storage of gas has developed into a five years research project carried Out by the Department of Mining Engineering at the University of Newcastle upon Tyne, under the sponsorship of I.C.I. Ltd. (Mond Division). From the rock engineering point of view, an underground storage cavity is basically a container, although admitedly an extremely complex one, and the rock mechanics engineer is faced with the formidable task of estimating the structural stability of such a cavity under the operational conditions of storage, as accurately as possible. A quantitative appreciation of the structural response of such underground cavities is impossible unless a knowledge of physical mechanical properties of the surrounding rock materials can be established. Results of earlier work carried out by Budavari (1968) indicated that under certain conditions of low threshold pressure and reduction of temperature, induced during gas withdrawal there is a possibility of introducing tensile resultant stresses on the cavity surface. In this case the stress distribution around such cavities can be calculated using a mathematical analysis which will take into account the extrinsic anisotropy of rocksalt when subjected simultaneously to tensile and compressive stresses (Passaris, 1978). In addition it was shown (Thompson, 1973) that at moderate compressive levels, i.e. cavities at shallow and intermediate depth, the time dependent closure of such cavities can be reasonably analysed employing linear viscoelastic constitutive expressions. The present paper, therefore, deals extensively with the viscoelastic analysis and the tests used to define the in situ rheological behaviour of rock salt using a pressurized underground experimental cavity. The experimental cavity was excavated in rocksalt, 140m below ground in the form of a horizontal cylinder, at the Meadowbank Rocksalt Mine of I.C.I. Ltd. at Winsford in Cheshire. A diameter of 1.22m was chosen as being sufficiently large to allow access for the installation of the measuring instruments and give measurable effects, but small enough to facilitate excavation and to allow the effects of variation in the geostatic stress field to be neglected. To obtain representative data three such measuring stations were incorporated over the total cavity length of 7.3m. At each station deformation measurements were made in three radial directions, vertical, 1200 clockwise and 1200 anticlockwise. The deformation profile, in the walls of the cavity was determined using multi-point borehole extensometers equipped with linear variable differential transformers (LVDT) installed in a frame at the mouth of each borehole and their armatures rigidly connected, by means of invar extension rods, to anchors gripping the rock at four predetermined points up the boreholes. In addition the diametral deformation of the cavity was determined using extensometers equipped with LVDT and installed along the same line as the radial boreholes.
- North America > United States (1.00)
- Europe > United Kingdom > England > Tyne and Wear > Newcastle (0.25)
SUMMARY: Safety analyses regarding final disposal of radioactive waste necessitate methods to predict the influence of temperatures on groundwater movements in jointed rocks. Complex fracture geometries, spacings and openings will in the normal case require that the rock mass is treated as a hydraulic continuum. In the Swedish radioactive waste repository concept, noticeable influences of temperatures on groundwater flow are indirectly on hydraulic conductivity and directly on thermally induced flow. The latter was illustrated not to lead to the formation of convective cells but merely to cause a slight upheaval of the regional flow above the repository. The effect on intrinsic permeability and viscosity is more pronounce which is demonstrated theoretically empirically as well as in a field experiment on rock permeability at different temperatures. RESUME: Les etudes liees à la securite en ce qui concerne le depôt final de dechets radio-actifs necessitent des methodes pour la prediction de l 'influence des temperatures sur les mouvements de la nappe d 'eau souterraine dans les rocs joints. Geometries de fractures compliquees, espacements et ouvertures necessiteront dans un cas normal que la masse rocheuse soit calculee comme un ensemble hydraulique. Dans la conception suedoise concernant l'emmagasinage de dechets radio-actifs, les influences notables des temperatures sur la nappe d'eau souterraine sont indirectes sur la conductivite hydraulique et directes sur le flux thermique induit. ZUSAMMENFASSUNG: Sicherheitsanalysen betreffs entgueltiger Abfallsbeseitigung von radioaktivem Abfall erfordern Metoden, die die Einwirkungen der Temperaturen auf die Grundwasserbewegungen im Spaltgebirge voraussagen. Komplizierte Rissbildungen und Hohlraume erfordern im Normalfall, dass die Gebirgsmasse als eine hydraulische zusammenhangende Einheit betrachtet wird. Im Schwedischen Begriff der entgueltigen Ablage des radioaktiven Abfalles ist die nennenswerte Beeinflussung der Temperaturen auf den Grundwasserfluss indirekt auf die hydraulische Leitfahigkeit under direkt auf den temperaturinduzierten Fluss. Da letzte wurde erlautert nicht zur bildung auf konvektiven Zellen zu fuehren, sondern nur einen kleinen Umsturtz im regionalen Fluss ueber den schliesslichen Ablagerungsplatz zustande zu bringen. Der effekt der inneren Durchlassigkeit und Viskositat ist mehr ausgesprochen, was theoretisch und empirisch sowohl als im Feld experiment ueber Gebirgsdurchlassigkeit bei verschiedenen Temperaturen demonstriert worden ist. 1 INTRODUCTION The question of influence of moderate temperature alterations on groundwater movements in jointed rock masses has not been drawn much attention in the past. Coupled thermal and flow analysis methods have been developed in geothermal research to describe water injection to and withdrawal from hot aquiferous rocks. Fairly recently, the problems of final disposal of spent radioactive reactor fuels and wastes in hard rock became apparent. Here, methods to assesss groundwater movements in jointed rock systems under the influence of heat generation are necessary to provide input data for total safety analyses. In 1977 the Swedish power utilities initiated a special task force, Project Fuel Safety (KBS), to describe in some technical detail how and where solidified high level nuclear waste or spent reactor fuel could be safely handled and stored in an underground repository in Sweden. KBS also initiated a geological and hydrological field test program for determination of parameters which are important for the long term containment safety. This paper summarizes theoretical and experimental efforts that where done in the KBS work to assess the influence of moderate temperature increases on groundwater movements in jointed, granitic rocks {l, 2}. 2 FLOW IN JOINTED ROCK MASSES The experience from excavations and tunneling in Swedish granite indicates that in many cases horizontal jointing ("sheet jointing") is more frequent than vertical {3}. These horizontal joints are frequently open but can also be filled with clay and silt. Mapping during excavations shows that the distances between the horizontal open joints increase with depth. This means that granites with dominating sheet jointing systems will give a higher value of the permeability in the horizontal directions than in the vertical. Because of the essentially planar nature of most fractures in granite rocks, a "parallell plate" concept has frequently been used to describe the flow within the fracture {4}. Classical methods of analyses of seepage flow through porous media with Darcy flow employ a continuum model. While in the case of a jointed granitic rock mass the flow system consists of discrete fractures surrounding, essentially impermeable rock blocks, the overall flow conductivity tensor was obtained by replacing the discrete elements by a continuum with equivalent conveyance properties. Althqugh it was concluded to be desirable to model discrete fractures in the near field analysis of flow due to the repository it was found that the availability of reliable data severely limited this application. The utilized parallel plate model follows the development given by Snow {4} with conveyance properties equivalent with series of parallel fractures. Values from water-loss measurements in vertical drill holes in Sweden were utilized to assess the rock mass permeability K for the flow analyses. In Figure 1 are indicated the analyses and data required to assess the groundwater flow.
- Geology > Rock Type > Igneous Rock > Granite (0.75)
- Geology > Geological Subdiscipline > Geomechanics (0.69)
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)