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SUMMARY: The Paper describes a method, for execution of oriented borings made without previous consolidation grouting of the rock mass. Interpretation of the data obtained by this method with the aid of a computer - controlled plotter, permitted the identification of potentially unstable wedges. The analysis of positions of the wedges, and the preliminary calculation of its safety factor as to sliding, were of great value in obtaining the optimum final design for excavation of the Itaparica Dam foundations. RÉSUMÉ: Ce travail presente la description d'une methode pour l'execution de sondages orientes, realises sans l'injection prealable de consolidation du massif rocheux. L'interpretation des donnes obtenues par cette methode avec l'aide d'une "Table Traceuse" (plotter) contrôlee par ordinateur, a permis l'identification de cales potenciellement stables. L'analyse des positions des cales et le calcul preliminaire de son factour de securite quant au glissement, ont ete de grande valeur pour l'obtention du projet final optimal pour l'excavation des fondations du Barrage de Itaparica. ZUSAMMENFASSUNG: Die Arbeit beschreibt eine Metode zur Ausfuehrung von orientierten Bohrungen ohne vorhergehende Verfestigung der Felsenmasse durch Injektionen. Die Beurteilung der durch diese Metode erhaltenen Resultate, mit Hilfe eines Computers mit Zeichentisch, erlaubte die Identifizierung von potentiellen unstabilen Felskeilen. Die Analyse der Position dieser Felskeile und die vorlaufige Berechnung des Sicherheitsfaktors gegen gleiten, waren von grossem Wert fur den Erhalt des optimal en Endprojekts fur die Fundierugen des ltaparica Dammes. 1. INTRODUCTION The Itaparica Dam is located in the lower-middle section of the Sao Francisco River, on the border between the states of Pernambuco and Bahia, 450 km from the city of Recife and 520 km from the city of Salvador, in the Northeast Region of Brazil (Fig. 1). The Dam will be built as an earth - rockfill embankment on the left bank joining the concrete structures, which will house the Spillway and Power House in the right bank and in the river channel the dam will also be an earth-rockfill embankment. The crest length will be 4,700 meters, of which around 720 meters will be the concrete structures with maximum length of 105 meters (Fig. 2). When completed its ten - 240 MW generators will produce a total of 2,400 MW of energy. The spillway will be comprised of nine floodgates that will make possible a discharge of 26,500 m3/second. 2. GEOLOGY OF AREA The Sao Francisco River, in the dam area, is a superimposed river which started to excavate its bed in crystalline racks after completely cutting and eroding the unconsolidated tertiary deposits. It is not also subject to area macro-structural control, being conditioned locally just by secondary structures, such as faults and fractures, in the pre-cambrian areas, and mainly by the faulting and by differential strength of the sedimentary rocks. The differential erosion is shown by the different degrees of hardness of the exposed rocks. In extreme cases, elevations of sandstone and lowered ground of the marshlands are seen cut away in soft ground of the Mesozoic stratified shale. Erosion was very intense during the Tertiary levelling cycle, a great movement of solid load occurring then in the Sao Francisco River and its tributaries, which was responsible for the vast mantles of gravel occurring in the area. Dunes fixed by sparse vegetation occur near the alluvium belts of the banks of the Sao Francisco River, and are located over more extensive areas of Tertiary deposits. There are several different lithological groups that occur in the area, and are classified as follows: A - Undefined Pre-Cambrian rocks: represented by a crystalline complex consisting basically of migmatites, gneisses, leptynites, micaschists, quartz - schists and granites. B - The Paleozoics: represented mainly by feldspathic sandstones, with or without conglomeratic beds, and with parallel - planes and cross bedded stratifications. C - The Mesozoic: represented mainly by stratified shales claystine, siltstone, sandstones and feldspothic sandstones. D - The Cenozoic: represented mainly by sandy-clayey deposits with gravel beds, dunes consisting of silty sands, and alluvium consisting of silty-clayey sands. 3. SITE GEOLOGY The axis of Itoporica Dam was chosen in such a way that the dam would be settled on granites and migmatites instead of the sandstone area situated 5 km upstream, in order to avoid percolation problems in the banks end foundations. The weathering of granite or migmatite rocks gives a soil with a high percentage of sandy fraction, whose thickness varies from 0 to 8 meters. These saprolite are generally covered by colluvial and/or alluvium layers with thicknesses varying from 0 to 2 meters and composed of clayey and/or silty sands. The existence of granite boulders is verified throughout the dam site area. They occur both superficially over the exposed rock mass, and/or interspersed among the saprolite, colluvium and/or alluvium soils. The concentration and diameters of the boulders at the surface increases from the banks to the river channel.
- Phanerozoic > Cenozoic > Tertiary (0.74)
- Phanerozoic > Paleozoic > Cambrian (0.54)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.45)
SUMMARY: In the paper the results of analysis of in situ investigations, carried out at several dam sites, are presented. Taking into account the geological structure end the genesis of flysch rocks, the essentiel features and regularities, relating to the network of fractures as well as to their geometrical and hydraulic parameters / considered as tha random variables or functions/ have been stated. The classification of discontinuities and of the structures of flysch rock masses from the point of view rock hydraulics have been proposed. On the base of research works the method of rock mass description in the form of discontinuity models has been determined. They can be introduced as a starting point for water flow simulation on numerical or analogue models. RESUME: Le rapport presente les resultats d'analyse des essais in situ effectues sur plusieurs sites des barrages. Tenent compte de la genèse et de la structure gèologique, on a dètermine les regularites essentielles concernant le reseau des surfaces de discontinuite et de leures paramèteres geometriques et hydrauliques, en les considerent comme variantes ou fonctions alatores. On a propose une classification des surfaces de discontinuite ainsi tue de structures, des maseifs du flysch carpathen pour les problèmes de hydraulique des roches. En appuyant sur les resultats d'essais on etablit les principes de la description des massifs sous forme de '"modeles des diacontinuites qui servent comme base pour simuler les ecoulaments d'eau à l'ide des modeles analogues et numeriques. ZUSAMMENFASSUNG: Im Referat wurde die Analyse der Versuchsergebnisse in situ, welche in einigen Regionen der Staudamme durchgefuehrt wurden, dargestellt. Auf Grund der Genese and des geologisohen Aufbaues wurden die grundsatzlichen Gesetzmuessigkeiten des Diskontinuitatsnetzes des Flysches und deren geometrischen und hydraulischen Parametr /als Zufallsvariablen oder Zutal1stunktion betrachtet/ dargestellt. Eine Klassitizierung der Diskontinuitat und Structut des Flysschmassives fuer das Problem der Felsfthydraulik wurde vorgeschlagen. Die Versuchsergebnisse der wissenschaftlichen Untersuchungen haben zur Bestimmung der GrUndsltze der Beschreibung der Massive in der Form der Diskontinuitatsmodelle, welche die Grundlage der Simulation des Wasserdurchflusses auf numerischen und analogen Modellen bilden, beigatragen. 1. INTRODUCTION In the bedrock of dams the necessary protective measures against harmful effects of water percolation /grout curtains, drainage/ are generally applied, in order to secure the stability of structure and to prevent the excessive water losses from the reservoir. Their construction and extent are determined in an approximate way, taking into account the well-known empirial criteria of Lugeon or Jahde etc. The optimum method of designing should be based on the qualitative characteristic of flow-rate and hydrodynamic pressure distribution, estimated by means of flow simulation on numerical or analogue net models. The starting-point for simulation research are reliable data, concerning the geological structure and hydraulic properties of rock /C.Louis, 1970 1 W.Wittke, 1972/. These data are very difficult to obtain, because of the variety and complexity of fractured media, which are strongly heterogeneous, anisotropic and discontinuous in respect to permeability and flow conditions, especially in stratified rocks of flysch type. A study of Carpathian flysch rock masses, which are the substratum of the majority of dams constructed in Poland, has been conducted in the Institute of Hydroengineering of the Polish Academy of Sciences. Its purpose W8S to investigate the hydraulic characteristics of flysch rocks and to describe them in the form of structural models applicable for simulation /W.Jawański 1973, 1977/. The following preliminary assumptions have been involved:the flow of water takes place in open fractures of a big "hydraulic weight", forming so called "basic network of discontinuities", composed of sets of fractures, with similar spatial orientation and other main paremeters; hydraulic properties of rock masses are constant and don't depend on gradient and the state of stress /approximate assumption; this subject will be studied separately/. 2. GEOLOGICAL CONDITIONS The Carpathian flysch consists of alternating sandstones and shales with intercalations of conglomerates and mudstones. The thickness of separate layers varies from some centimeters to more than ten meters. The percentage of sandstones and conglomerates changes in a great extent from 10 % do 90 % or oven more. Taking into consideration the ratio of sandstones to shales one may distinguish the sandstone, sandstone-shale and shale complexes. Moreover the numerous faults of various magnitude, frequently accompanied by crushed end disturbed zones of rocks, appear in the massif. The degree of tectonic disturbance of the Carpathian flysch is differentiated and we may separate slightly and strongly disturbed regions in it /with block or folded structure/. The near-surface part of rocks is usually weathered and loosened by decompression. The thickness of over burden strongly decomposed zone amounts on the average 1–5 m /maximum 10–15 ml. The process of flysch rock masses formation may be divided into three principal stages a stage of lithogenesis, orogenic stage /during the alpine orogeny/ and postorogenic stage /period of morphogenesis, accompanied by relaxation and weathering of rocks/.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Structural Geology > Tectonics > Compressional Tectonics > Fold and Thrust Belt (0.89)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.86)
SUMMARY: The area of study is located at the northern tip of the Arabo-Nubian Precambrian Massif, close to the big geo-suture, known as the Syrian-African Rift Valley. The Precambrian basement is built mainly of metamorphic and igneous rocks. The area underwent many tectonic deformations during Late Precambrian (plastic and ruptural deformations) as well as during the Tertiary Period (heavy fracturing). The goal of the investigation was to find a site where large underground openings could be economically constructed. Field geotechnical work applied in the investigation included reconnaissance and detailed geological mapping, surface magnetometric surveying and core drilling. It was concluded that the caverns should be located between and parallel to the main dikes and perpendicular to the dominant set of joints (ac) to insure maximum stability. RÉSUMÉ: La region etudiee se trouve à la pointe nord du massif precambrien arabo-nubien. Le socle precambrien est constitue essentiellement de roches metamorphiques et ignees. La region a subi de nombreuses deformations tectoniques à la fin du precambrien ainsi qú a la periode tertiaire. Le but de la recherche etait de trouver un site où lon puisse economiquement realiser de vastes ouvertures souterraines. Le travail geotechnique sur le terrain realise pour cette recherche a comporte l'etablissement d'une carte geologique d'ensemble et de detail, une reconnaissence magnetometrique de surface et des sondages carottes. Il a ete conclu que les cavernes devaient être implantees entre les lignes de relief principales et parallelement à celles-ci, et perpendiculairement au reseau dominant de fissuration (ac) pour assurer la stabilite. ZUSAMMENFASSUNG: Das Gebiet dieser Studie liegt am Nordende des Arabo-Nubischen Prakambrian Massiv, in der Nahe der grossen Geo-Naht bekannt als der Syrisch-Afrikanische Graben. Die Prakambrische Basis besteht hauptsachlich aus metamorphen und vulkanischen Gesteinen. Das Gebiet erlebte viele tektonische Deformationen im spaten Prakambrium (plastische und Riss- Deformationen) wie auch in der tertiaren Periode (Verwerfung). Das Ziel der Untersuchung bestand darin, eine Oertlichkeit zu finden, in der weitraumige untertage-Kavernen ökonomisch konstruiert werden kùnnen. Detaillierte geologische Kartographie, oberflachenmagnetometrische Vermessungen und Kernbohrungen wurden angewendet. Zur Erreichung der optimalen Stabilitat wurde empfohlen, die Kavernen parallel zwischen den Hauptintrusionen und normal zur Hauptkluftrichtung anzuordnen. INTRODUCTION The area under consideration is situated 4 km south of the town of Elat and has a surface of just over 1 square km. It is formed by the rugged weathered granite hills whose highest point is 137 m M.S.L. The geology is clearly exposed throughout the arid study area due to lack of vegetation, and structural features are well expressed by the morphology. Variable courses of wadis and nick points,are due to some tectonic lines (fractures shearing planes, dikes, etc.). The occurrence of "positive" (ridge-forming) and "negative" (trench-forming) dikes as a function of the rock's resistivity to weathering is common. Geological studies intended to locate appropriate underground oil storage sites in the Elat area were started in 1972 in the Israel Institute of Petroleum and Energy (L. Koifman, Project Manager) and later on, the research has been carried on under the auspices of Petroleum Services Ltd. The authors would like to express their thanks to the aforementioned organizations. 1. METHODS OF STUDY The principal investigation tools utilized in this investigation were geological mapping, magnetometric surveying and core drilling. 1.1 Geological Mapping Initial reconnaissance geological mapping of a one slare kilometer area on a scale of 1:1000 was done with the aid of air photos to delineate the principal rock contacts and tectonic features. This map provided a picture for selection of a preferred smaller area for concentrating follow up evaluation efforts including core core drilling and detailed geological mapping. Detailed geological mapping of about one-third square kilometer was carried out using Brunton compass and tape and "plotting on a 1:500 scale topogtaphic base map, having a 0.5 meter contour interval. Four sets of maps were prepared to illustrate the following: a. Geology b. Frequency and attitude of High-angle joints trending NE-SW (overlay). c. Frequency and attitude of high-angle joints trending N-S (Overlay). d. Frequency and attitude of low-angle joints (Overlay). 1.2 Magnetometric Survey Several oriented sections were made in the area, most of them perpendicular to the dikes, and some parallel. It should be noted that the results of the magnetometric readings (M.R.) were quite persistent. On granites, schists and most parts of acid or intermediate dikes - the M.R. were of low values (less than 100 gammas), whereas on the basic dikes the M.R. were usually higher than 100 gammas. Dikes under alluvial fill could be traced by M.R. 1.3 Core Drilling Nine oblique holes were core drilled in the area in order to probe the detailed subsurface anatomy and character of the granite body in the selected area. The core drilling was carried out in two stages. In 1973 3 shallow boreholes were drilled in the southeastern part of the prospected area.
- Asia > Middle East > Yemen (0.95)
- Asia > Middle East > Saudi Arabia (0.95)
- Africa > Sudan (0.95)
- (4 more...)
- Proterozoic (0.98)
- Phanerozoic > Cenozoic > Tertiary (0.68)
- Hadean (0.67)
- Archean (0.67)
- Geology > Structural Geology > Tectonics (1.00)
- Geology > Rock Type > Igneous Rock > Granite (1.00)
SUMMARY: The mechanism of rock fracture around underground openings is a problem of fundamental nature so far as the stability of the excavation is concerned, because the safety of excavation to a large extent depends on the control of such fractures. Presently the stability analysis is based on load-deformation behaviour of rock mass which for practical reason is difficult, time consuming and uneconomical. If, however, the study be made on fundamental aspects of fracture growth around openings by testing small scale rock models of typical excavations assisted by photo-elastic observations, it will be helpful in predicting at the planning stage itself the areas of high stress zones that are likely to built up at the time of underground excavations. RESUME: Le mecanisme de fracturation des roches autour des cavites souterraines est un problème fondamental en ce qui concerne la stabilite des excavations, car la securite de l'excavation depend dans une large mesure du contrôle de telles fractures. Actuellement, l'analyse de stabilite est basee sur le comportement "charge - deformation" des roches. Cependant, pour des raisons d'ordre pratique, cette analyse est difficile, coûteuse et exige beaucoup de temps. Pourtant, si l'on etudie les aspects fondamentaux du developpement des fractures autour des cavites souterraines moyennant des essais sur des modèles reduits de differents types d'excavations accompagnes d'observations photoelastiques, cette etude permettra de predire, au debut même du projet, les zones de contraintes elevees qui sont susceptibles d'apparaître lors d'excavations souterraines. C'est dans ce but que les auteurs ont essaye de resumer les resultats sous forme de recommandations pour le projet de cavites circulaires juxtaposees. ZUSAMMENFASSUNG: Der Mechanismus des Felsbruches rund um Felshohlraume ist insofern ausserst wichtig, als die Stabilitat des Hohlraums weitgehend von der Kontrolle solcher Brueche abhangt. Zur Zeit basiert die Stabilitatsanalyse auf dem Last-Verformungs-Verhalten der Felsmasse, welche in der Praxis sehr schwierig, zeitraubend und kostspielig ist. Wenn hingegen die Analyse im Hinblick auf fundamentale Aspekte des Bruchwachstums um die Hohlraume mittels kleinmassstablicher Modellversuche fuer typische Felshohlraume, unterstuetzt durch spannungsoptische Beobachtungen, durchgefuehrt wird, wird die Voraussagung der Gebiete hoher spannungskonzentration, deren Entstehung wahrend der Ausbrucharbeiten wahrscheinlich ist, schon bei der Planung erleichtert. Die Autoren haben versucht, die Ergebnisse fuer die Planung kreisförmiger Doppelröhren in der Form einer Anleitung zusammenzufassen. 1. INTRODUCTION The problems encountered in the design of underground openings are of complex nature. The complexity arises due to the interrelationship of premining stresses, material properties and the goemetry of excavation. The first two variables are governed by natural conditions and the only one on which one can exert some control is the geometry of the opening. In nature the undisturbed ground is in equilibrium and during the process of excavation the equilibrium is disturbed and redistribution of field stresses takes place. This causes stress concentration at the surface of the opening. Therefore while designing an underground structure in rock or evaluating the stability of an existing structure, one must determine,the stress/or deformation in the structure resulting from premining field - stress and the ability of the structure to withstand these stresses or deformations (Verma et. al. 1976; Ratan. and Dhar, 1977). If stress distribution around an opening significantly effects the stress distribution around other opening and vice-versa, the interacting combination is referred to as multiple opening. Keeping these observations in mind, openings are to be so oriented that the critical stresses do not exceed the rock strength. The fracture propagation around an opening is the result of the concentration of tensile stresses or compressive stresses at the boundary of the opening. The presence of such tensile stress concentrations in general are dangerous for brittle materials as they are usually weak in tension. However, it is possible that the fracture study in models may not exactly give the magnitude of stress concentration, but they help in locating the zones of concentration and the nature of forces, which are important for a designer. To withstand the stresses, developed, a designer cannot select a particular rock having greater strength, the factors he can thus consider are (i) the shape of the opening that will minimise critical stresses or strain rates and (ii) the orientation of openings which will ensure a resettled stress distribution. Since premining field stresses and rock properties are governed by natural conditions, the designer can not apply the same analytic procedures, or achieve the same preciseness in designing rock structures as is realised in the design of conventional structures. In fact it must be accepted from beginning that a different approach to the problem of designing rock structures should be developed - one in which the designer realises that only an approximate design can be made before underground access - is possible, and that this design must be modified as information from underground investigation becomes available (as a result of development or progressive mining operation).
SUMMARY: The borehole impression probe is a wireline tool that gives a permanent record of the intersections, of discontinuities with a borehole wall. The probe was used to obtain 'the discontinuity orientation data required for a study of the causes of failure of a wharf structure founded on highly jointed rock. Because of constraints imposed by the nature of the site, other discontinuity survey techniques could not be used, and the only discontinuity orientation data available for analysis was that satisfactorily obtained with the impression probe. RESUME: Le "borehole impression probe" est un instrument à cable qui permet un enregistrement continu des intersections entre discontinuities et parois de sondage. Cette sonde a ete utilisee afin d'obtenir des donnees dur l'orientation des discontinuites dans Ie cadre d'une etude sur les causes de rupture d'une structure de quai fondee sur une roche hautement fracturee. Les contraintes imposees par la nature de site n'ont pas permis d'utiliser d'autre technique de reconnaissance de discontinuite, les seules donnees d'orientation de discontinue disponibles pour l'analyse furent obtenues grace à l' "impression probe". ZUSAMMENFASSUNG: Die Bohrloch-Eindruckssonde ist ein mit einem Kabel verbundenes Werkzeug, welches eine dauerhafte Aufzeichnung der Schnittstellen der Unregelmassigkeiten mit der Bohrlochwand ermöglicht. Die Sonde wurde verwendet, um Unregelmassigkeits- Orientierungsdaten zu erhalten, welche fuer eine Studie ueber die Gruende fuer den Zusammenbruch einer Kaistruktur auf der Grundlage von stark zerklueftetem Fels erforderlich waren. Wegen der Einschrankungen, die Natur an dieser Stelle auferlegte, konnten keine andersen Unregelmassigkeits-Pruefverfahren verwendet werden, und die einzigen, zur Analyse verfuegbaren Unregelmassigkeits-Orientierungsdaten waren diejenigen, die auf zufriedenstellende Weise mit der Eindruckssonde erreicth wurden. 1. INTRODUCTION 1.1 Importance of discontinuity orientation data The attitudes and mechanical properties of discontinuities intersecting rock masses often exert a dominant influence on the behaviour of engineering structures built on or in rock. Indeed, a significant proportion of all rock mechanics work in both research and practice is concerned with the location, description and measurement of discontinuities and the assessment of their likely influence on the behaviour of rock mass structure systems. It is usually desirable that as much as possible of the location, description and measurement of discontinuities be carried out from surface outcrops or from investigation boreholes. Generally, more detailed information can be obtained from exploratory and trial underground excavations, but for many projects, the geotechnical information required for site selection may be needed before such underground excavations can be made. In other cases, such as foundations of some civil engineering structures, the high cost of underground exploration is not justified. In these situations, the engineer must rely heavily on borehole information. 1.2 The borehole impression probe In many cases, where core recovery is poor or it is not possible to correctly orient the core once it has been removed from the borehole, an attempt must be made to obtain the required discontinuity occurrence and orientation data using down-hole tools. Although a number of downhole techniques for recording discontinuity information have been developed, they are not always simple to apply or reliable in practice (Goodman, 1976; Barr" 1977). The borehole impression probe developed at Imperial College, London (Hinds, 1–974;Barr and Hocking, 1976; Harper and Hinds, 1977), is a downhole discontinuity measurement tool that has the advantages of simplicity, accuracy and low cost. The principle on which the operation of the impression probe is based has long been used in the oil industry to determine the orientation of hydraulically induced fractures at depth. Fraser and Pettitt (1962) described the use of borehole packers made from a special rubber element that has sufficient "memory" to bring an impression of the borehole wall to the surface after being pressurized for a reasonable time. A more sophisticated instrument was described by Anderson and Stahl (1967). More recently, Haimson (1978) has described the application of such packers to in-situ stress measurement by the hydraulic fracturing technique. For the geotechnical applications for which it was developed, the low pressure probe to be described herein offers several advantages over the more robust, higher pressure oil industry tools in terms of cost, ease of handling, reliability of results and re-use of the tool. The probe has been described in detail by Hinds (1974), Barr and Hocking (1976) and Harper and Hinds (1977), and only a short description will be given here. The borehole impression probe is a wire line tool in which a central supporting rod passes through an approximately 1.7m long section of pneumatically inflatable rubber packer material. Overlying the packer are two metal shells suitably curved to match the borehole wall. For each impression record, a blank strip of extremely deformable thermoplastic film is mounted over the foamlined curved plates. By means of an air line which is constructed integrally with the wire line suspension, the packer is inflated forcing the side plates against the borehole wall.
SUMMARY: A new method of a direct calculation of the strength of a concrete structure contact with a rocky foundation is being developed. This method is based on Griffith's approach to the evaluation of strength of brittle bodies with cracks. The contact fracture criterion formerly elaborated, is used for the calculation of the structure and also for determining the contact strength by the data of the field shear tests of stamps. Some results of the calculations on concrete dams erected in the USSR and the data of experimental proof of the strength criterion are given. RESUME: On decrit le methode du calcul direct de la resistance du contact de l'ouvrage avec la roche, base sur l'approche de Griffits à une estimation de la resistance des corps fragils avec des fissures. Le critère de destruction du contact compose jadis est utllise aussi bien pour le calcul de la construction que pour la definition du limite de la resistance du contact d'apres les donnees obtenus pendant les epreuves de champs au deplassement des etampes. On a cite de certains resultats du calcul des barrages en beton construits en URSS et des donnees de la verification experimentale du critère de resistance. ZUSAMMENFASSUNG: Zur direkten Berechnung von Festigkeit der Kontaktzone zwischen Betonbauwerk und Felsfundamentsohle ist eine neue Methode entwickelt worden, die auf Griffitsstandpunkt zur Berechnung von Bruchörperfestigkeit mit Rissen begruendet ist. Das frueher ausgearbeitete Kontaktbruchkriterium wird sowohl zur Berechnung des Bauwerkes als auch zur Bestimmung der Kontaktfestigkeitgrenze, durch Feldstempelschubversuchergebnisse verwendet. Hier werden einige von Berechnungsergebnissen bezueglich auf die in der UdSSR erbauten Betondamme und Versuchspruefungergebnisse des Festigkeitskriteriums vorgelegt. The calculations of the hydrotechnical concrete structure usually consist in the comparison between the ultimate stresses and design resistance of the concrete. However, this approach is not applied to such an important area as the construction contact plane with the foundation is. In this case the direct calculation of the strength is substituted by the evaluation of the structure shear stability. As far as structures on soil foundations are concerned, the exhaustion of the bearing capacity may in fact result in the displacement of the structure in respect of the foundation. Therefore, in this case the shear stability calculation corresponds to the limiting state possible. It is quite different in the case of the concrete construction on a rocky foundation. Concrete and rock are materials with similar mechanical properties, the structure and rock representing a system which is identical to a monolithic solid. This is confirmed by field shear tests on concrete stamps on the rocky foundation. In the course of these tests the formation of the cracks or their opening in the foundation at the stamp pressure face is observed at a certain value of load (Fig.1). Only after the destruction process of the rock under the stamp is completed, the latter is displaced in respect of the foundation. In this connection the calculation of the shear stability of the concrete construction on a rocky foundation is somewhat fictitious; it corresponds to such a limiting state that means the break-through of the pressure front. causing disastrous effects. However. the experience of maintenance of gravity clams shows that the initial stage of the contact fracture. i.e. the formation of the crack of rupture, is also of considerable danger. Here a rupture of the grout curtain and damage of other umpervious structures can be caused. Infringement of the normal conditions of existence of the structure forces to carry out expensive repairing work and reduces durability of the structure. To prevent this state of the structure, the authors recommend a special calculation of the local contact strength at the pressure face. In principle it does not differ much from the calculation of other structural elements. However, the essential distinction is that the stress at point A in Fig.1 according to the theory of elasticity have a singularity of r-¹/ type, where r is the distance between the point in question and that of A [3]. This eliminates the possibility of applying phenomenological theories of strength and necessitates turning to mechanics of brittle fracture. There are different approaches to elaborating the criterion of brittle fracture. In regard to such materials as concrete and rock Griffith's theory [7] or its development [8] are given preference to. Paper r[2] gives the generalization of condition (1) for an anisotropic foundation. There have been carried out a great many of field tests in the USSR. The results of the tests were used for examining criterion (1). Knowing the load on the stamp at the moment of the initial contact destruction, it is possible to compute by the programs available corresponding factors K1, KII at point A (Fig.1) and evaluate by means of formulas (3) and (1) stress s which equals to the tensile strength of contact with the rock for the given stamp.
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)
SUMMARY: An elastic solution for the distribution of stress around a circular bore in a uniform three-dimensional field is applied to predict failure in mine rock passes. The modes of failure considered are: compression of intact rock, shearing of joint planes and extensive strain fracturing. The calculated stresses or strains are expressed as proportions of the corresponding parameters at failure. The proportions are defined as strength indices in respect of the three modes of failure. Four case studies are presented. The various failures observed in the field are illustrated photographically. It is shown that the conditions prevalent in the rock passes considered could be predicted from the calculated strength indices. RESUME: Une solution elastique pour la distribution de stress autour d'une nodule circulaire dans un champ uniforme à trois dimensions, est utilisee pour la prediction d'echecs dans les puits de mines. Les genres d'echecs en question Bont les suivants: Compression de gisements vierges, laminage de plans joints et fractures extensives par suite de tension. Les calculs de stress et d'intensite sont exprimes sous forme d'une moyenne proportionelle du paramètre correspondant, au moment d'echec. Les proportions des trois possibilites d'echec sont defines sous forme d'incides d'intensite. Quatres etudes de cas sont soumises. Les echecs varies enregistres sont illustres a l'aide de photos. Il est demontre que les conditions existantes des gisements en question peuvent être predit à l'aide de calculs d'indices d'intensite. ZUSAMMENFASSUNG: Eine elastische Lösung fuer die Druckverteilung (ring..) herum eines kreisrunden Balls in einem gleichförmigen dreidimensionalen Felde, ist verwendet zur Voraussage von Bruchbedingungen in Grubengesteinstunnel. Die beruecksichtigten Brucherscheinungsformen sind: Zusammenpressen von intaktem Gestein, Abscheren von verbundenen Flachen und extensive Spannungsbrueche. Die berechneten Spannungen oder Belastungen sind ausgedrueckt als Proportionen der entsprechenden Parameter bei Bruechen. Die Proportionen sind definiert als Bruchfestigkeitsmerkmale, hinsichtlich der drei Brucherscheinunsformen. Vier Sachstudien sind unterbreitet. Die verschiedenen Brucherscheinungsformen, im Felde beobachtet, sind photographisch illustriert. Es wird gezeiet, dass die Voraussetzungen vorherrschend in den beruecksichtigten Gesteinsmassen vorausgesagt werden könnten von den berechneten Bruchfestigkeitsmerkmalen. 1. INTRODUCTION The ore and waste passes in a gold mine are usually situated in the shaft pillar area and are usually alternately directed between successive levels. It is current practice to raisebore these openings to a diameter of2,13m. Passes between successive levels could be as long as 100m, compared to the overall vertical extent of an entire rock pass system of as much as 1000m. The dip angles of individual passes vary between 0 deg and 35 deg from the vertical. They usually dip either in the same direction or at 180 deg to the dip direction of the strata. The dip angles of the strata vary typically between 0 deg and 35 deg. Rock passes are subject to considerable variations in field stress and geological conditions. In the design for the stability of the rock passes these conditions are to be considered. Detailed designs of rock passes are usually not conducted at the stage when a new mine is planned. The layouts of service excavations have largely become established by long standing practice and are consequently relatively inflexible in principle. Although' the walls of rock passes are known to fail reasonably frequently the predominant mode or modes of failure are not clearly understood. In order to determine the conditions conducive to failure and also to determine whether failure could be reliably predicted Goldfields of South Africa Ltd undertook a preliminary investigation of the problem. Steffen Robertson & Kirsten Inc assisted in the project, the findings in respect of which are reported in this paper. 2. TYPICAL GEOLOGICAL PROFILE ENCOUNTERED IN ROCK PASS SYSTEMS The No 1 and No 2 sub-vertical shafts on the Kloof Gold Mine, together with their associated rock pass systems, are situated in the footwall succession of the Ventersdorp Contact Reef. These rocks are typical of the most difficult geological conditions in which rock passes can be situated. Their lithology is described in some detail in Table I. The succession belongs to the Kimberley, Elsburg and Main-Bird Series of the Ventersdorp System and comprises in principle glassy quartzites, argillaceous quartzites with numerous partings and laminated aranaceous shales and conglomerates sometimes containing either argillaceous or aranaceous partings of varying thickness. These rocks evidently vary considerably in strength, elastic properties and structural behaviour. It has been observed with reasonable certainty that the orientation of rock passes relative to the geological structure has a definite influence in some cases on the mode of failure of the excavation walls. For example in a layout of alternately directed passes, the passes perpendicular to the bedding are often less adversely affected compared to the passes dipping in the same direction as the strata. One of the objects in this investigation was to determine on a quantitative basis the influence of the geological environment on the stability and competence of the rock pass walls..
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.78)
- Geology > Mineral > Native Element Mineral > Gold (0.56)
- Geology > Rock Type > Metamorphic Rock > Quartzite (0.49)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
SUMMARY: Bituminous coal of this region has three distinguishable mechanisms of deformation and failure:squeezing deformation along bedding planes governed by shear flow of soft layers (load perpendicular to bedding); slip displacement along inclined bedding planes governed by shear movement along blocks (load inclined to bedding); and brittle fracture governed by strain concentration and its sudden violent release (load parallel to bedding). The understanding of the behaviour of this coal through elucidation of these mechanisms is of particular importance in the evaluation of mine stability and in the selection of design paremeters. RESUME: Le charbon bitumineux de cette region possède trois mecanismes distincts de deformation et fracture:deformations par compression le long de plans de deposition gouvernees par l'ecoulement dû au cisaillement des couches peu resistantes (pression perpendiculaire au plan); deplacement par glissement le long de plans inclines gouverne par un cisaillement le long de blocs (direction de pression inclinee par rapport au plan); fracture friable gouvernee par la concentration de fatique et son relachement soudain (pression parellèle au plan). Il est particullèrement important de comprendre le comportement mecanique de ce charbon, par elucidation de ces mecanismes, pour 1'evaluation de la stabilite des mines et la selection des paramêtres de construction. ZUSAMMENFASSUNG: Bituminose Kohle in den kanadischen Rocky Mountains hat drei unterscheidbare Mechanismen fur Verformung und Zusammenbruch:Extrusionen entlang Schichtflachen, verursucht durch sherungsverformungen von weichen Lagen (Belastung senkrecht zur Schichtung); Verschiebung entlang geneigter Schlchtflachen, verursacht durch Scherbewegung entlang an Blocken (Belastung genelgt zur Schichtung); Sprodigkeitsbruch verursacht durch Belastungskonzentration und deren plotzliche, gewaltsame Entspannung (Belastung parallel zur Schichtung). Es ist von besonderer Bedeutung fur die Berechnung der Grubenstabilitat und Wahl der Bauparameter, das Verhalten dieser Kohle, durch Erklarung dieser Hechanismen, zu verstehen. 1. INTRODUCTION The mechanical properties of coal materials are influenced by regional sedimentary and tectonic processes with five basic geological-tectonic features governing structural defects in coal seams:The spacing and lateral continuity of layers in a coal seam result from variations in fabric and composition. Layers are the basic element of structural discontinuity. Petrological composition, which is determined by particular components and degree of coalification, distinguishes different layers in a seam. On the basis of strength, coal layers can be classed as hard (dull), soft (bright), and fibrous (very lustrous). Layer thicknesses vary from several millimetres to more than one metre. Soft coal tends to deform by extrusion whereas hard coal layers tend to constrain the other layers of coal. Cleats and cracks which are almost perpendicular to bedding are producted by internal forces during compaction of the coal seam and by external forces during tectonic movements. They are well developed in soft, bright coal layers but are almost absent in hard coal layers. Cleats and cracks in soft layers cause Its yielding behaviour (Protodyakonov, 1958). However, the influence of cleats and cracks on mine stability varies with the orientation of loading. This is demonstrated by cracks opening when the load is normal to bedding (loose coal) and by cracks closing when the load is parallel to bedding (compact coal). Tectonic deformation has rotated originally horizontal seams to various angles of inclination. The inclination is of paramount importance in evaluation of mine stability because the behaviour of coal varies greatly with the loading angle. Tectonic shearing along bedding planes fractures thick soft coal layers and disintegrates both thin soft and fibrous layers. As a result of this orogenic process the original strength of the coal is reduced and deformation of Individual layers by shear displacement and shear flow along these tectonically sheared planes is greatly facilitated. The differing behaviour of coals with different load orientations obviously is strongly influenced by geological structural defects. Three basic mechanisms of deformation and failure of coal are squeezing deformation, slip displacement, and brittle fracture. Coals of higher rank (semi-anthracite) and lower rank (high volatile bituminous) are harder and of higher strength than low and medium volatile bituminous coals which are the subject of this study. 2. EXPERIMENTAL PROCEDURE The samples for compressive strength testing were cut from large coal lumps from three underground mines: No.4 Mine - Mcintyre, No. II Mine - Mcintyre, and Vicary Creek Mine - Coleman Collieries. The sample cores were cut by a diamond coring bit using a specially designed drilling machine in the laboratory of the Department of Mineral Engineering, University of Alberta. The cored coal specimens were cylinders with diameters ranging from 43.7 mm to 76.2 mm and lengths approximately twice the diameter; the ends were finished plane and parallel to 0.25 mm. An additional 9 prismatic blocks were cut with a circular saw to simulate mini-pillars with a constant height of 2.5 cm and lengths from 2 to 15 cm for loading normal to the bedding.
- Geology > Structural Geology > Tectonics (1.00)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (1.00)
SUMMARY: In the Stripa mine, central Sweden, a pilot heater test has been carried out at 346 m level in a jointed granite. A central main heater with a length of 3 m, a diameter of 30 cm and a total power of 6 kW was placed at the bottom of a 10 m deep borehole. At different distances from the heater, stress and temperature changes were monitored. Measurements of movements along major fractures on the surface and changes of water inflow in boreholes were also carried out. RESUME: Dans la mine de Stripa, Suède centrale, une experience de rechauffement a ete realise au niveau de 348 m dans un granite fracture. Une unite centrale de chauffage d'une longueur de 3 m, d"un diamètre de 30 cm et d"une puissance totale de 6 kW, fut place au fond d"un sondage de 10 m de profondeur. Les variations de tensions et de temperatures furent enregistrees à differentes distances de cette unite. Des mesures de mouvements Ie long des fractures majeures en surface et des variations de l'afflux des eaux dans les trous de sonde furent egalement realisees. ZUSAMMENFASSUNG: Im Bergwerk Stripa in Mittelschweden auf dem 348 m - Niveau ist ein Ervarmungsversuch im rissreichen Granit unternommen worden. Ein 3 m langes Heizelement mit dem Durchmesser von 30 cm und Gesamtleistung von 6 kW wurde auf den Boden eines 10 m tiefen Borloch gestellt. An verschiedenen Abstanden von dem Heizelement wurden die Spannungs- und Temperaturveranderungen gemessen. Weiter- hin hat man die Bewegungen entlang den Hauptrissen auf dem Boden des Ortes und die Veranderungen im Wasserumsatz im Borloch gemessen. 1. INTRODUCTION In order to solve the problems with nuclear waste storage, the Swedish nuclear power industry organized the Nuclear Fuel Safety (KBS) during the late fall of 1976. Some of the research was performed at Stripa, an abandoned iron ore mine in the central part of Sweden. Adjacent to the abandoned ore is a large granite body in which all experiments have been carried out. A co-operative program was developed when a contract between US ERDA and SKBF (Swedish Nuclear Fuel Supply Company) was signed during the spring of 1977. The Swedish part of the program was developed by KBS and the US part is carried out by LBL (Lawrence Berkeley Laboratory). The research program is concentrated on two major tasks; a full scale heater test and a time scale heater test. In both cases cylindrical heaters simulating nuclear waste canisters, will produce a flow of heat into the granite. For a period of two years, temperature, stress and displacements will be measured in the rock. In connection with the heater tests an extensive geophysical and hydrological program will be carried out. A pilot heater test has been accomplished by the Department of Rock Mechanics, University of Luleå for the KBS project. The purpose of the test was to determine stress and temperature changes around a cylindrical heater in the rock. Measurements of displacements along major fractures on the floor of the test site and of changes of water inflow into boreholes close to the main heater were also performed. Furthermore, comparison between the in situ modulus of unheated and heated rock were carried out. The pilot heater test was scheduled for a test period of five months, where two months were planned for heating and three for cooling. 2. TECHNICAL DESCRIPTION In order to facilitate the boundary conditions in the numerical calculations, it was decided to orientate the heater test so that all measurements were performed in the in situ σ1-σ2 plane, i.e. all boreholes should be drilled parallel to the least principal stress, σ3. Furthermore, it was decided to locate all measurement points in the midplane of the heater. The in situ stresses were determined by Department of Rock Mechanics, University of Luleå. The measurements were based upon the Leeman three dimensional overcoring principle. A 20 m long borehole close to the heater test site was used to determine the stress tensor at 19 data points along the hole. The mean values of the principal stresses are plotted in Figure 1. A detailed description of the results is given in [2]. In order to determine the site isotropy of the thermal and mechanical properties, measurements of stress and temperature changes have been made in three separate radial directions, from the axis of the main heater. To facilitate further discussions in this paper the different c:rections are hereafter referred to as A, B and C respectively. A schematic picture of the hole configuration for the heater test is shown in Figure 2. Temperature and stress changes were monitored by using thermistors and vibrating wire gauges at a minimum distance of.85 m and a maximum distance of 2.95 m from a main heater, surrounded by three peripheral heaters.
- Geology > Rock Type > Igneous Rock > Granite (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)