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THE COMMITTEE The U.S. national group responsible for participation in activities of the International Society for Rock Mechanics is the U.S. National Committee for Rock Mechanics (USNC/RM). The Committee was formed within the National Research Council, the operating arm of the National Academy of Sciences and the National Academy of Engineering, in 1967 for three major purposes:To provide coordination and promote cooperation among the technical and professional societies and organizations involved in rock mechanics. To effect appropriate participation in all activities of the International Society for Rock Mechanics (ISRM) through the National Academy of Sciences - National Academy of Engineering - National Research Council (NAS-NAE-NRC), which adheres to the ISRM on behalf of United States scientists, engineers, and technologists interested in rock mechanics. The Committee is composed of eighteen members, including eight members-at-large and ten who are representatives of the following professional societies and organizations: Association of Engineering Geologists American Geophysical Union American Society of Civil Engineers American Society of Mechanical Engineers American Society for Testing and Materials Geological Society of America, Inc Society of Exploration Geophysicists Society of Mining Engineers Society of Petroleum Engineers Transportation Research Board National Research Council Boards with liaison members on the USNC/RM are: Building Research Advisory Board Transportation Research Board An approximate balance of representation from government, industry, and academic/research institutions or organizations is maintained among the members-at-large. The Committee chairmanship changes annually. The present chairman is Dr. Don C. Banks of the Waterways Experiment Station of the U.S. Army Corps of Engineers. The other chairmen since 1974 were:Dr. Charles Fairhurst, University of Minnesota, July 1, 1974-June 30, 1975 Mr. George B. Wallace, Bovay Engineers, July 1, 1975-June 30, 1977 Mr. Thomas C. Atchison, University of Minnesota, July 1, 1977-June 30, 1978 Mr. Sidney J. Green, Terra Tek, Incorporated, July 1, 1978-June 30, 1979 ROCK MECHANICS SYMPOSIA One of the Committee's major activities each year is to arrange for a U.S. symposium on rock mechanics. The Committee selects a university to act as host and works with that university in planning and organizing the symposium. These annual symposia are the major technical meetings devoted totally to rock mechanics in the United States at which researchers, educators, and practitioners in the field of rock mechanics can meet to discuss mutual problems and newly acquired knowledge. The symposia provide a forum for exchange of information by approximately 300 to 400 participants, representing both national and international viewpoints. The U.S. symposium was not held in 1974 because of the participation of potential hosts in activities associated with the 3rd Congress of the International Society for Rock Mechanics conducted in Denver, Colorado that year.. During the remainder of the reporting period, symposia were conducted as described below. To disseminate the information presented at the symposia, the proceedings are published and distributed to participants and other interested persons and organizations. For the reader's convenience, information on the availability of proceedings is furnished with the description of the symposia.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.56)
- Government > Regional Government > North America Government > United States Government (1.00)
- Energy > Oil & Gas > Upstream (1.00)
1. INTRODUCTION For the past few years the C.E.R.N. (European Center for Nuclear Research) at Geneva is operating its SPS (Super Proton Synchroton). This facility consists of an underground ring in form of a 5.6 m diameter tunnel of approximately 8 km in length where protons (positive loaded particles, which jointly with the neutrons build up the nucleus of any atom) are accelerated almost to the velocity of light by means of electric fields and steered around the tunnel by means of magnetic ones. The protons are introduced into the mentioned ring, that lays 20 to 60 m below ground surface, through an inclined edit. After some 100'000 revolutions they are diverted from the ring and brought to two experimental areas through two other inclined tunnels. The overall situation of the SPS/across the Swiss french border may be seen on figure 1. Recently CERN decided to develop this facility in order to accelerate in the same ring at the same time as the protons also antiprotons (which have the same mass as the protons and are electrically negative loaded) but, of course,in the reverse sense. With this arrangement the possibility arises of bringing protons and antiprotons to collide together at very high velocity, which also means at a very high level of energy. To achieve this experiments a 1'000 t heavy machinery is needed, which has to be placed across the ring but has, also to be removed from it from time to time. This makes necessary, among other works, the construction of a 30 m deep, 40 by 20 m wide shaft across the tunnel as may be seen in figure 2. The structure has to be as stable as possible in spite of the displacements of a mass of l' 000 tons and in spite of the swelling properties of the rock. The problem is once more complicated by the necessity of reducing as much as possible the shut-down time of the SPS for construction purposes and because the activity of the of the fact that during same some radioactivity appears. The workers must be protected from it by at least 5 m of rock. THE GEOLOGICAL SITUATION A wide strip of Swiss territory reaching from Geneva to Austria is build up by terciary aged marine and lacustrine deposits, the so called "Molasse" formations. They consist mainly of sandstones and marls with all the possible intermediary gradations. It is worthwhile to mention that as a general rule the swelling potential of that rock strata increases with depth and that the swelling pressures may reach the value of the rock overburden. The way the swelling develops in time is very difficult to predict since it depends on the possibility of the water to penetrate each element of the rock mass. On the contrary, the maximum possible volume increase of the rock is easy to measure on samples and the maximum deformations and pressures in the works may be computed with some accuracy.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.57)
- Geology > Sedimentary Geology > Depositional Environment > Continental Environment > Lacustrine Environment (0.55)
- Geology > Geological Subdiscipline > Geomechanics (0.51)
SUMMARY: This group report from Sweden tries to describe the general conditions and background for rock mechanics activities during the last five years. The reporters have found that the main interest has been directed towards the following areas: a) pre investigations - methods, scope and prognosis value b) rock mass permeability and hydrogeology c) rock excavation d) rock support and reinforcement e) calculation and measurement of rock mass deformation f) influence of temperature on rock masses. In every area the trends and the most important works have been shortly described and references are given. RESUME: Le present rapport de groupe etabli en Suède tente de decrire les circonstances generales et la toile de fond qui ont conditionne les activites poursuivies dans le domaine de la mecanique des roches au cours des cinq dernières annees. Les auteurs ont constate que l'interêt principal s'etait porte sur les secteurs suivants: a) etudes preparatoires - methodes, etendue et valeur des previsions b) permeabilite de la masse rocheuse et hydrogeologie c) creusement de la roche d) soutènement de la roche et renforcement e) calculs et mesures de la deformation de la masse rocheuse f) influence de la temperature sur les masses rocheuses. Dans chaque secteur, les tendances relevees et les travaux les plus importants font l'objet de brèves descriptions completees par des references. ZUSAMMENFASSUNG: Der vorliegende Gruppenbericht aus Schweden stellt den Versuch dar, die generellen Bedingungen und Beweggruende fuer die gebirgsmechanischen Tatigkeiten der letzten fuenf Jahre zu beschreiben. Die Berichterstatter gelangten zu dem Ergebnis, dass das Hauptinteresse auf folgende Teilgebiete gerichtet war: a) Voruntersuchungen - Methodik, Umfang und Prognosewert b) Gebirgsdurchlassigkeit und Hydrogeologie c) Vortriebsmethoden d) Gebirgssicherung, -ausbau, -verfestigung e) Einfluss höherer Temperaturen auf das Gebirge. Fuer jedes Teilgebiet wurden der Entwicklungstrend und die wichtigsten Arbeiten kurz beschrieben und Referenzen gegeben. 1. GENERAL CONDITIONS FOR SWEDISH ROCK ENGINEERING The great expansion in Swedish construction - including rock construction - took place during the fifties and sixties. During this period our society exploited the ever-growing knowledge about rock blasting and excavating in building waterpower stations and tunnels, subways, underground sewage treatment plants, utility tunnels, fortifications in rock etc. Although the total construction activities has been considerably reduced during the seventies, the underground construction has been slightly increasing as a consequence of a general and growing understanding of the possibilities and advantages offered by use of underground space. However, during the same period some disadvantages connected with this technique have also been recognized, for instance lowering of the ground water table causing subsidence and deterioration of wooden pile foundations and blast vibration damage. It has also been found that the administrative rules of the society for regulating underground work do not meet such an intense activity satisfactorily in congested urban areas [2:2]. The trend of the development in mining as well as in underground construction is directed towards greater depth, larger spans and more concentrated, mechanized and consequently less manned working places. All these factors emphasize the need for a full control of the rock mechanic situation as regards excavation, stability and personal safety. Especially in the last respect there is a rapidly growing demand for still better health and safety conditions, which has been supported by society. Sweden is one of the most oil-dependent countries in the world, which has led to our building big oil storage reserves underground. The oil crisis in 1973 showed us clearly how sensitive we are in this respect and has created a policy to try to steer away from this dependency. On the other hand, there is also a policy not to be bound to a too strong dependence on nuclear energy. Therefore, energy conservation, alternative energy sources (solar energy) and more rational energy use is our road for the future. Here rock mechanics will probably play an important role, for instance for nuclear reactors underground, nuclear waste storage, storage and transportation of heated gases or liquids etc. Some of these projects have already strained our capacity up to and above our present rock mechanics knowledge. This situation has been a challenge to the rock engineering science and has, in recent years, motivated large economical and personal resources for R&D in these fields. 2. PRE-INVESTIGATIONS - METHODS, SCOPE AND PROGNOSIS VALUE It is, the world over, a well-known fact that the conditions which the contractor meets in the tunnels or openings very often differ considerably from those prognosticated from engineering geology pre-investigations. This is an unsatisfactory situation, which causes much trouble during construction and often leads to filing claims for extra payment. In Sweden such claims are usually settled by negotiation or arbitration, rarely by litigation, but even so there has, especially among the contractors, been a general wish to obtain better engineering geology prognoses as an important part of tender documents for underground work[2:l].
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Geological Subdiscipline > Environmental Geology > Hydrogeology (0.86)
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: Rock mass deformability can be expressed with empirical correlations or analytical component models. The paper discusses currently used empirical correlations and analytical models and points out their limitations. A new statistically based analytical model is proposed and the relations between results of the model and current empirical correlations are discussed. The new approach improves understanding of rock mass behavior and appreciation of variance of observations. SOMMAIRE: La deformabilite des massifs rocheux peut être exprimee par des correlations empiriques et modèles analytiques. On presente et discute, dans cet article, les correlations empiriques et les modèles analytiques disponibles à l'heure actuelle. On propose ensuite un modèle analytique nouveau base sur des statistiques. On explore, enfin, les liens entre le nouveau modèle et les correlations empiriques. Le nouveau modèle permet de mieux comprendre le mecanism de la deformation des massifs rocheux et d'expliquer la variance des observations. ZUSAMMENFASSUNG: Die Gebirgsverformbarkeit kann mit empirischen Beziehungen oder analytischen Komponenten-Modellen ausgedrueckt werden. Gegenwartig im Gebrauch stehende empirische Beziehungen und Komponenten- Modelle werden besprochen und ihre Schwachen aufgezeigt. Der Artikel beschreibt dann ein neues analytisches Modell, das auf statistischen Prinzipien beruht. Ausserdem werden die Resultate, die mit dem Neuen Modell erzielt werden, mit den gegenwartig in Gebrauch stehenden empirischen Beziehungen und die Varianz von Beobachtungen zu erklaren. 1. INTRODUCTION Rock mass deformabiltiy affects the performance of essentially all structures in and on rock, from underground openings and excavations to foundations. Thus, the prediction of deformabiltiy is an important part of rock engineering. The most direct way of estimating deformability is through field testing. However, for meaningful results, field tests must subject large volumes of rock to significant stress. Therefore, the tests are expensive, time consuming, and must be limited in number. To supplement direct testing and to provide estimates of deformability when field tests are impractical, other procedures have been introduced. Broadly, these derive from empirical correlations, on the one hand, or analytical decompositions, on the other. Many such procedures have been introduced. Empirical correlations attempt to statistically relate deformability to index properties, such as RQD, or to descriptive rock mass classifications. Analytical decompositions attempt to predict deformability by summing deformations over elements of the rock mass, such as intact blocks and joints. Both approaches suffer limitations. Correlations are limited by the character of the case studies from which the baseline data come. Decompositions are limited by an inability to measure and specify parameters of the models. Improvement of these techniques is needed. To improve predictions of deformability either more and better data are required, better information is required on joint stiffness and geometries, or a tie-in is required between correlations and decompositions. A tie-in between correlations and decompositions would allow information of each type to, in part, compensate inadequacies in the other, and would allow extrapolations of correlations through decompositions. The present work indicates a connection between correlations and decompostions, which becomes increasingly apparent as the strict geometric assumptions underlying decompositions are relaxed. 2. PRESENT TECHNIQUES FOR PREDICTING DEFORMABILITY 2.l Empirical Correlations Possibly the best known correlation of deformability to indices or descriptions is that of Deere (1967), using RQD. However, others have been proposed, ranging from the refined descriptions of the German-Austrian school (Muller, 1963; Terzaghi, 1946; Stini, 1950), to intricate quantitative descriptions of Barton (1977) and Bieniawski (1975). Indices or descriptions are correlated:to deformability by correction factors on material properties that are easily determined (e.g., intact modulus), directly to a rock mass deformability, to design features (e.g., structural dimensions). Obviously, correlations are based on field studies, and are limited by the geologic richness of the calibrating cases. 2.1.1 RQD - Modulus Ratio Relations Deere's work (1967) in conjuction with co-workers was originally based on field studies at Dworshak Dam(1964). Field plate loading tests were compared with intact modulus and RQD to arrive at the empirical correlation of Figure 1. Further data were added by Coon and Merritt (1970) from other sites. All of the data, however, were from good quality rock and the lower portion of the curve is therefore poorly defined. Although Coon and Merrit noted the inadequacy of their data base, little additional data has been publicly presented. A problem with these correlations is that they are based upon jacking tests of limited load and zone of influence. Further, some RQD's are obtained indirectly by correlation with seismic velocity ratios. Although RQD is often assumed to equal the velocity ratio, this is in fact only an approximation. Finally, only a limited number of tests and sites form the basis for the correlations. 2.1.2 Direct Correlations between Descriptors and Rock Mass Deformability. Quantitative geologic descriptors like fracture spacing and qualitative descriptors of structural features and weathering have been related directly to the deformability observed under one or several structures. Boughton(1968), for example, produced a correlation at dam sites.
- North America > United States (1.00)
- Europe (0.68)
SUMMARY: Thirteen carefully scaled physical models (scale 1: 300) were used to study the two-dimensional deformation resulting from excavation of very large span openings in near-surface rock masses. The openings were excavated in stages up to final simulated spans of 50 metres. In some cases more than one opening was excavated in parallel. The models consisted of at least 20,000 discrete blocks. Joint orientations and stress levels were varied, and some models were dynamically loaded to simulate strong earthquakes(peak horizontal acceleration 0.2 - 0.7 g). RESUME: A l'aide de treize modèles soigneusement mis à l'echelle 1: 300, le present article etudie les deformations bidimensionnelles suite à l'excavation d'ouvertures à très grandes travees situees à faible profondeur dans un massif rocheux. Les ouvertures furent amenagees par etapes jusqu'à simulation de travees finales de 50 mètres. Pour certains essais, plusieurs ouvertures parallèles furent pratiquees. Les modèles, discretises au moyen d'un minimum de 20,000 blocs et avec diverses orientations des joints, furent soumis à des niveaux de contrainte variables. Afin de simuler de violents tremblements de terre, quelques modèles furent soumis à des charges dynamiques (acceleration horizontale maximale de 0.2 à 0.7 g). ZUSAMMENFASSUNG: Dreizehn sorgfaltig skalierte fysische Modellen (Geometrischer Masstab 1: 300) wurden benutzt um die zweidimensionalen Formanderungen zu studieren, die durch den Ausschub von sehr weitgespannten Hohlraumen inoberflachennahen Felsmassen entstehen. Die Hohlraume wurden stufenweise erweitert, bis zur vollen simulierten Spannweite von 50 Meter. In einigen Fallen wurden mehrere Hohlraume in parallell abgeraumt. Die Modellen bestanden aus mehr als 20,000 Einzel- Blocke. Die Orientierung der Kluftebenen und die Spannungshöhen wurde variert. Einige Modellen wurden dynamisch belastet um starke Erdbebungen zu simulieren. (Grösste horizontale Beschleunigungen waren dabei 0.2 - 0.7 g). 1. INTRODUCTION 1.1 Typical deformation magnitudes The engineering performance of large rock caverns has traditionally been learned from mining and hydro power projects, where the depth below surface is most often many times greater than the 15–35 metres span of the openings. Deformations measured in the walls and roofs of hydro power caverns generally range from about 10–40 mm, though there is a documented case where a wall moved in 126 mm (Eristov and Khechinov, 1972), and another where the arch moved down 147 mm (Imrie and Jory, 1968). 1.2 Unknown influence of free-surface The accelerating Interest in the use of near-surface underground space for purposes as diverse as food storage and nuclear power generation, forces designers to recognize the potential influence of the free surface. It is a matter of some interest whether large excavations close to the surface will SUffer similar or very different deformations when compared with their deep-seated relations. Since elastic continuum models of rock mass behaviour are increasingly suspect as the jointed near-surface is approached, it is generally necessary to consider jointing, Whether this be simulated in numerical or in Physical modelling. 1.3 Comparison of physical and numerical models The objective of these model studies is to provide deformation data to compare with monitored data from future engineering projects (i.e. underground nuclear power stations) and for comparison with some sophisticated numerical modelling that is in progress. Both numerical and physical models can be invaluable in correctly interpreting the results of displacement monitoring of important large span near-surface openings. Physical models have a double role in that they provide a check for numerical model results. The number of blocks that can be physically modelled is closer to that in practice, generally perhaps one to two orders of magnitude larger than the number that can be handled in presently existing jointed finite element programmes. 2 MODEL REQUIREMENTS The principle requirement for a model of a near surface opening is that it should be gravity loaded, besides any additional horizontal loading. It should also be large enough to simulate several hundred metres of rock mass so that boundary effects are minimized. Consequently a material of high density and low strength needs to be used. In this study a model-prototype geometric scale factor of 1: 300 was adopted, and this made it possible to simulate horizontal dimensions of approximately 350 metres and a depth of approximately 250 metres in a model measuring 120 × 80 cm. This model was "two-dimensional", having a wall thickness of 2.5 cm. A photograph of one of the models is shown in Figure 1. A two dimensional model is equivalent to the unfavourable situation in which a cavern is excavated with its long axis parallel to the strike of the predominant jointing. It is well known that such a condition leads to large deformations. (Cording, Hendron and Deere, 1972). Measured deformations should be interpreted in the light of this limitation. 2.1 Model material The model material consisted of an oven cured mixture of red lead-sand-ballotini-plaster- water. The physical properties of a range of these weak brittle materials have been described in detail by Barton (1970).
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.89)
- Energy > Power Industry > Utilities > Nuclear (0.74)
- Energy > Renewable > Hydroelectric (0.69)
SUMMARY: At depths of greater than 2000m to which the gold mines within the group are mining it is necessary to duplicate the Bhatt systems. Associated with these are large excavations that need to be excavated and supported in a high stress environment. This paper describes those methods used in the group to design, excavate and support large excavations with specific reference to hoist chambers excavated at depth. An indication is further given of some of the cost aspects and expected future developments. ZUSAMMENFASSUNG: In Tiefen grösser als 2000 m, in denen die Goldfields Gruppe arbeitet, ist es not notwendig das Schachtsysten zu duplizieren. In diesen Tiefen sind daher grosse Kavernen erforderlich, die in diesem hohen Spannungebereich ausgehoben und unterstuetzt werden mussen. Dieser Bericht beschreibt die Methoden, die innerhalb Goldfields fuer die Berechnung, den Aushub und die Unterstuetzung mit besonderem Bezug auf Aufzugs-Kavernen, angewandt werden. Des weiteren sind Angaben ueber Kosten und ueber zukuenrtige Entwicklungen gegeben. RESUME: A des profondeurs superieures à 2000m, domaine òu opere le groupe, il est necessaire de renforcer le système de soutien. Associèe avec cecis sont les grandes excavations qui ont besoin d'etre creusees et renforceel contre les tres fortes pressions exercees par l' exterieur. Cet article decrit les methodes utilisees dans le coupe pour concevoir, creuser et renforcer les grandes chambres souterraines, ainsi que les methodes specefiques d 'extraction en Profondeur. Une indication est ensuite donnee sur le cout financier et les futurs developpements esperes. 1. INTRODUCTION The gold mines in the Gold Fields Group on the Far West Rand are mining to depths of more than 2000m. Beyond this depth hoisting in one lift becomes impracticable and in order to mine deeper, sub-vertical shafts are essential. A sub-vertical shaft involves the duplication of a Bhatt system which includes chambers to house hoists, pumps and refrigeration equipment. The life of such a shaft system can be 40 years, during which time the equipment must remain operational. As mining operations have become progressively deeper over the years the influence of larger field stresses in the mining environment have been accentuated more and more. Methods which have become standard over the years were applied and have continued to be used to greater depths. The point was reached where the rock, having a finite strength, failed and proved the then current design principles and support methods outdated. This has highlighted the need for research to investigate the influence of stress on excavations at depth and the design of support methods which could be applied successfully in the new environment. During recent years research which is an on-going process has given a better understanding to these problems. This paper will attempt to show how some of these results are applied underground. By examples of recently cut hoist chambers it will be shown how rock mechanics principles have been applied in the group to design and support chambers and how this will become more essential in the future. 2. NECESSITY FOR LARGE EXCAVATIONS AT DEPTH The gold-bearing reef which is mined in mines along the Far West Rand is dipping on average between 20° and 35° and may extend for several kilometres on dip. As mines were established they mined the reef from the sub-outcrop down wards. The shafts were shallow and when it became necessary to exploit the reef to deeper levels, sub-vertical shafts were sunk. To protect these shafts, shaft pillars were left intact on the reef plane. At these depths the stresses were of little concern, firstly due to the relatively shallow depth and secondly the competent nature of the quartzitic rock, of the Witwatersrand System. An indication of the competency of these quatzites is given in Table I together with other physical rock property values for rocks in which excavations are made. Its main function was to prevent slabs of loose rock falling on equipment and to provide a smooth finish to an excavation. In the chambers situated at shallow depths no failure of the above support methods has been experienced. In chambers and drives situated at intermediate depths however, failure has occurred. In one instance a major re-support programme had to be undertaken in hoist chambers of a sub-vertical shaft in one of the mines within the group. In this case the shaft pillar had been designed before the advent of suitable computer methods and was of inadequate dimensions. Secondly the chambers were supported with a concrete lining which cannot withstand large deformations. This inadequacy of concrete as a method of support is clearly illustrated by Ortlepp (1974). The damage that excavations can suffer due to large field stresses in a shaft pillar is also shown by Isaac & Simms (1974). The gold mines in the group are expected to mine continually deeper and more extensively than in the past.
- Africa > South Africa (0.65)
- North America > United States > North Dakota > Bowman County (0.61)
- Geology > Mineral > Native Element Mineral > Gold (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
SUMMARY: On the basis of a few simple rock mechanics tests a tentative system is developed which enables one to evaluate the economic utilization range of a tunnel boring machine (TBM). The following rock indices are considered as necessary for this purpose: point-load strength index, rebound hardness, abrasion hardness and content of minerals with equal or higher hardness then quartz. These four parameters allow one to determine a new boreability index bq, as defined in this paper, which is important for the fundamental decision of whether or not a TBM can be employed. It may even allow one to estimate the penetration rate, respectively the economic range of TBM utilization. The test methods are briefly described and discussed, and test results are given. RESUME: On à tente, sur la base de quelques essais simples de mecanique des roches, de developper un système de pronostic d'utilisation d'un tunnelier (TBM). A cet effet, on considère que les paramètres suivants sont necessaires: indice de resistance ponctuelle, durete au rebond, resistance à l'abrasion et teneur en mineraux de même ou plus grande durete que le quartz. Sur la base de ces quatre paramètres on peut determiner un nouvel indice de forabilite bq, qui est important pour la decision fondamentale d'utilisation d'un TBM et qui permet eventuellement même d'estimer la vitesse de penetration et le domaine pratique d'utilisation du TBM. Les methodes d'essai sont brièvement decrites et discutees, et des resultats presentes. ZUSAMMENFASSUNG: Es ist versucht worden, aufgrund einiger weniger einfacher geotechnischer Versuche ein Klassifizierungssystem zu entwickeln, das erlaubt, den wirtschaftlichen Anwendungsbereich von Tunnelfrasmaschinen (TBM) zu bestimmen. Folgende Versuche werden dafuer als notwendig erachtet: Zugfestigkeit bei punktförmiger Belastung, Prellharte, Abrasionsharte und Gehalt an Mineralien mit gleicher oder grösserer Harte als Quarz. Diese vier Parameter erlauben die Ermittlung eines hier neu eingefuehrten Bohrbarkeitsindex bq, welcher wichtig fuer den grundsatzlichen Entscheid ist, ob eine TBM eingesetzt werden kann. Der index erlaubt möglicherweise auch die Abschatzung der zu erwartenden Vortriebsgeschwindigkeit, bzw. den wirtschaftlich guenstigsten Anwendungsbereich. 1. INTRODUCTION The decision of whether a tunnel boring machine (TBM) can be used or not for the realization of a tunnel project depends principally on the cutter costs and on the rate of expected heading advance (ROBBINS. 1970; TARKOY, 1974). The latter is on the one hand a function of pure technical factors, such as type of machine selected, handling and maintenance of TBM, but on the other hand it is also a function of the geological conditions such as rock type, fracturing, stability of excavation and water inflow. The technical factors can be well controlled by adequate organization, so that generally the geological conditions constitute the critical factor. Of the different geological parameters of importance for tunnel boring, only one can be determined approximately by physical testing methods, namely the bore ability of the rock. As all the tests are made on samples, the bore ability is a characteristic of rock which is valid only for the sample and not for the rock mass. Since the penetration rate (bored length per machine hour) and the cutter costs depend on the bore ability, numerous methods have been developed to quantify the term bore ability which is a function of the rock's strength. hardness and abrasive properties but also of its mineralogical composition and its texture. Unfortunately, there is no method which would permit one to establish the bore ability of rock in a quick, cheap and simple manner. Many of the proposed methods require sophisticated testing equipment or difficult techniques which make it impossible to test a large number of samples under the simple conditions. which often occur in non-industrialized countries. Confronted with the above problem, during the geotechnical investigation for the 26 km long power tunnel of the Pueblo Viejo Project, Guatemalas biggest hydro-electric scheme now under construction, the authors attempted to develop a system which qualifies the boreability of rock in a similar manner as the methods proposed by TARKOY (1974] and RUTSCHMANN (1974], namely on the basis of 4 parameters which can be determined easily be means of well introduced instruments or methods;The tensile strength, determined with the point-load strength apparatus The rebound hardness, with the so called Schmidt rebound hammer The abrasion hardness, with the Los Angeles rattler test The abrasiveness (content of minerals with equal or higher hardness than quartz), by chemical, optical or X-ray methods. These 4 parameters allow to determine a bore ability index bq, which classifies the rock with reference to its aptitude to be bored by a full-face tunneling machine and to estimate the penetration rate of a TBM in a given rock type. 2. DESCRIPTION OF PERFORMED TESTS 2.1 Point-load strength index This test consists of compressing a cylindrical (core sample) or any shaped specimen (irregular lumps) between two peaks with standard dimensions.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Mineral > Silicate > Tectosilicate > Quartz (0.66)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.48)
- Machinery > Industrial Machinery (1.00)
- Energy > Oil & Gas > Upstream (1.00)
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: In Yanahara mine continuous field measurements of deformation, inclination, variation in stress and absolute value of stress have been made at many points in rock with the advance of pillar-robbing, aiming at a high extraction percentage without causing surface damages. The measurements have given evidence that though the ore body and the ground around it have deformed largely and irregularly, no serious fracture of rock has secured to this day when 67% of ore has been already mined. It is expected that a little further pillar-robbing may be possible without causing surface damages by filling goaves completely and by careful monitoring of deformation of rocks. RÉSUMÉ: Dans la mine de Yanahara on executait les mesurages continuels de la deformation, de l'inclination, de la variation de la contrainte et des valeurs absolues de la contrainte sur nombreux points dans la roche avec l'avancement de l'extraction des piliers afin d'elever le pourcentage d'extraction de minerai sans causer du dommage à la surface du sol. Les resultats de ces mesurages nous ont permis de constater que, quoique le corps mineral aussi bien que le terrain qui l'entoure aient ete excessivement et irregulièrement deformes, aucune fracture serieuse n'est pas observuee jusqu' à aujourd'hui où il a ete extrait 67 pourcent de minerai. Si on remblaie complètement l'arrière-taille et que l'on exerce attentivement Ia surveillance sur la deformation de la roche, on pourra sans doute avancer un peu plus d'extraction des piliers sans causer du dommage à la surface du sol. ZUSAMMENFASSUNG: In der Absicht, ohne Schaden von Erdoberflueche in Yanahara Bergwerk höhe Anteilszahl des Gewinns zu erreichen, werden die Kontinuierliche Feldvennessungen von Deformation, Neigung und Veranderung und absolutem Wert der Beanspruchung an vielen Punkten von Gebirge druchgefuehrt. Daraus ergibt sich, dass kein auffallender Bruch des Gebirges bis heute nach dem Abbau von 67% des Erzes aufgetreten hat, obwohl sich der Erzkörper und Gebirge in der Nahe davon stark und unregelmassig deformieren. Es ist erwartet dass der Abbau der noch einigen Pfeiler ohne Schaden von Erdoberflache durchgefuert werden kann, wenn das perfekte Vollfuellen nach dem Abbau und die sorgfaltige Aufsicht fuer die Deformation des Gebirges gemocht werden. 1. INTRODUCTION In several Japanese mines where massive ore bodies have been worked, field measurements of deformation and variation in stress in rock have been made mainly for the purpose of predicting an abnormal state of rock aiming at the safety of miners. In Yanahara mine, a great effort has been exerted to such field measurements, besides for this purpose, for the purpose of controlling the secondary mining, that is pillar-robbing, so that no damage is brought about on the surface. In this mine the "Lower Ore Body", 500 m long 500 m wide and 60 m thick at the central part of it, has been mined in the last fifteen years. On the surface of this ore body, there are many residences and rice fields filled with water from spring to summer, and the Yoshii river flows through them. Under these circumstances it may be difficult to achieve a high extraction percentage. But by robbing pillars reasonably, supported by the field measurements of deformation and stress in rocks, 67% of ore has already' been mined without causing any serious fracture of rock, and now further mining is demanded if possible. The present paper describes the details of measurements and the progress of pillar-robbing. 2. MINING The Lower Ore Body of pyrite lies 370m deep on an average from the surface. The north part of it dips at an angle of 20 degrees, while the south part is rather flat as shown in Fig. I. The country rocks are mainly diabase and clay slate. These rocks are strong, their compressive strengths and the Young's moduli being greater than 200 MN/m and 80 GN/m respectively. The ore itself is also strong, the corresponding values for it being greater than 120 MN/m and 100 GN/m respectively. The ground is intruded by dykes of quartz porphyry which is considerably weaker than the other rocks. The ground was divided into longitudinal and transverse panels, both 20m wide, and the former were denoted by EI, E2 and so on, while the latter by SI, S2 and so on. The panel S21 was decided as a permanent pillar, and ore was mined in the north and south regions of it. The primary mining was conducted in the following manner. In the north region the ore was mined in the longitudinal alternate panels by the sublevel stopping with filling, leaving the remaining panels as pillars. In the south region, however, the ore was mined in the northern half of each transverse panel by the cut and fill method leaving the southern half of it as a pillar. Fig. 1 shows the phase of the ore body at the end of the primary mining.
- North America > United States > Texas > Ellis County (0.24)
- Asia > Japan (0.16)
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)