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Phanerozoic
SUMMARY: Erosion of a cut in stratified sandstone and siltstone over a ten year period resulted in a surface profile conforming to the zero stress contour calculated in the initial excavation. This paper shows stress contours calculated using a two-dimensional finite-element analysis and the configuration of the eroded cut, demonstrating that the calculated zero stress contour may be used to predict the equilibrium surface of the excavation. SOMMAIRE: L' erosion d' un versant d' excavation au couches greseuses et pelitiques, pendant la duree de 10 ans, a produit une surface de section correspondante à la ligne de tension egale zero, qui a se calcule pour l' excavation primitive. A cette etude se presentent les lignes des tensions egales qui ont calcule par la methode des elements finis à deux dimensions et se conclut par la forme du versant erode, que la ligne de tension egale calculatrice, peut utiliser pour la prevision de la surface d' equilibre d' excavation. ZUSAMMENFASSUNG: Die Erosion an einer von Flysch besetzten Abtragsböschung, hat in dem Zeitintervall von 10 Jahre ein Hangschnitt geschaft, das die Iso-spannungslinie null der Abtragsböschung entspricht. In der vorliegenden Arbeit werden die Spannungslinien dargestellt, die mit Hilfe der zweidimensionalen Berechnung der Finite-Elemente Methode bestimmt wurden. Von der Form der erodierten Abtragsböschung, wird die Schlussfolgerung gezogen, dass die berechnete Spannungslinie null, fuer die Vorbestimmung der standsicheren Abtragsflache benutzt werden kann. INTRODUCTION Unstable regions in rock slopes may be identified through negative minor principal stresses (Bukovansky-Piercy, 1975, Kalkani, 1975) because of the comparative weakness of rock under tension. In case of inclined stratified rock, such as sedimentary formations, the stress condition at the cut surface is determined by the relevant properties of the sequence of layers. A two-dimensional finite-element method incorporating the plane strain assumption and uniformely stressed triangular or quadrilateral elements has been employed for the analysis. Contours of constant stress in the new excavation were derived from these calculations for 2:1 slopes cut in sandstone and siltstone strata. The actual contour of the surface of the cut was measured 10 years after excavation, and it is shown that regions where the rock was in tension have eroded away. SITE CHARACTERISTICS Two cases of excavation for road construction are examined in this study. The road was excavated in a series of Flysch near the Kastraki Hydroelectric project in Greece. The Flysch for this area consists of interbedded sandstones and siltstones of the middle Eocene to the early Miocene. The rock types appearing at the road are weathered siltstone overlying sandstone, which in turn overlies siltstone. The weathered siltstone is light grey and calcareous and contains thin layers of fine grained sandstone. When considerably weathered it is characterized as overburden. The sandstone is grey, possessing a dence texture and contains a few scattered layers of grey shale. The siltstone is grey with fine seams of sandstone, and becomes light grey and friable when exposed. The road excavation cut the flysch series in all directions, and an upslope and a downslope section selected for study are shown in Figures 1 and 2 respectively. In both cases, the cut was at a 2:1 (vertical: horizontal) slope. During the first year after excavation was complete the slope retained its original shape, but shortly afterwards it begun to approach a more stable condition. EXCAVATION STRESSES The excavation stresses were calculated with a two-dimensional finite-element stress analysis. The minor principal stress plots are presented in Figures 3 and 4, which correspond to Figures 1 and 2 respectively. The elevations and distances in Figures 3 and 4 are given in fractions of slope height H from the toe of the cut, while the minor stress σ3 distribution is given in ratios σ3/γh where γ is the average unit weight of the rock. The following properties are used based on values of the same rock at the nearby hydro-electric project: Poisson's ratio 0.20, Modulus of elasticity 1.40E06, 1.60E06, and 2.00E06 in tons per square meter for overburden, sandstone and siltstone respectively; average unit weight 2.60 tons per cubic meter; and ambient stress coefficient equal to 1.00. The material layers are considered parallel to the ground surface. The top layer is overburden, the middle layer is sandstone and lower layer is siltstone. Excavation in Figure 3 results in a narrow tensile stress region along the cut face which widens at the lower siltstone region. In Figure 4, tensile stress regions are formed with smaller widths at the sandstone and larger widths at the siltstone. Cross sections in Figures 5 and 6 show the actual profiles of the slope cuts corresponding to the photographs.of Figures 1 and 2. The excavated slope has reached an equilibrium and the minor principal stress at the surface is zero. This final configuration is compared with the zero stress line of Figures 3 and 4.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (1.00)
SUMMARY: Studies conducted to determine the influence of mineralogy and moisture redistribution on the weathering behaviour of illite-bearing Lower-Triassic mudrocks, reveal the paramount importance of the rock material properties. The free swelling characteristics and durability of these mudrocks are probably influenced to a far greater extent by textural (fabric) parameters than by the mineralogy. Long-term strain measurements provide evidence of important anisotropic, differential swelling and shrinkage strains developing in mudrocks of a low durability when these are subjected to moisture redistribution as a result of fluctuations in the environmental humidity, alternating cycles of wetting and drying and prolonged periods of intensive air drying followed by moisture absorption. RESUME: Des etudes effectuees en vue de determiner l'influence de la mineralogie et des modifications de l'humidite environnante sur le processus d'alteration des argilites du Trias inferieur contenant de l'illite ont demontre l'importance primordiale des proprietes des composants de la roche. Les caracteristiques de gonflement et la duribilite de ces argilites sont probablement plus largement influencees par la texture que la mineralogie. Des mesures de deformation à long terme ont indique la presence de deformations importantes anisotropes et differentielles dues au gonflement et"au retrait dans des argilites à faible durabilite lorsque celles-ci sont soumises d'une part à une modification de leur humidite due aux fluctuations de l'humidite environnante, et d'autre part à des cycles alternes d'imbibition et de sechage ainsi qu'à des periodes prolongees de sechage à l'air intensif suivies d'absoption d'eau. ZUSAMMENFASSUNG: Untersuchungen ueber den Einfluss der Mineralogie und des Feuchtigkeitsgehaltes auf das Verwitterungsverhalten von Illithaltigen Tonsteinen der Unteren Trias, zeigen die ausschlaggebende Bedeutsamkeit der Materialeigenschaften der Gesteine. Die Schwelleigenschaften und die Bestandigkeit dieser Tonsteine sind vermutlich von gefuegekundlichen Faktoren wesentlich starker beeinflusst als von der Mineralogie. Langzeitige Dehnungsmessungen erbrachten den Nachweis von bedeutenden anisotropen differentiellen Schwell und Schrinkdehnungen welche sich in Tonsteinen geringer Dauerhaftigkeit entwickeln wenn diese Feuchtigkeitsumlagerungen als Folge von Fluktuationen der Umwelt Feuchtigkeit, zyklischer Benetzung und Trocknung und ausgedehnten Perioden intensiver Lufttrocknung mit nachfolgender Feuchtigkeitsaufnahme ausgesetzt sind. 1. INTRODUCTION The study of the weathering behaviour of mudrocks presents a special problem due to their wide range of engineering properties, particularly that of durability (Deere and Gamble 1971; Olivier 1979). Rock durability is a significant time-dependent factor in the weathering and disintegration of mudrocks after exposure. The presence of rock types of a low durability can lead to construction problems in both underground and surface excavations if timely preventive measures are not taken (Bieniawski, 1973; Kidd et al., 1974). Olivier (1976) is of the opinion that any engineering assessment which seeks to classify mud rock durability on a quantitative basis, must incorporate parameters which are relevant to the time-dependent weathering behaviour and the actual weathering mechanics of such rock types. This paper deals with the more important aspects of the studies carried out to determine the influence of mineralogy and moisture redistribution on the weathering behaviour of the "non-expandable" Lower-Triassic Beaufort mudrocks exposed in sections of the Orange- Fish Tunnel works (Olivier, 1976) and the author considers that these findings are also applicable to the weathering mechanics of other mudrocks of a similar mineralogical composition. The main objective in the assessment of moisture redistribution was to determine the influence of:Moisture absorption and humidity fluctuations, both of which occurred in the tunnel; and Prolonged periods of intensive air drying, which were encountered in some sections of the tunnel and in the construction shafts and surface excavations for the tunnel appurtenant works. The 82 km long, 5,3 m internal diameter tunnel was constructed for the Department of Water Affairs by conventional methods under a depth-of-cover varying from 30 m to 400 m, in the north-eastern Cape Province of the Republic of South Africa. The tunnel serves to divert water from the Hendrik Verwoerd Dam in the Orange River to the upper reaches of the Great Fish River (Kidd et al., 1974; Kidd, 1976). As the permanent concrete lining was placed some three to four years after the excavation, the weathering and deterioration of the mudrocks with time, particularly those of a low durability, caused extensive fretting and spalling of the thin skin of exposed rock in those tunnel sections where timely preventive measures had not been taken. 2. PREVIOUS STUDIES ON THE WEATHERING MECHANICS OF MUDROCKS Taylor and Spears (1970) emphasise the importance of the reversible process of intra-particle swelling for the short-term chemical weathering of "expandable" mudrocks. This involves the uptake of water within the crystal lattice of the swelling clay minerals, appreciable quantities of which are contained in such rocks. They, however, consider the initial breakdown of the "non-expandable" mudrock types of the British Coal Measures, which consist mainly of stable-lattice clay minerals (illite and kaolinite) and detrital quartz, to be caused by the irreversible physical weathering mechanism of air breakage (slaking).
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (1.00)
- Geology > Mineral > Silicate (1.00)
SUMMARY: In the paper the character of the downhill movements of slopes composed or fractured black shale of the Idrija ore deposit are discussed. The rather deep slope creeping involving a volume of some Mil m of rock masses can be attributed partly to centuries activity of mining and partly to the topographic tectonic and morphologic conditions of the broader area of the mine deposit. RESUME: L' article traite des mouvements descendants des pentes de schiste argileux noir decompose dans la region des depots d'Idrija. Le coin de glissement assez profond d' une masse rocheuse de quelques millions m peut être attribue partiellement aux effets seculaires des travaux miniers et partiellement à l'inconformite topographique, tectonique et morphologique de la vaste region du depot minier. ZUSAMMENFASSUNG: In dem Beitrag ist der Charakter des talseitigen, langsamen Deformationsprozesses, entwickelt im stark geklufteten Schiefer im Bergbaugebiet von Idrija, behandelt. Verhaltnissmassig tiefgreifendes Böschungskriechen, umfassend mehrere Millionen m von Erdmassen, ist teilweise durch hundertjahrige Bergwerksarbeiten und teilweise durch topographische, tektonische und morphologische Formen des weitausreichendes Bergbaugebietes bedingt. 1. GENERAL DATA ON THE IDRIJA MERCURY ORE DEPOSIT There are few mines where ore has been extracted continuously· for nearly 500 years. One of these is Idrija (Yugoslavia) where mercury ore was discovered as early as 1490 (Drovenik, Mlakar,1971). First carboniferous shale containing native mercury was extracted from the surface, then in 1500 under, ground mining was started. As early as 1508 rich cinnabar ore was discovered and the extent of this ore body prompted the miners to go underground. According to the basic geological data of the Idrija ore deposits (Mlakar 1959, 1969) there are the following ore containing Paleozoic and Triassic strata: black argillaceous shale and gray quartz sandstone of the Upper Paleozoic and gray and black dolomite of the Upper Permian. The black argillaceous shale and the lenses of quartz sandstone with sandy micaceous dolomite are without doubt the two oldest rocks in the mining area of Idrija. Both of them are composed of grains of quartz, chalcedony, plagioclase, epidote and mica, and bounded by quartz. They contain the most ore wherever they are in direct contact with rich ore bodies in the Triassic beds. The Upper Permian dolomite is interbedded with layered and calcerous shale. It has a fine grainy structure with xenomorphic and hypidiomorphic crystals of dolomite, detritic grains of quartz and some grains of pyrites. The dolomite is followed by calcereous micaceous shale and siltstone with lenses of öolitic limestone. The ore content depends upon contacts between individual formations and tectonic faults. The first important tectonic evolution was in the middle Triassic period. The radial movement of rock was accompanied by magmatic activity. Following this the much more intensive tectonics of the Old Tertiary period greatly effaced the effects of the tectonic evolution of the Middle Triassic era. The nappe planes from the Old Tertiary period were the final stage in the deformation of a large overthrust. In the last stage of the Alpine orogenesis the ore deposit was uplifted and cut across also by a system of faults in the Dinaric direction. (Mlakar, 1964). The moved strata were being faulted, foulded, thrusted and fissured. A schematic geologic section of the ore deposit (after I. Mlakar and M. Drovenik, 1971) is given in Fig. 1. The extraction of the ore varied according to the ownership of the mine and also to the current price of mercury. For example, in 1880 the ore deposit was opened by six shafts with a total depth of approx. 1.350 m and by two tunnels being altogether over 2.000 m long with length of tracks of approx. 22.000 m (Mohorič, 1960). The annual amount of ore excavated 'was a that time about 3.400 m from an excavated area of approx 1.700 m. Displaced material from the exploratory shafts and also the soil and chrushed rock excavated from several areas was used for packing. The last decade saw production reached 240.000 to 250.000 tons per year. In 1786 the Delo shaft (marked JD in Fig. 1) began to be built. The Delo shaft has an elliptical cross section with axes 5 m and 2.5 m. One half of the shaft area is taken up by transportation equipment whereas the other half is used for servicing the pit. The shaft runs in a protection pillar which, at the lowest elevation - 33, has an area of 44.000 m and at the surface (elevation +349) is 7.000 m. The ground plan is in the shape of an octagon with uneven sides and the limit planes incline 800 towards the horizontal. Although the shaft was protected by this pillar, with the time mining activity, being carried out close to it, caused damage along its depth and damage to the buildings on the surface and to the surroundings.
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.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.45)
SUMMARY: The features of the subsidence and horizontal displacement caused by mining coal seams are studied by examining the results of measurement of them carried out in many Japanese coal mines which have not been made open to the public. It is found that the distributions of subsidence and so on forecast by pre calculation using the method developed in Germany do not exactly coincide with the measured ones, especially in case of inclined seams. Subsequently the mechanism of subsidence is investigated by means of mathematical simulation in consideration of those features, and the method of pre calculation above mentioned is so modified that it affords good results when it is applied to the case of inclined seams. RÉSUMÉ: En utilisant les resultats inedits des mesurages executes dans les nombreuses mines de houille au Japon, I'auteur etudie les caracteristiques de l'affaissement du sol et celles du deplacement horizontal causes par l'extraction des couches de charbon. En examinant ces donnees, l'auteur trouve que la r partition des affaissements du sol prevue par le calcul utilisant la methode mise en valeur en Allemagne ne correspond pas exactement a la realite, surtout quand il s'agit des couches inclinees, L'auteur tient compte de ces caracteristiques pour etudier en suite le mecanisme de l'affaissement du sol; pour conclure il corrige la methode de calcul mentionnee ci-dessus de telle facon qu'elle donne de bons resultats quand il s'agit d'une couche inclinee egalement. ZUSAMMENFASUNG: Die Eigenschaft der Bodensenkung und der horizontalen Verschiebung, die der Abbau des geneigten Kohlenflözes verursacht, wird dadurch erforscht, dass man die Messergebnisse von ihnen prueft, die durch Vermessungen in vielen japanischen Kohlenbergwerken gewonnen waren und die nicht veröffentlicht waren. Es ist sich herausgestellt, dass die mit demin Deutschland entwickelten Verfahren vorberechnete Bodensenkungsverteilung mit den aktuellen Messergebnissen nicht genau çbereinstimmt, besonders beim geneigten Kohlenflöz. Dann wird die Zusammenhang der Bodensenkung mittels mathematischen Vorschuetzung in Beruecksichtigung ihrer Eigenschaft untersucht, und das oben genannte Verfahren der Vorberechnung wird so abgeandert, dass es gute Ergebnisse gewahrt, wen es fuer das geneigte Kohlenbergwerk angewendet wird. 1. INTRODUCTION The coal measures in Japan consist of sandstones, shales, conglomerates and coals of Palaeogene period, and are younger than those in many foreign countries. Most coal seams incline at angles less than 30 degrees. In almost all coal mines, coal seams have been mined by the longwall method. In the northern district of Kyushu, subsidence damages caused by mining coal seams had been a problem since several decades ago. After the world War II, they pre calculated the surface subsidence in many coal mines by the method developed in Germany for the purpose of investigating some possible way to minimize damages. This method of precalculation assumes that the subsidence at an optional point on the surface can be estimated by continually multiplying the thickness of extraction by the three factors, the subsidence factor, the influence factor and the time factor. The influence factor depends upon the mined area and its relative position to the point considered on the surface. The influence factor at a point on the surface will necessarily be unity if the critical area with respect to the point is completely worked. Let us call this method of precalculation the influence factor method in the present paper. Though subsidence had been precalculated for years in Japanese Coal mines, it has not been clarified to what extent the calculated Subsidence is near the actual subsidence, because no correlation between the calculated and measured values of subsidence has been made. Nowadays all coal mines in Kyushu except three undersea coal mines have closed, and of late the authors obtained fortunately the results of subsidence measurement carried out in many coal mines through the courtesy of several mining companies and the Mine Safety Bureau. On the basis of these subsidence data, they have carried out investigations into the phenomena of subsidence to clarify their features and mechanism and to find a convenient method of precalculation for them. 2. SURFACE SUBSIDENCE IN JAPANESE COAL MINES 2.1 Method of measurement In many coal mines in Kyushu, surface subsidence was measured continuously by the technique of survey, subsidized by the Ministry of International Trade and Industry. In a few mines, horizontal displacement was also measured. The stations for survey were set at intervals of from 20 to 30m over sufficiently wide ranges along two lines, AA' and BB', on the surface of each mining area. If the surface condition allowed, these lines were laid through the center of the mining area, the one running in the direction of strike, and the other in the direction of dip. The stations were constructed rigidly so as never to be destroyed. The survey was generally carried out every month from a little time before the start of mining to the stage when subsidence has almost finished.
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
SUMMARY: One of the lines of the Underground in Praha leads with two tunnels beneath a speedway. The rock massif consists of clayey and silty Ordovician shales which are weathered at the surface. The tunnels are driven by means of explosives and the overburden up to the surface of the speedway is 8 m. The breast is divided vertically into three parts and the highest is excavated by pneumatic hammer. The blasting operations were performed during full traffic on the speedway, on which neither fissures nor deformations occurred. RESUME: Une des lignes du metro de Praha avec deux tunnels est menee sous une autoroute. Le massif rocheux est forme par les schistes argileux et silteux de la formation ordovicienne et les schistes sont decomposes vers la surface. L'abattage est realise per les sautages et la surcharge est 8 m. La front etait divisee selon l'hauteur en trois parts dont la plus haute etait abattee par la main. Le trafic sur l'autoroute n'etait pes interrompu pendant les sautages et sur l'autoroute aucune fissure ou deformation ne se sont pes produits. ZUSAMMENFASSUNG: Eine Strecke der Prager U-Bahn lauft mit zwei Tunneln unterhalb der Autobahn. Das Gebirge besteht aus ordovizischen Ton - und Schluffschiefern, die an der Oberflache verwittert sind. Die Tunnel wurden mit Hilfe von Sprengungen ausgebrochen, webei das Hangende 8 m betragt. Die Brustwurde bei dem Ausbruch in drsi partien nach der Höhe eingeteilt und die höchste Partie wurde mit Ausbruchhammern ausgebrochen. Der Verkehr auf der Autobahn blieb wahrend der Sprengarbeiten ununterbrochen und auf der Autobahn sind keine Risse sowie keine Deformationen entstanden. 1. Introduction One line of the Underground in Praha goes below the speedway which is crossed by both tunnels at an angle of 36°. The distance between the top of the tunnel and the surface of the speedway is 8 m. As the tunnels are driven by blasting, it was necessary to determine the allowable charges so that the speedway in full traffic would not be damaged. Also any deformations of the speedway surface should be prevented. Otherwise, the tunnels are not driven simultaneously but with a longer time delay. 2. Construction of the speedway A section of the speedway is given in Fig. 1. The surface layer consists of asphalt concrete, the following 2 layers of 8 mixture of loamy sand and cement, a layer of loam and the lowest layer of compacted sandy gravel. The thickness of the whole is 14 to 78 cm. The underlying rock are weathered Ordovician shales, Fig.l. 3. The advance of driving The tunnels of the Underground are also driven in the Ordovician shales, which in the lower part of the tunnels pass into a less weathered rock. The shales are clayey or silty and are substantially fissured. The driving is performed using explosives and the cavity is secured by tubings. The step in one blasting - operation is 1 m and the space between the rock and the inserted tubing is grouted. For the prognosis of the seismic effects and the determination of allowable charges were used the data obtained by the author in the course of foregoing measurements of the seismic effects of blasting on the pavements, especially during the driving of the Underground below the streets of Praha. An asphalt pavement is able to bear a velocity of vibrations 50 mms-¹ without damage. According to the result, the blasting operation of the middle part is adjusted and is excavated in the second phase. The upper part is excavated without blasting. This arrangement prevents the origin of major overbreaks, which otherwise could appear in the zones of disturbance. At explosions a time - delay blasting is applied and the contour of the lower part is secured by cushion - blasting. The plan of the charges at the breast is given schematically in Fig.l. At the construction of the first tunnel the lower part was blown with maximum partial charge for a time - degree ~ 0.4 kg, the whole charge was below 7 kg. Blasting of the middle part was performed with a max. partial charge of 0.2 kg and the whole charge was 2.0 to 2.5 kg. The intensity of Vibrations, expressed by their velocity, should not exceed 30 mms-l under those conditions. 4. The control of seismic effects and deformations The vibrations caused by blasting at the first tunnel were measured at a number of explosions on the surface of the speedway, using several standpoints. The results are drawn in Fig. 2-a for the measurement recording the seismic effects of greatest intensity. It can be observed that the velocity of vibrations at the blasting of the lower part of the breast was a little smaller than the value presumed by the prognosis and reached 22 mms-¹ at the vertical component in the epicenter.
SUMMARY: This paper describes a comprehensive program of geotechnical monitoring for a 5.64 m. (18.5 ft) diameter machine mined tunnel in a highly stressed underformed dolostone. The 2490 m (8172 ft) long tunnel passes under urban Rochester, New York with rock cover varying from 1.0 m (3 ft) to 7.0 m (23 ft). Measured in-situ horizontal rock stresses were in the range of 1.3.8MN/m (2000 psi). Observed rock movements include up to 40 mm. (0.75 in.) convergence at the springline and 0.4 mm. (0.016 in) heave in the crown. Rock behavior included invert and crown spalling plus horizontal cracks at the springline. Two dimensional finite element analyses suggest that rock movements were controlled by the peak and post-failure discontinuity shear stiffness. Contractual arrangements for conduct of geotechnical monitoring programs are discussed. 1. INTRODUCTION 1.1 Project Description The Genesee River Interceptor Southwest is a 2490 m. (8172 ft) long by 4.88 m.(16 ft) finished diameter storm and sanitary sewage storage tunnel. The project, which is located in Rochester, New York (Fig. 1), was constructed entirely within a crystalline dolomite known locally as the Lockport Dolomite Formation. Depth from ground surface to tunnel invert varies from 10.7 m. (27 ft) to 22.9 m. (58 ft) with an average of approximately 12 m. (39 ft). Rock cover above the crown varies from minimum of approximately 1 m. (3 ft) to a maximum of approximately 7 m. (23 ft). Except for shafts and short lengths of tunnel adjacent to shafts, the tunnel was excavated with an 5.64 m. (18.5 ft) diameter tunnel boring machine (TBM) manufactured by the Robbins Company. The average rate of tunnel advance was 210 m. (690 ft) to 230 m. (750 ft) per month, working 3 shifts per day, Monday through Friday. Rock support in the machine-driven tunnel consisted of steel rings and rock bolts with steel strapping and a limited amount of wire mesh. Contract provisions required installation of steel ribs in areas of minimum rock cover, i.e. approximately 550 m. (1800 ft) of tunnel. Outside of these areas rock support consisted of 1.83 m. (6 ft) bolts installed 1.2 m. (4 ft) to 1.5m. (5 ft) on center. Depending on conditions encountered as the tunnel progressed, the rock bolting was supplemented with longitudinal steel straps and occasionally with wire mesh in areas where rock spalls could drop from the crown. 1.2 Geology The Rochester area lies within the physiographic province of the Lake Ontario Plain and near the northerly fringe of the Allegheny Plateau (Fig. 1). The bedrock consists of a several thousand foot sequence of early paleozoic sedimentary rocks overlying precambrian basement. The sedimentary rocks consist of shales, limestones, dolomites and sandstones which formed in shallow seas of Ordivician- Silurian period. Since Devonian time, the region has been uplifted and exposed to weathering and erosion up through the present time. It is estimated that about 610 m. (2000 ft) of bedrock has been removed by erosion exposing the present outcrops in the area.
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)
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- 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: Geotechnical investigations with in situ tests have been carried out for finite element solutions of two underground caverns located in the eastern part of the Andes in Peru. The finite element analysis have been applied for a rock mass with heterogeneities and a network of discontinuities. The first part presents a brief description of investigating methods with the obtained results, the second part presents the conception and steps of the finite element analysis of jointed rock mass tor the given problem and the obtained results. RÉSUMÉ: On a fait une appreciation de la reconnaissance geotechnique avec les essais "in situ" pour l'analyse statique des cavernes souterreines de deux usines hydro-electriques localisees dans la partie orientale des Andes au Perou. L'analyse etait realisee par la methode des elements finis pour un massif rocheux penetre des surfaces de la discontinuite. Dana la première partie il y a des methodes et des resul tats de la reconnaissance, dens la seconde partie on publie la scematisation des resultats de la reconnaissance, la conception et le procede de la solution statique et les resultats obtenus. ZUSAMMENFASSUNG: Es wurde eine Auswertung geotechnischer Untersuchung mit den Versuchen "in situ" fuer statische Beurteilung unterirdiacher Hohlraume zweier Wasserkrattwerke, die im östlichen Teil von Anden in Peru liegen, vorgenommen. Die Berechnung wurde mittels der Methode der finiten Elemente fuer ein durch Diskontinuitatsflachen durchgesetztes Gebirgsmassiv durchgefuehrt. Im ersten Teil werden Methoden und Erkundungsergebnisse angefuehrt, im zweiten teile legt man eine Schematisierung der Erkundungsergebnisse, die Konzeption und das Verfahren statischer Lösung und erzielte Ergebnisse vor. 1. Introduction The geotechnical site investigations have been carried out tor two water powerplant units at Machu Picchu and Mantaro III (Central Hidroelectrica Restitucion). The Machu Picchu water powerplant should enlarge the existing capacity from 40 MN to 110 MN in a new cavern located only about 25m from the existing one. Hereby, the water intake tunnel passing in a length of 3320 m the Vilcanota river meander with the well-known Inka town of Machu Picchu would be fully exploited. In order to increase the hydroelectric plant capacity new sand traps will be constructed as well as a new penstock, a new cavern and a new tailrace tunnel. The new cavern will be 46 m long and 28 m high with the width ranging from 18 to 22 m (the cross section area F ± 550 m2). The Mantaro III water powerplant should have followed the Mantaro I and II powerplants, thus using the tailwater trom the 7 turbines of 800 MW total output in the 240 m remaining head offered by the wide meander of the Mantaro river between the village Kichuas and the mouthing of the Colcabamba river. Here, two caverns should be constructed side on side, one for the powerplant and the other for the switchyard. The larger cavern will be 104.5 m long and 22 m wide with a height of 34.5 m (the cross section area F ± 730 m), the smaller one will be 88 m long and 13 m wide with a height of 18 m (the cross section area F ± 230 m). The proposed axes distance between both Mantaro caverns is 46 m. 2. Program of Geotechnical Investigations At both sites, the caverns will be located at the foot of the high Andes valley slopes; at Machu Picchu on the level of 1750 m and at Yantaro IlIon the level of 1560 m. The Machu Picchu cavern will be located 40 - 86 m from the exploratory gallery entrance thus having a 65 - 140 m rock mass cover (the slope dip is about 580), the Mantaro III caverns will be located 150 - 250 m from the exploratory gallery entrance thus having a 190 - 280 m rock mass cover (the slope dip is about 500). In both cases, the location of the caverns have been favourable due to the local geological conditions. The caverns at Kechu Picchu are thus located in granodiorites and granites of a great batholite on the central part of the Vilcanota river, presumably of the Devon origin. The caverns at Kentaro III are located in a granite batholite named Villa Azul, presumably of the Upper Cretaceous origin. As the entire complex ot the Andes is affected by epeirogenetice movements, the rock mass is affected tectonically of various intensity with a tectonical and thermal alteration of some rock minerals. Besides, at Mantaro III the genetic reverberations represented themselves by the outcoming of mineral springs and the outburst of gases into the exploratory galleries. The tectonic expressions of various age as well as the expected concentration of stresses at the foot of the high valley slopes with exfoliation fractures near the slope surface has given a requirement to apply FEM programs respecting the existing joint systems and fault zones in the design solutions.
- Europe (0.94)
- South America > Peru (0.81)
- Geology > Structural Geology > Tectonics > Compressional Tectonics > Fold and Thrust Belt (0.54)
- Geology > Rock Type > Igneous Rock > Granite (0.45)
SUMMARY: Tests were carried out on samples of a blue marly rock in the context of a soil investigation at the site of a deep highway cut. The results of these tests are presented and discussed. The main observations are that the blue marl was strain softening, exhibiting an almost brittle behaviour, that saturation resulted in a large reduction of the peak strength: and that despite the wide scatter of the test results, as a general trend, strength values increase with an increase in overburden and a decrease in void ratio and water content. RESUME: Dans le cadre d'une recherche congernant l'etude des problèmes associes à une excavation profonde pour une construction routière, un nombre d'essais a ete execute sur des echantillons de marne bleue. On present les resultats de ces essais et on procède à une brève discussion de leurs caracteristiques. Les essais ont montre que la marne bleue se caracterise d'un comportement du type "strain softening", avec une fragilite importante. La saturation de cette marne conduit à une grande reduction de la resistance de "pic". Malgre la dispersion notoire des resultats experimentaux, on se conduit à l'etablissement d'un aspect qualitatif de ce comportement; la resistance accroit lors de l'augmentation de l'epaisseur de la couche superposante (overburden) et la diminution de l'indice des vides et de la teneur en eau. ZUSAMMENFASSUNG: Im Rahmen einer bodenmechanischen Untersuchung eines Autostrassenschnittes, wurden Versuche in blauen Mergelstein ausgefuehrt. Es werden die Versuchsergebnisse gegeben und kritisiert. Als Hauptbemerkungen der Ergebnisse sind dass der Mergelstein Dehnungserweichend (strain softening) und brueckelig ist, dass die Wassersattigung eine grosse Reduzierung der maximaler Festigkeit bringt, und dass trotz der breiten Verteilung der Versuchsergebnisse, die algemeine Tendenz ist dass die Festigkeitswerte mit der Vergrosserung der Überlagerungsmachtigkeit und der Abnahme der Porenziffer und des Wassergehaltes zunehmen. 1. INTRODUCTION A new highway is being built in northwestern Greece, connecting the town of Preveza with the port of Igoumenitsa. During the excavations for the highway several problems arose and several slides occurred (Cavounidis-1979). One of the problems that had to be faced was the crossing of an area, where the designed depth of the cut was more than 40 m. The excavation of such a deep cut required geotechnical investigation in order to check the feasibility of the design and to propose measures which would ensure the stability of the slopes. During the investigation it was found that the main part of the excavation would be in a thick layer of blue marly rock. Laboratory tests were carried out to determine the strength and other properties of the marl. The main results of these tests together with observations and correlations that were made are presented herein. 2. GEOLOGICAL AND MORPHOLOGICAL CONSIDERATIONS The general area is a hilly to almost mountainous part of Epirus, in northwestern Greece, a few kilometers south of the ancient Aheroussia lake and about 1 km. inland from the coastline of the Ionian sea. The upper formations are sedimentary layers of the Pliocene period. They consist of marls and conglomerates (or sand-gravels). The bedrock consists of massive limestone, cars tic and weathered in the upper part. In its cavities and on its surface there is terra rossa due to chemical weathering of the limestone. The region belongs to the Ionian zone which was folded in the late stages of the alpine orogenesis. It has faults running in a N-S or NW-S direction, that is, parallel to the Ionian coast. The joints in the Pliocene formations run N-S and NE-SW. The region has not yet equilibrated and thus earthquakes of a tectonic nature are not uncommon. It belongs to Category II according to the Greek antiseismic regulations (Royal Decree-1963) with a seismic coefficient ε= 0.06 for rocks and ε=0.08 for soils. 3. SOIL PROFILE Four boreholes were drilled by rotary drilling in the initial phase of the investigations, followed by another three in the final stage, of 282 m. total length. The investigation showed that the top part of the soil consists of a greyish brown stiff marly clay having some sand content. In one borehole much black organic material was also found. Fig. 1 shows a typical cross section of the soil as well as the level of the highway and the slopes of the cut in the initial design. 4. TEST RESULTS Laboratory tests were carried out on a large number of samples of the blue marly rock. Table I lists the average values of the Atterberg limits and the physical properties of the marl, where wL is the liquid limit, wp is the plastic limit, Ip is the plasticity index, w is the natural moisture content, Yd is the dry unit weight, Yt is the total unit weight and e is the void ratio. The degree of saturation of the samples tested varied from 80% to 100%.
- Europe > Greece (0.46)
- Europe > Norway > Norwegian Sea (0.24)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.71)
- Geology > Mineral > Silicate (0.68)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.45)