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Equinor is ramping up production at its Snorre B platform in the northern North Sea following a precautionary shut-in prompted by an earthquake in the area. The quake had an estimated magnitude of 4.6 on the Richter scale, according to the Norwegian National Seismic Network and was centered in the North Sea between Stad, off the Norwegian coast, and the Faroe Islands. The earthquake is reported to have been felt from the whole of western Norway all the way south to Jæren and eastward in Drammen. At the time of shut-in, Snorre B was producing between 30,000 and 35,000 BOPD. An Equinor spokesman told Reuters that Snorre was the closest in proximity to the earthquake and, on the installations, they felt the earthquake, but there were no reports of any damage to installations or on the seabed.
Abstract The influence of bucket spacing has been studied for either static capacities or cyclic capacities of symmetry multi-bucket foundation on soft clays strata. The changing law for adjustment parameter of vertical (horizontal) static capacities and cyclic capacities for different bucket spacing has been analyzed. The vertical (horizontal) static capacities of twobucket and four-bucket foundation have been calculated though three-dimensional finite element analysis, and a method has been suggested to determine vertical (horizontal) static capacities for symmetry multi-bucket on soft clays strata. Further, vertical (horizontal) cyclic capacities of two-bucket foundation for different bucket spacing have been determined considering cyclic strength at 1000 times of cycles as yielding strength. Several conclusions can be obtained though analyzing the relationship between adjustment parameter of vertical (horizontal) cyclic capacities and bucket spacing as well as static loads. Vertical (horizontal) cyclic capacities are related to static loads for certain bucket spacing. Vertical (horizontal) cyclic capacities are on the peak when static is 0.23 or 0.60 times of vertical static capacities. Adjustment parameter of vertical (horizontal) cyclic capacities is the function of bucket spacing not related to static loads, and it can be substituted with corresponding adjustment parameter of static capacities when the bucket spacing exceeds 1.0 times of bucket diameter. Then, a practical method, verified through cyclic capacities calculation results of four-bucket, has been suggested for determining vertical (horizontal) cyclic capacities of symmetry multi-bucket foundation on soft clays strata. Introduction As a newly and moving platform, bucket foundation has been widely used in the construction of offshore oil and gas platforms since early 1990s. Because of its simplicity, reliability and cost savings, bucket foundation is specially applied to marginal offshore oil field. Studies have been done on uplift capacity and stability in subsiding for bucket foundation (Sherif EI-Gharbawy, 1999; M.F. Randolph and A.R. House, 2002). However, cyclic mechanical character of bucket foundation under static loads combined cyclic loads has not been well understood and applied, which will relate to designing and using bucket foundation in long-term ocean environment. Up to now, several approaches to evaluating capacities under static loads combined cyclic loads are as followed. One method is to set up the constitutive relations of clays with cyclic loading and then calculate cyclic capacities by elastoplastic numerical method (Prevost, 1981; Marr, W. A., 1981; Wang Jianhua and Yao Minglun 1996(in chinese)). This method can follow cyclic stress path and reflect cyclic failure course in intuitive manner. But the workload of calculation will be extremely large and calculating results will be not easy to be collectd because of calculating error are accumulated, especially in three-dimensional calculating. Andersen (1988, 1993) ever developed the method evaluating cyclic capacities on Drammen Clay. The soil element stress state along the potential failure surface and cyclic strength relationship at failure have been determined through a lot of cyclic triaxial and cyclic simple shear tests using quasi-static method. Cyclic capacities are further evaluated according to limiting equilibrium theory. The disadvantage lies in simplifying the three dimensional into plane problem and conducting a large number of cyclic triaxial and cyclic simple shear tests on the same soil sample. The action of cyclic loading on foundation soils is thought the reduction of its static strength and the cyclic capacities are estimated from the r
A series of isotropica1ly consolidated undrained triaxial tests have been performed to under stand the response of an artificially cemented marine clay under static compression loading. The investigation highlights the role played by cementation on the stress-strain curve, failure strain, effective stresspath, undrained strength and Skempton's pore water pressure parameter. The results show that the behaviour of a cemented clay is strongly influenced by consolidation pressure. The paper discusses, in detail, the phenomenon of "phase transformation" and its relation to the existence of bisegmented stress-strain behaviour, typical of the cemented clay. INTRODUCTION Marine clays are often encountered with good amount of precipitation compounds like carbonates and iron oxides etc.(Bjerrum, 1973; Lefebvre & La Rochelle, 1974). These compounds induce brittle nature and cause apparent overconsolidation through chemical bonding effect This special feature in marine clays, inherited due to its mode of deposition, makes the deformation phenomenon more complex to understand. As of today, the available information dealing with naturally cemented marine clays is rather scarce and inconclusive mainly due to the non-uniform cementation and disturbances during sampling, particularly when the sample is collected from a considerable depth below the sea bed. A number of researchers, in the past, have attempted to understand the behaviour of the naturally cemented clays through artificially cemented specimens, since it allows greater control over important variables. Tavenas et al.(1973) developed a synthetic material With kaolinite, bentonite, cement and water in order to simulate mechanical properties of Champlain clays. Fischer et al. (1978) studied the simple shear behaviour of Drammen clay introducing calcium carbonate into it as the cementing agent The present study undertakes an experimental programme on an artificially cemented Indian marine clay to bringout the effect of cementation on various aspects of the stress-strain behaviour of soft marine clays under undrained loading conditions.
ABSTRACT: Characteristics of in situ rock can be estimated from the rock mechanics investigations and from the propagation and shapes of elastic waves. In recent years, besides the rock mechanic studies, seismic methods are highly used for the testing of surface and underground facilities, large dams and earthquake engineering subjects. For this purpose, a geophysical investigations (which concerns seismic-refraction and tomography studies) and rock mechanics studies (laboratory tests) are carried out at Burke dam site right bank in Adana-Turkey. In this paper, the results of field and laboratory studies are given and rock mass is classified according to seismic velocity and rock type conditions. RESUME: Les caracteristiques in-situ des roches peuvent etre esteems à partir des recherche de la mecanique des roches et de la propagation et de la found des nodes elastiques. Dans les dernieres annees, les màthods sismiques sont frequemmeut utilisees, à côte des etudes de mecanique des roches, pour tester la surface et Ie housetrain des battements, des grinds barrages et des suits dans Ie eider du genie seminude. Une etude geophysique (sismique-refraction et tomographic) et de mecanique des roches a ete menee dans la rive droite du site de barrage Burke, à Adana, Turquie. Dans cette publication, mons preseutons les resultats de terrain et des etudes de laboratoire et une classification des caracteristiques des roches seton les vitesses sismiques et des conditions de types de roches. ZUSAMMENFASSUNG: Charakteristiken von dem Feels an Ort und Stele ken man aus felsmechanischen Forschungen und von der Übertragung und Formen von elastischen Welled beurteilen. In den latten Ahrens werden nubbin felsmechanischen Untersuchungen in hohem Maße seismische Methoden fuer die Pruefung von Tagesoberflache und Untertageeinrichtungen, großen Drammen und Erdbeben Ingenieurthemen benutzt. Fur diesen Zweck wurde seine geophysische Frosting (welche seismische Refraction und tomografische Forschungen betreffen) und felsmechanische Untersuchungen (Laboruntersuchungen) an der rechten Bank des Burke Dammgelandes in Adana- Tuerkei durchgefuehrt. In diesel Ericht wurden die Ergebnisse von Fled und Laboruntersuchungen gegeben und Felsmassecharakterisierung ist gemaß zu seismischer Geschwindigkeit und Felsartzustand klassifiziert. 1 INTRODUCTION The rock mechanics studies in field and laboratory for determining the physical and geological character of the rocks and ground are widely used. Due to strict safety specifications requirement for ground and underground facilities, the seismic testing is extensively used. These methods are practical and convenient for determining a stratigraphic map and information on the geological character and mechanical properties of the rockmass. For the purpose of seismic measurements, the seismic-refraction and seismic-tomography methods are commonly used techniques. A common feature of all these methods is that information can be derived from travel times and wave-forms of a wave propagating from the shot point to the receiving point. Using only seismic-refraction data can be misleading for solution of a variety of geotechnical and earthquake engineering problems. When a rock formation with high seismic velocity overlies materials of lower velocity, seismic velocity of the beneath formation cannot be determined. To overcome this constraint, the technique of seismic tomography, similar to X-ray computer tomography measurements for reconstructing internal images of the human body, can be used. Although this technique is complex and expensive it is the only technique which can give precise two-dimensional velocity distribution through a given zone enclosed by boreholes, test adits or ground surface. This two dimensional velocity image can be interpreted in terms of a two-dimensional distribution of rock properties (ISRM, 1988). To define the rock mass classification accurately, in-situ seismic velocity investigations have to be supported with laboratory rock mechanics studies. In this study, the geophysical investigation and rock mechanical studies carried out at Burke dam site right bank in Adana- Turkey are presented (Fig. 1). Burke project includes a 201 m high, double curvature, thin, concrete arch dam being constructed on Cayman river with its height is rank as first in Turkey and eighteenth in the world in concrete dam classification. The stratigraphic map, geology and rock mass characterization of the investigated field is established under the light of seismic and rock mechanics investigation.
ABSTRACT: Brief history of Rock Mechanics and dam foundation design. The number of embankment dams built on rock foundation is comparable to that of concrete dams (the most frequent type of very large dam built on rock foundations). Above and beyond investigation methods, mechanical analysis and foundations treatment, the quest for impermeability remains an essential question, and is dealt with by the defensive measures against internal erosion, in the form of filters and regularly maintained drains, together with monitoring of water levels and pressures. RESUME: Rappel historique sur la Mecanique des Roches et les fondations de grands barrages. Importance comparable des barrages en beton (preponderants dans les grandes hauteurs) et des barrages en remblais fondes au rocher. Par delà les methodes de reconnaissance, d"analyse mecanique et de traitemant des fondations, la recherche de l"etancheite reste une question primordiale qui a recueilli la majorite des communications à ce Workshop. Elle doit s"accompagner de masures de defense contre l"erosion" interne, par des filtres et drains regulièrement entretenus, completes par une surveillance piezometrique. ZUSAMMENFASSUNG: Es wird ein Überblick gegeben ueber die Felsmechanik sowie ueber den Entwurf von Talsperrengruendungen. Ein Vergleich wird angestellt zwischen auf Fels gegruendete Schwergewichstmauern und Drammen. Neben Erkundungsmethoden und der Durchfuehrung von Berechnungen zur Untersuchung des machanischen Verhaltens des Gruendungssystems von Talsperren sind Fragestellungen zur Abdichtung des untergrundes von grundlegender Bedeutung und werden in den maisten Beitragen zum Workshop behandelt. Es werden dabei Maβnahmen gegen das Auftreten deer inneren Erosion vorgestelt,zwie z.b. die Ausbildung von Filtern und Drainagen sowie die Durchfuehrung von piezometrischen Messungen. 1. HISTORICAL BACKGROUND Foundations were a matter dealt with in the very first congresses of "the International Commission on Large Dams: in 1933 Question 2b looked at infiltration of water, and in 1936 Question 6 dealt with geo-technical studies of foundation materials. In 1964, at the eighth ICOLD Congress in Edinburgh, Question 28 dealt specifically with the question of the physical and mechanical properties of rock in situ. And at the following Congress, in Istanbul in 1967, Question 32 looked at the view of the foundation. Rock mechanics, a new discipline of interest in the construction of large dams, was then fast developing. At, the first ISRM congresses, in Lisbon in 1966, and then in Beograd in 1970, more than half of the topics proposed directly concerned dam engineers for they dealt with the exploration, description, and properties of in situ rock of different kinds, as well as with its performance as a structural foundation. In 1970 too, the first congress of the International Association of Engineering Geology was held. This new discipline Introduced quantitative aspects to geology, a science that had until then been predominantly a natural science. Engineering geology is also of direct relevance to dam building. In its second Congress, in Sao Paulo in 1974, the association specifically devoted one topic of discussion to dam foundations. The sixties and seventies were a rich training ground for better mastering the problems associated with the rock foundations of dams. Just before the third ISRM Congress in Denver, in 1974, a masterful state-of-the-art paper was prepared by Pierre Londe, now Honorary President of ICOLD: it was entitled "Rock Mechanics and Dam Foundation Design" (ICOLD, 1973). There must be around 3,000 dams more than about fifty metres high, roughly half, of which are embankment dams (earth and/or rockfill), the other half being concrete dams. The proportion of concrete dams increases with the height of the dams considered, as does the proportion of arch dams among the concrete dams.