The range of densities achievable by hydraulic placement of sand straddles the boundary between values giving acceptable potential performance and those giving unacceptable potential performance. This has led to concerns over the safety of structures using hydraulic fills, such as the artificial drilling islands in the Canadian Beaufort Sea. Liquefaction failures of hydraulically placed sand have occurred at four or more of these islands. Until recently, the factors affecting in situ density were little understood. Data obtained from several artificial islands are presented and these are used to demonstrate the overwhelming influence of method of placement on in situ density. The possible reasons for this influence and the implications for design are discussed. Recommendations are made for research that, together with conclusions drawn in the paper, should allow hydraulic fills to be used with more confidence in the future.Le domaine de variation des densites qui peuvent &tre atteintes par mise en place hydraulique du sable chevauche la limite entre une performance potentielle acceptable et une inacceptable. Ceci a cause certaines inquiktudes quant a la securite des structures utilisant des remblais hydrauliques, telles que les iles artificielles dans la mer canadienne de Beaufort. Des ruptures par liquefaction du sable mis en place par la methode hydraulique se sont produites dans au moins quatre de ces iles. Jusqu'a recemment, les facteurs affectant la densite in situ Ctaient peu compris. Les donnies obtenues sur plusieurs de ces iles artificielles sont presentees et elles sont utiliskes pour dimontrer l'influence prkpondkrante de la mithode de mise en place sur la densite en place. Les causes possibles de cette influence et les implications pour la conception sont discutees. L'on y fait des recommandations de recherches qui, combinkes avec les conclusions tirees de cet article, devraient permettre dans le futur l'utilisation des remblais hydrauliques avec plus de confiance.Mots clis : sable, remblai hydraulique, liqukfaction, essai de penktration au c8ne.[Traduit par la revue]Can. Geotech. J. 26, 453-466 (1989)
The groundwater flow pattern around the retaining structures of deep excavations affects the resultant water pressure, the active and passive earth pressure, and the piping and bulk heave potential. A published case history involving a hydraulic failure of a 15 m deep, temporary sheet piled excavation is analysed. The soil profile, assuming the same excavation geometry, is subsequently altered and analysed by numerical and simplified models of flow patterns. A detailed discussion of the results is used to develop generally applicable design concepts and to illustrate the limitations of simplifications. It is suggested that partial factors of safety should be applied to each load component and it is shown that the assumption of homogeneous, isotropic soil conditions may lead to unsafe designs. Furthermore, it is concluded that the hydrostatic boundary conditions, as well as the possibility of anisotropic permeability at depth and particularly below low permeability layers, must be considered in the design of deep excavations.
The design, installation, and performance of a berm-supported exploration structure in a dynamic ice environment is presented. Details are provided on design considerations which include horizontal ice loads, wave loads, seismic considerations, foundation characteristics and extreme temperatures. The development of specifications and installation techniques to account for these design concerns is presented. A case history is presented which includes a discussion of on-site modifications to the idealized placement technique, which were necessitated by extreme ice conditions. The success of this modified placement technique is confirmed through a review of the units performance during the drilling season, and the response of the structure to dynamic ice and drilling-related activity is examined.
Five general categories of offshore structures incorporating granular material ('islands') have been utilized in the Beaufort Sea, primarily in the 1970's and 1980's. Although each concept has generally served its purpose, there have been many issues both during construction and during operations. This paper reviews the major issues by referring to three specific case histories.
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