We present a case study that evaluates the seismic performance of a centerline tailings dam in the South American Andes through dynamic effective stress analyses with advanced constitutive models. The seismic demand at the dam site was evaluated through a probabilistic seismic hazard analysis (PSHA), which derived in deterministic and probabilistic-based seismic design criteria. The PSHA results were used to select spectrally matched ground motions for the subsequent dynamic analyses. The centerline tailings dam is planned to be raised in stages to 90 m high, which was considered in establishing the initial stresses and pore pressures before seismic loading. The material properties were based on a large geotechnical characterization program considering the mine tailings to be stored in the deposit and other critical dam components. The dynamic analyses were performed using the UBCHYST constitutive model for materials that are not expected to generate significant excess pore pressures and the PM4Silt constitutive model for the materials that may generate excess pore pressures due to cyclic loading. The results show the deformation patterns in the centerline dam, after the seismic loading, are significantly affected by the mine tailings presence. The results are useful to plan the overall operational management of the tailings facility.
Undisturbed frozen samples can be efficiently obtained using the artificial ground freezing method. Thereafter, the restoration of in situ conditions, such as stress and density after thawing, is critical for laboratory testing. This study aims to experimentally explore the effects of thawing and the in situ stress restoration process on the geomechanical properties of sandy soils. Specimens were prepared at a relative density of 60% and frozen at −20 °C under the vertical stress of 100 kPa. After freezing, the specimens placed in the triaxial cell underwent thawing and consolidation phases with various drainage and confining stress conditions, followed by the shear phase. The elastic wave signals and axial deformation were measured during the entire protocol; the shear strength was evaluated from the triaxial compression test. Monotonic and cyclic simple shear tests were conducted to determine the packing density effect on liquefaction resistance. The results show that axial deformation, stiffness, and strength are minimized for a specimen undergoing drained thawing, restoring the initial stress during the consolidation phase, and that denser specimens are less susceptible to liquefaction. Results highlight that the thawing and stress restoration process should be considered to prevent the overestimation of stiffness, strength, and liquefaction resistance of sandy soils.
One of the prime concerns in designing offshore gravel islands in ice-covered waters such as in the U.S. and Canadian Beaufort Seas is the ability of the island to resist the imposed design ice loads. In presenting this paper, the goal is to describe a methodology to aid in the preliminary assessment of the overall strength of a gravel island to resist a design ice load for a set of prescribed design and environmental parameters. Conversely, the described methodology can be used to aid in developing a preliminary island design in terms of its size, height and geometry to ensure the island had sufficient strength to resist the design ice loads. More specifically, the purpose of this paper is twofold:to describe a methodology for establishing the strength of offshore gravel islands to resist imposed ice design loads; andto use this methodology to illustrate how the performance of gravel islands to resist the imposed ice loads varies with the major design and environmental parameters. In summary the results of the analysis presented in this paper indicate that, from the standpoint of resisting ice loads, gravel islands will continue to be technically feasible offshore drilling platforms for both explorations and production in the U.S. and Canadian Beaufort Seas as the oil industry moves into deeper and more harsh areas. INTRODUCTION With the recent offshore lease sales in the Diaper Field and the future scheduled lease sales, interest in investigating various drilling platform concepts for exploration and production in the U.S. and Canadian Beaufort Sea areas has continued. Proposed concepts have ranged from gravel islands, caisson retained islands, and mobile structures to moored floating platforms. To date gravel islands have been used as the primary man-made exploration drilling platform in the U.S. and Canadian Beaufort Seas. As interest has expanded to areas farther from shore, deeper water and less protected areas, the question arises as to whether or not gravel islands will continue to be viable and will they have sufficient strength to resist the imposed design ice loads. In designing gravel islands for the Beaufort Sea it is important to note that other major concerns must be considered in addition to the island strength to resist ice loads. These other concerns include: ice ride-up/ pile-up potential; wave run-up and overtopping; seabed scour due to ice, waves and currents around the structure; and slope protection to prevent island erosion by waves and ice. Of these, however, ice loads tends to be one of the major concerns and is the focus of this paper. GRAVEL ISLAND STRENGTH DETERMINATION Overview In determining the overall gravel island strength to resist the design ice load, three failure modes were considered: failure at the freeze front, failure at the ice loading plane, and failure at the gravel fill/ silt interface which may be at the seafloor or lower if surface silts are dredged before construction. For the range of soil material properties investigated (see Table 1) the governing failure mode was primarily a function of the depth of freeze as depicted in Figure 1.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.