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31.
A novel three‐dimensional particle‐based technique utilizing the discrete element method is proposed to analyze the seismic response of soil‐foundation‐structure systems. The proposed approach is employed to investigate the response of a single‐degree‐of‐freedom structure on a square spread footing founded on a dry granular deposit. The soil is idealized as a collection of spherical particles using discrete element method. The spread footing is modeled as a rigid block composed of clumped particles, and its motion is described by the resultant forces and moments acting upon it. The structure is modeled as a column made of particles that are either clumped to idealize a rigid structure or bonded to simulate a flexible structure of prescribed stiffness. Analysis is done in a fully coupled scheme in time domain while taking into account the effects of soil nonlinear behavior, the possible separation between foundation base and soil caused by rocking, the possible sliding of the footing, and the dynamic soil‐foundation interaction as well as the dynamic characteristics of the superstructure. High fidelity computational simulations comprising about half a million particles were conducted to examine the ability of the proposed technique to model the response of soil‐foundation‐structure systems. The computational approach is able to capture essential dynamic response patterns. The cyclic moment–rotation relationships at the base center point of the footing showed degradation of rotational stiffness by increasing the level of strain. Permanent deformations under the foundation continued to accumulate with the increase in number of loading cycles. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
32.
Lithological controls on soft cliff planshape evolution under high and low sediment availability 下载免费PDF全文
Natasha E. Carpenter Mark E. Dickson Mike Walkden Robert J. Nicholls William Powrie 《地球表面变化过程与地形》2015,40(6):840-852
This paper addresses a series of geomorphic questions relating to large‐scale (> 1 km), long‐term (100 – 1,000 years) coastal planshape evolution. Previous research on soft‐cliff coasts has recognised the role of protective fronting beach volumes on reducing rates of cliff toe retreat. However, it is the maintenance of this critical threshold that ultimately determines two contrasting modes of shoreline behaviour: Mode A, in which there is little beach sediment and shoreline evolution is controlled by material strength; and, Mode B, when ample beach sediment means that shoreline evolution is controlled by longshore sediment transport. Here we use a numerical model (SCAPE) to investigate temporal and spatial changes in beach volume on a broader range of feedbacks than considered in previous models. The transition between Mode A and Mode B coasts is defined by relative sediment inputs to outputs and used to explore how these contrasting modes control the evolution of an initial linear frontage exhibiting longshore changes in cliff lithology (material resistance and the proportion of beach grade material in the eroded bedrock). Under Mode A, relative changes in material resistance result in long term heterogeneous rates of retreat, which result in the development of persistent headland and embayment features. However, under Mode B, feedbacks between coastal planshape, longshore sediment transport, beach volume and wave energy result in steady state retreat rates regardless of longshore variations in resistance. Results are compared and contrasted to previous simulations and site specific examples and a conceptual model of Mode A and Mode B interactions presented. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
33.
Lateglacial and Holocene relative sea‐level changes and first evidence for the Storegga tsunami in Sutherland,Scotland 下载免费PDF全文
Antony J. Long Natasha L. M. Barlow Sue Dawson Jon Hill James B. Innes Catherine Kelham Fraser D. Milne Alastair Dawson 《第四纪科学杂志》2016,31(3):239-255
34.
Douglas Mackay Emily Hathaway Nicholas de Sieyes Han Zhang Ehsan Rasa Charles Paradis Radomir Schmidt Juan Peng Timothy Buscheck Natasha Sihota 《Ground Water Monitoring & Remediation》2018,38(2):24-39
Natural source zone depletion (NSZD) refers to processes within chemically impacted vadose and saturated zones that reduce the mass of contaminants remaining in a defined source control volume. Studies of large petroleum hydrocarbon release sites have shown that the depletion rate by vapor phase migration of degradation products from the source control volume through the vadose zone (V‐NSZD) is often considerably higher than the rate of depletion from the source control volume by groundwater flow carrying dissolved petroleum hydrocarbons arising from dissolution, desorption, or back diffusion, and degradation products arising from biodegradation (GW‐NSZD). In this study, we quantified vadose zone and GW‐NSZD at a small unpaved fuel release site in California typical of those in settings with predominantly low permeability media. We estimated vadose zone using a dense network of efflux monitoring locations at four sampling events over 2 years, and GW‐NSZD using groundwater monitoring data downgradient of the source control volume in three depth intervals spanning up to 9 years. On average, vadose zone was 17 times greater than GW‐NSZD during the time interval of comparison, and vadose zone was in the range of rates quantified at other sites with petroleum hydrocarbon releases. Estimating vadose zone and GW‐NSZD rates is challenging but the vadose zone rate is the best indicator of overall source mass depletion, whereas GW‐NSZD rates may be useful as baselines to quantify progress of natural or engineered remediation in portions of the saturated zone in which there are impediments to loss of methane and other gases to the vadose zone. 相似文献
35.
A combined field,laboratory and numerical study of the forces applied to,and the potential for removal of,bar top vegetation in a braided river 下载免费PDF全文
Vegetation can have an important role in controlling channel planform, through its effects on channel roughness, and root‐reinforcement of bank and bar materials. Along the Platte River in central Nebraska, USA, The Platte River Recovery Implementation Program (PRRIP) has been tasked with managing the planform of the river to benefit endangered species. To investigate the potential use of planned short duration high flow (SDHF) events to manage bar vegetation, this study combined several approaches to determine whether flows of up to 227 m3s?1 through the central Platte River, could remove cottonwood, Phragmites and reed canarygrass stands of various ages and densities from in‐channel bars. First, fieldwork was carried out to measure the uprooting resistance, and resistance to bending for each species. Second, a set of flume experiments was carried out to measure the forces exerted on the three species of interest under different flow conditions. Finally, a numerical study comparing drag forces (driving) measured in the flume study, with uprooting forces (resisting) measured in the field, was carried out for each species to determine the likelihood of plant removal by SDHF events. Results showed that plants with more than a year of root growth, likely cannot be removed through drag and local scour alone, even at the 100‐year recurrence interval discharge. At most, a few cottonwood seedlings could be removed from bars through drag, scour and undercutting, where rooting depths are still small. The results presented here help us further understand the positive feedbacks that lead to the creation of permanent, vegetated bars rather than mobile braided channels. As such, the findings could help inform management decisions for other braided rivers, and the combined field, flume and modeling techniques used in this study could be applied to other fluvial systems where vegetation and planform dynamics are of interest. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
36.
Natural source zone depletion (NSZD) is increasingly being integrated into management strategies for petroleum release sites. Measurements of NSZD rates can be used to evaluate naturally occurring hydrocarbon (HC) mass losses, and provide a baseline for evaluating engineered recovery systems. Here, nominal saturated and unsaturated zone HC losses were quantified by groundwater sampling and ground surface CO2 effluxes approximately monthly over a 1-year period. In addition, subsurface gas profiles and temperature, precipitation, and groundwater elevation were evaluated to elucidate dominant environmental factors controlling NSZD rates. Results showed that NSZD rates estimated by surface CO2 effluxes were, on average, more than a factor of 3 greater than those estimated by uptake of electron acceptors (primarily sulfate) in extracted groundwater. This may indicate that vadose zone mass loss mechanisms (e.g., volatilization and subsequent biodegradation) were dominant in this system, but possible transfer of gases from the saturated zone to the vadose zone confounds this interpretation. Results for this semiarid site revealed that increasing NSZD rates tended to occur with increasing ambient monthly precipitation and temperature when accounting for time lags associated with subsurface transport. However, groundwater elevation was not found to be significantly related to NSZD rates. This result is counter to an expectation that increased smear zone exposure increases HC mass losses, and suggests that the pump-and-treat system did not greatly influence total NSZD rates directly through smear zone flushing or indirectly by lowering the regional water table. 相似文献
37.
Fiona J. Valesini Mathew Hourston Michelle D. Wildsmith Natasha J. Coen Ian C. Potter 《Estuarine, Coastal and Shelf Science》2010
This study has developed quantitative approaches for firstly classifying local-scale nearshore habitats in an estuary and then predicting the habitat of any nearshore site in that system. Both approaches employ measurements for a suite of enduring environmental criteria that are biologically relevant and can be easily derived from readily available maps. While the approaches were developed for south-western Australian estuaries, with a focus here on the Swan and Peel-Harvey, they can easily be tailored to any system. 相似文献
38.
Louis A. Tremblay Olivier Champeau Patrick L. Cahill Steve Pullan Natasha Grainger Ian C. Duggan 《新西兰海洋与淡水研究杂志》2019,53(1):97-112
Non-indigenous zooplankton species pose a biosecurity threat to New Zealand’s freshwater native taxa. Nine species are known to have established in New Zealand lakes to date. The spread of some zooplankton taxa is linked to the translocation of farmed fish, principally grass carp (Ctenopharyngodon idella), and recreational vessel movements. The aims of this study were to assess the effectiveness of a range of chemical and physical treatments for transport water and associated equipment to kill freshwater cladoceran, copepod, and rotifer zooplankton species, and their risk to non-target fish. Sodium chloride was the most effective and applicable chemical treatment tested at length in the cladoceran and, combined with physical treatment via mechanical filtration of water or hot water immersion of equipment (to also manage the risk of diapausing eggs), represents an effective option for the control of non-indigenous zooplankton, with limited impact on stenohaline fish. 相似文献
39.
Monika Koch-Müller Stanislav S. Matsyuk Dieter Rhede Richard Wirth Natasha Khisina 《Physics and Chemistry of Minerals》2006,33(4):276-287
The incorporation of hydrogen in mantle olivine xenocrysts from the Udachnaya kimberlite pipe was investigated by Fourier-transform infrared spectroscopy and secondary ion mass spectrometry (SIMS). IR spectra were collected in the OH stretching region on oriented single crystals using a conventional IR source at ambient conditions and in situ at temperatures down to −180°C as well as with IR synchrotron radiation. The IR spectra of the samples are complex containing more than 20 strongly polarized OH bands in the range 3,730–3,330 cm−1. Bands at high energies (3,730–3,670 cm−1) were assigned to inclusions of serpentine, talc and the 10 Å phase. All other bands are believed to be intrinsic to olivine. The corresponding point defects are (a) associated with vacant Si sites (3,607 cm−1 E || a, 3,597 E || a, 3,571 cm−1 E || c, 3,567 E || c, and 3,556 E || b), and (b) with vacant M1 sites (most of the bands polarized parallel to a). From the pleochroic behavior and position of the OH bands associated with the vacant M1 sites, we propose two types of hydrogen—one bonded to O1 and another to O2, so that both OH vectors are strongly aligned parallel to a. The O2–H groups may be responsible for the OH bands at higher wavenumbers than those for the O1–H groups. The multiplicity of the corresponding OH bands in the spectra can be explained by different chemical environments and by slightly different distortions of the M1 sites in these high-pressure olivines. Four samples were investigated by SIMS. The calculated integral molar absorption coefficient using the IR and SIMS results of 37,500±5,000 L mol H2O cm−2 is within the uncertainties slightly higher than the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003) (28,450±1,830 L mol H2O cm−2). The reason for the difference is the different distributions of the absorption intensity of the spectra of both studies (mean wavenumber 3,548 vs. 3,570 cm−1). Olivine samples with a mean wavenumber of about 3,548 cm−1 should be quantified with the absorption coefficient as determined in this study; those containing more bands at higher wavenumber (mean wavenumber 3,570 cm−1) should be quantified using the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003).
相似文献
Monika Koch-MüllerEmail: Phone: +49-331-2881492 |
40.