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Experimentally determined spatial patterns of soil redistribution across a break in slope derived using 10 rare earth element (REE) oxides as sediment tracers are presented. An erosion experiment was conducted using simulated rainfall within a laboratory slope model measuring 2·5 m wide by 6 m long with a gradient of 15° declining to 2°. Soil was tagged with multiple REE and placed in different locations over the slope and at the end of the experiment REE concentrations were measured in samples collected spatially. A new method was developed to quantify the erosion and deposition depths spatially, the relative source contributions to deposited sediment and the sediment transport distances. Particle‐size selectivity over an area of net deposition was also investigated, by combining downslope changes in particle‐size distributions with changes in sediment REE composition within a flow pathway. During the experiment, the surface morphology evolved through upslope propagation of rill headcuts, which gradually incised the different REE‐tagged zones and led to sediment deposition at the break in slope and the development of a fan extending over the shallow slope segment. The spatial patterns in REE concentrations, the derived erosion and deposition depths, the relative source contributions to deposition zones and the sediment transport distances, corroborate the morphological observations and demonstrate the potential of using REE for quantifying sediment transport processes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Based on hypotheses derived directly from experimental observations of the triaxial behaviour, a constitutive model for fibre reinforced sands is built in this paper. Both the sand matrix and the fibres obey their own constitutive law, whereas their contributions are superimposed using a volumetric homogenization procedure. The Severn‐Trent sand model, which combines well‐known concepts such as critical state theory, Mohr‐Coulomb like strength criterion, bounding surface plasticity and kinematic hardening, is adopted for the sand matrix. Although the fibres are treated as discrete forces with defined orientation, an equivalent continuum stress for the fibre phase is derived to allow the superposition of effects of sand and fibres. The fibres are considered as purely tensile elements following a linear elastic constitutive rule. The strain in the fibres is expressed as a fraction of the strain in the reinforced sample so that imperfect bonding is assumed at the sand‐fibre interface. Only those fibres oriented within the tensile strain domain of the sample can mobilize tensile stress—the orientation of fibres is one of the key ingredients to capture the anisotropic behaviour of fibre reinforced soil that is observed for triaxial compression and extension loading. A further mechanism of partition of the volume of voids between the fibres and the sand matrix is introduced and shown to be fundamental for the simulation of the volumetric behaviour of fibre‐reinforced soils. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Landslide stability analysis increasingly utilises high-resolution coupled hydrology–slope stability models (CHASM) to improve stability assessments in areas subject to dynamic pore pressure regimes. In such environments, the estimation of soil hydraulic conductivity (K) is a key parameter but one which is not always readily available or determined with the required resolution. By using basic soil particle-size distribution (PSD) data, we evaluate the microscopic composition of the actual soil, and applying the analytical relations obtain by a Self-Consistent Method (SCM) approach, we determine an appropriate value of K. This is of importance in that it allows within-soil type variability to be reflected in terms of K and hence within the model structure. The SCM methodology is briefly reviewed and an illustrative application is undertaken for a slope typical of Hong Kong. The results show model output sensitivity in terms of moisture content and factor of safety (FOS) when comparing K values determined using the SCM approach and the conventional field determination. In attempting to determine slope hydrological processes and attendant stability conditions, we conclude that the application of SCM approach offers a novel methodology for potentially improving the parameterisation of hydrology–slope stability models. 相似文献
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Erdin Ibraim Herve Di Benedetto Thiep Doanh 《Geotechnical and Geological Engineering》2009,27(1):181-191
Recent laboratory and field experiments have confirmed that sand does indeed exhibit time-dependent behaviour. Based on these
findings, it was considered necessary to revisit some of the published experimental results on the static liquefaction phenomenon
of loose anisotropic Hostun RF sand. Time-dependency might have had a significant influence on the observed undrained response
of anisotropic consolidated sand specimens. Specific triaxial tests have been performed and a qualitative analysis is presented
in this paper. It is shown that, despite the differences on the anisotropic consolidation path employed, different specimens
show qualitatively identical undrained responses if creep periods are performed at identical test stages or if the anisotropic
consolidation takes place very slowly. With time, the undrained stiffness and strength are considerably improved and this
may explain why the static liquefaction phenomenon is not as common in practice as could be predicted based on an instability
line concept. Whereas the original instability line concept was developed independently of time-dependency, in field situations,
the liquefaction resistance of the sand can increase with time. 相似文献
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AbstractThe aim of this study was to understand seasonal variations in the vertical structure of the water column, and to quantify the importance of the physical forces (solar radiation, wind and hydraulic retention time) that control mixing processes in a reservoir bordering the Pantanal floodplain. Samples were taken every three months in the reservoir centre, at four depths, for the measurement of nine physical and chemical water quality parameters. The reservoir presented a long stratification period with complete mixing in winter. The vertical structure showed that, during the stratification period, the upper layers of the reservoir are homogeneous and the physical and chemical composition only changes at greater depths. The wind acting over an extended period is the only factor that significantly influences the vertical structure in the reservoir, giving rise to mixing processes. Moreover, the position of the draw-off point in the upper layer of the reservoir, together with the reservoir depth, enhances vertical stability. 相似文献
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In situ experiments and seismic analysis of existing buildings. Part II: Seismic integrity threshold
The interest of in situ measurements (presented in Part I paper) for a seismic assessment of existing buildings is analysed in this paper. It is shown that the experimental modal characteristics obtained on regular concrete structures are described successfully by suited Timoshenko beam modelling. For a given structure, taking into account the experimental data, the corresponding beam model, and choosing the maximum tensile strain of concrete as damage criterion for key structural elements, a maximum level of the ground acceleration can be determined. This so‐called seismic integrity threshold is directly related to the onset of structural damages. This new approach is illustrated on one of the studied buildings. The advantages of using ambient vibrations survey for the vulnerability assessment of existing buildings are discussed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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A new constitutive model for fibre-reinforced cohesive soil is proposed. The model combines a Cam-Clay like bounding surface model with an elastic–plastic one-dimensional fibrous element model. A “smearing procedure”, which can consider any spatial distribution of fibre orientation, is employed to transform discrete tensile forces developed in the fibres into stresses for the composite material. The fibre stress contribution is bounded by both degradation of soil–fibre bonding due to pull-out mechanism and tensile strength of the fibres. Eventual occurrence of fibre breakage is also considered. The model performances are analysed for both consolidation and shearing loading modes, and qualitative comparison is performed with experimental data available in the literature. For consolidation loading, tensile stresses are not developed in the fibres and thus the fibre effect is rather limited. For drained shear loading, addition of fibres can result in a consistent shear strength increase. The beneficial effect of fibres seems to be controlled by two parameters: the fibre tensile stiffness and the fibre/soil strain ratio that accounts for any possible slippage or shear deformation at the fibre/soil matrix interface. For undrained shear loading, the strengthening effect of the fibres appears to be counteracted by the increase in pore water pressure, induced by the additional confining contribution of the fibres. In agreement with published experimental data, the model suggests also that the moisture content is a key factor governing fibre effectiveness for undrained shearing. Finally, analysis of the model predicted critical states for fibre-reinforced cohesive soil is provided. 相似文献
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Hoch Bruna Zakharia Diambra Andrea Ibraim Erdin Festugato Lucas Consoli Nilo Cesar 《Acta Geotechnica》2022,17(7):2955-2969
Chalk breaks easily when subjected to human action such as mechanical handling, earthworks operations or pile installation. These actions break the cemented structure of chalk, which turns into a degraded material known as putty, with lower strength and stiffness than the intact chalk. The addition of Portland cement can improve the behaviour of chalk putties. Yet, there are no studies determining the tensile strength of chalk putty–cement blends, the initial stiffness evolution during the curing time and other design parameters such as friction angle and cohesion of this material. This paper addresses this knowledge gap and provides an interpretation of new experimental results based on the dimensionless index expressed as the ratio between porosity and volumetric content of cement (η/Civ) or its exponential modification (η/Civa). This index aids the selection of the amount of cement and density for key design parameters of compacted chalk putty–cement blends required in geotechnical engineering projects such as road foundations and pavements, embankments, and also bored concrete pile foundations.
相似文献9.
Recent results of in situ measurements and their interest for a seismic assessment of existing buildings are presented and analysed. The present paper (Part I) is devoted to the experimental programme. The response to ambient vibrations, harmonic excitation and shock loading is recorded on intact buildings but also after their structure or their vicinity was modified. These tests aim to identify the dynamic behaviour of ordinary intact buildings built in a conventional practise. Moreover, taking advantage of their demolition, it was possible (through these tests) to determine the actual influence of the light work elements, full precast facade panels, bearing masonry walls, and the presence of neighbouring joined buildings. These experiments realized on real buildings show that information gathered from ambient measurements provide reliable and efficient data of real interest for a clear understanding of the actual building behaviour. The advantage of integrating these data in the vulnerability assessment is presented and discussed in the next paper (Part II). Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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