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91.
G. Lefeuve-Mesgouez A. T. Peplow D. Le Houdec 《Soil Dynamics and Earthquake Engineering》2002,22(6):692
The transmission of vibrations over the surface of the ground, due to high-speed moving, vertical harmonic rectangular loads, is investigated theoretically. The problem is three-dimensional and the interior of the ground is modelled as an elastic half-space or a multilayered ground. The transformed solutions are obtained using the Fourier transform on the space variable. A new damping model in the spatial wavenumber domain, presented in Lefeuve-Mesgouez et al. [J. Sound. Vibr. 231 (2000) 1289] is used. Numerical results for the displacements on the surface are presented for loads moving with speeds up to and beyond the Rayleigh wave speed of the half-space. 相似文献
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The three-dimensional flow field in a scour hole around different abutments under a clear water regime was experimentally measured in a laboratory flume, using the Acoustic Doppler Velocimeter (ADV). Three types of abutments used in the experiments were vertical-wall (rectangular section), 45° wing-wall (45° polygonal section) and semicircular. The three-dimensional time-averaged velocity components were detected at different vertical planes for vertical-wall abutment and azimuthal planes for wing-wall and semicircular abutments. The velocity components were also measured at different horizontal planes. In the upstream, presentations of flow field through vector plots at vertical / azimuthal and horizontal planes show the existence of a primary vortex associated with the downflow inside the scour hole. On the other hand, in the downstream, the flow field shows a reversed flow near the abutments having a subsequent recovery with a passage of flow as a part of the main flow. The data presented in this p 相似文献
95.
A recently exposed section across a ?rst‐order valley buried beneath the regional blanket peat on hillside slopes in the upper Liffey valley, Co. Wicklow, is described. The section shows two alluvia within a shallow valley form underlain by an extensive boulder and stone line over regional till and weathered granite. 14C dates from wood in the alluvia indicate the older alluvium to have formed between 4324 ± 53 BP and 4126 ± 45 BP and the younger between 3217 ± 53 BP and 2975 ± 53 BP . The basal layer of the overlying peat yielded a date of 2208 ± 61 BP . The younger alluvium shows the effects of soil paludi?cation prior to the peat expansion. Dated pollen analyses elsewhere in the upper catchment con?rm the spread of blanket peat over most areas above 350 m after 4000–3600 BP . The buried valley was contributing sediments to the mid‐Holocene ?oodplains in the upper Liffey valley prior to the extension of blanket peat over the catchment after which sediment yields from it and the other catchment slopes declined. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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Stanley W. Trimble 《Environmental Geology》1997,32(3):230-234
A significant proportion of stream sediment yield in North America comes from stream channel and bank erosion. One method
used for stream stabilization is the bank installation of timber and stone fish-shelter structures, but there is little evidence
for their potential effectiveness. Nine to nineteen years of precise survey data from Coon Creek, Wisconsin, however, show
that fish structures enhance sediment deposition along the stream and may retard lateral migration of channels. Such structures
have greater utility for sediment control when streams are eroding away a high bank and replacing it with a lower bank.
Received: 18 October 1996 · Accepted: 4 February 1997 相似文献
99.
河北平原南部曲周地区一河间洼地剖面中240cm,160cm和80cm深度处的AMS14C测年结果分别为10210±80aB.P.,8270±70aB.P.和6500±60aB.P.。由这3个测年数据和代用指标数据相结合推测的曲周地区全新世古环境状况及其变化与其他研究者在其他地区,尤为河北平原其他地区所获的结果是相同或相似的,并且在时间上是吻合的。由这3个数据推导的沉积物的埋深、厚度、堆积速率以及岩性等特征大都是这一剖面所处沉积环境和构造活动部位的反映,与前人有关河间洼地沉积的基本特征及其影响因素的阐述是相符的。充分认识河间洼地沉积物的特征,尤为其与河道沉积等的差别,对于更全面、深入地了解河流系统可能是有益的 相似文献
100.
Field vibration mitigation by honeycomb WIB for pile foundations of a high-speed train viaduct 总被引:5,自引:0,他引:5
Environmental vibrations from recent high-speed trains are becoming a special concern in the civil and environmental engineering field since they can give detrimental effects to residents, sensitive equipments and high-tech production facilities in the vicinity of train tacks. Herein, aiming at the vibration mitigation for a specific high-tech industrial area, the low-frequency vibrations from a train viaduct are targeted over an anticipated range. A theoretically designed innovative countermeasure, called honeycomb wave impeding barrier (WIB) for a wave impeding barrier, is introduced and its effects are investigated by computer simulation. The present WIB is based on the wave dispersion phenomenon that can modulate the incoming wavelengths into the shorter wavelengths, creating an apparent wave cut-off characteristic in the wave field across WIB installation area. The shorter wavelengths are further impeded due to the impedance ratio of the WIB walls and in-fill materials and absorbed by the in-fills more. The three-dimensional FEM simulation demonstrates a dramatic reduction effect that is difficult to achieve by conventional measures. 相似文献