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101.
Topographic interactions generate multidirectional and unsteady air?ow that limits the application of velocity pro?le approaches for estimating sediment transport over dunes. Results are presented from a series of wind tunnel simulations using Irwin‐type surface‐mounted pressure sensors to measure shear stress variability directly at the surface over both isolated and closely spaced sharp‐crested model dunes. Findings complement existing theories on secondary air?ow effects on stoss transport dynamics and provide new information on the in?uence of lee‐side air?ow patterns on dune morphodynamics. For all speeds investigated, turbulent unsteadiness at the dune toe indicates a greater, more variable surface shear, despite a signi?cant drop in time‐averaged measurements of streamwise shear stress at this location. This effect is believed suf?cient to inhibit sediment deposition at the toe and may be responsible for documented intermittency in sand transport in the toe region. On the stoss slope, streamline compression and ?ow acceleration cause an increase in ?ow steadiness and shear stress to a maximum at the crest that is double that at the toe of the isolated dune and 60–70 per cent greater than at ?ow reattachment on the lower stoss of closely spaced dunes. Streamwise ?ow accelerations, rather than turbulence, have greater in?uence on stress generation on the stoss and this effect increases with stoss slope distance and with incident wind speed. Reversed ?ow within the separation cell generates signi?cant surface shear (30–40 per cent of maximum values) for both spacings. This supports ?eld studies that suggest reversed ?ow is competent enough to return sediment to the dune directly or in a de?ected direction. High variability in shear at reattachment indicates impact of a turbulent shear layer that, despite low values of time‐averaged streamwise stress in this region, would inhibit sediment accumulation. Downwind of reattachment, shear stress and ?ow steadiness increase within 6 h (h = dune height) of reattachment and approach upwind values by 25 h. A distance of at least 30 h is suggested for full boundary layer recovery, which is comparable to ?uvial estimates. The Irwin sensor used in this study provides a reliable means to measure skin friction force responsible for sand transport and its robust, simple, and cost‐effective design shows promise for validating these ?ndings in natural dune settings. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
102.
三峡库区云阳新城水平层状岩体高边坡变形破坏主要控制因素 总被引:3,自引:0,他引:3
本文对三峡库区云阳新城一些高边坡的勘察成果进行了总结,目的在于了解云阳新城区近水平岩层条件下边坡变形破坏的型式、主要控制因素及支护要点。结果表明,云阳新城高边坡普遍存在表层剥落现象,含膨胀性矿物(主要是伊利石和绿泥石)的泥质岩较快速风化作用是造成边坡表层剥落式渐进性破坏的主要原因;沿卸荷裂隙与泥化夹层的崩滑是边坡失稳的主要型式,但边坡之间崩滑失稳的程度存在较大差异,一些边坡存在相对较为强烈的卸荷及边坡失稳问题,主要归因于其存在与边坡近于平行的构造裂隙。认为及时进行护坡并在工程设计中考虑结构面的存在型式是边坡防护的重点。 相似文献
103.
The effects of uncertainty due to the variability of soil parameters on the risk of landsliding in the Himalayan region are investigated using a random field model combined with slope stability analyses. Effects of spatial variability both in horizontal and vertical directions, number of test samples, variations in piezometric level and the influence of earthquake on the reliability of a typical slope in a slide area are investigated. The results show that the reliability of slopes in the slide area is significantly affected by the coefficients of variation of soil parameters, spatial variations of soil parameters, number of test samples and piezometric variations. The results also show that the assumption of isotropic variations to assess slope reliability isconservative. The results of the study are useful in providing guidelines and pointing to remedial measures in the form of sub-surface drainage to improve slope reliability in the area. 相似文献
104.
105.
洪家渡水电站左坝肩高边坡稳定及加固措施研究 总被引:1,自引:0,他引:1
贵州洪家渡水电站左坝肩高边坡开挖高度310 m,采用弹塑性有限元数值模拟方法对左坝肩高边坡施工期岩体应力应变状态进行分析研究,并结合现场变形观测资料对计算结果进行验证,从而对左坝肩高边坡的稳定性进行评价并提出相应的加固措施。 相似文献
106.
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109.
边坡及其它类工程地质问题研究 总被引:2,自引:0,他引:2
徐嘉谟 《水文地质工程地质》1997,24(2):35-38
本文提出有关边坡工程地质研究方面的一些新概念,看法和问题,并概述了属地这一专题的边坡及其它各类工程地质问题的研究成果。 相似文献
110.
斜坡岩体由小变形到大变形乃至滑坡的发生,实质上是由组成斜坡的各子系统协同作用的结果.将协同学引入斜坡的稳定性预测评价中,并提出了一种新的斜坡失稳时间预测模型──协同预测模型.经实例检验,该模型预测精度较高,可用于滑坡的短期或临滑预报. 相似文献