Study of the liquefaction resistance of a saturated sand reinforced with Geosynthetics

This article presents various tests using a cyclic triaxial instrument, on samples of saturated Hostun RF sand, reinforced with circular sheets of geosynthetic material. Tests performed with different types of geosynthetics of different compressibility, rigidity and roughness characteristics indicate a significant increase in liquefaction resistance for samples reinforced with compressible, non-woven geotextiles. The undrained behaviour of saturated Hostun RF sand reinforced with non-woven geotextiles is analysed on the basis of different test series. This analysis highlights the influence of reinforcement compressibility on interstitial pressure distribution in the sample, thus showing the role of this type of inclusion in the increase in liquefaction resistance.     

珊瑚礁工程地质研究的内容和方法

珊瑚礁工程地质研究的主要内容为珊瑚礁自然地质条件、珊瑚礁岩土物理力学性质和珊瑚礁混凝土料问题。除了通常的工程地质研究方法外, 着重介绍珊瑚礁工程地质研究的钻探、触探和地球物理勘测方法。     

国内外PMP/PMF的发展和实践

对20世纪80年代以来PMP／PMF在国内外的发展和实践情况作了简要的介绍和评论。内容包括PMP／PMF定义、估算方法、成果合理性检查和概率。PMP估算方法包括概化估算法、当地暴雨放大、暴雨移置、暴雨组合、推理模式和统计估算法。PMF估算着重介绍了由PMP转化为PMF的产流和汇流特点，以及目前在南非和法语非洲国家广泛应用的经验公式。     

榆林风沙滩区水资源可持续利用对策与建议

本文在对榆林风沙滩区内水资源条件、开发利用现状及存在问题等调查研究资料进行深入分析的基础上,结合国民经济各业未来发展对水资源的需求情况,确定了未来不同水平年的需水量和供水量,并通过供需平衡分析,提出了解决水资源短缺的途径和实现水资源合理开发利用的建议.     

A model for grain-size sorting over tidal sand ridges

A model was developed and analyzed to quantify the effect of graded sediment on the formation of tidal sand ridges. Field data reveal coarse (fine) sediment at the crests (in the troughs), but often phase shifts between the mean grain-size distribution and the bottom topography occur. Following earlier work, this study is based on a linear stability analysis of a basic state with respect to small bottom perturbations. The basic state describes an alongshore tidal current on a coastal shelf. Sediment is transported as bed load and dynamic hiding effects are accounted for. A one-layer model for the bed evolution is used and two grain size classes (fine and coarse sand) are considered. Results indicate an increase in growth and migration rates of tidal sand ridges for a bimodal mixture, whilst the wavelength of the ridges remains unchanged. A symmetrical externally forced tidal current results in a grain-size distribution which is in phase with the ridges. Incorporation of an additional external M₄ tidal constituent or a steady current results in a phase shift between the grain-size distribution and ridge topography. These results show a general agreement with observations. The physical mechanism responsible for the observed grain-size distribution over the ridges is also discussed.Responsible Editor: Jens Kappenberg     

Comparison of hydraulic geometry between sand‐ and gravel‐bed rivers in relation to channel pattern discrimination

A comparison has been made between the hydraulic geometry of sand‐ and gravel‐bed rivers, based on data from alluvial rivers around the world. The results indicate a signi?cant difference in hydraulic geometry among sand‐ and gravel‐bed rivers with different channel patterns. On this basis, some diagrams for discrimination of meandering and braided channel patterns have been established. The relationships between channel width and water discharge, between channel depth and water discharge, between width–depth ratio and water discharge and between channel slope and water discharge can all be used for channel pattern discrimination. The relationship between channel width and channel depth can also be used for channel pattern discrimination. However, the accuracy of these relationships for channel pattern discrimination varies, and the depth–discharge relationship is a better discriminator of pattern type than the classic slope–discharge function. The cause for this difference has been explained qualitatively. To predict the development of channel patterns under different natural conditions, the pattern discriminator should be searched on the basis of independent or at least semi‐independent variables. The relationship between stream power and bed material grain size can be used to discriminate channel patterns, which shows a better result than the discriminator using the slope–discharge relationship. Copyright © 2004 John Wiley & Sons, Ltd.     

Modelling transverse dunes

Transverse dunes appear in regions of mainly unidirectional wind and high sand availability. A dune model is extended to two‐dimensional calculation of the shear stress. It is applied to simulate dynamics and morphology of three‐dimensional transverse dunes. In the simulations they seem to reach translational invariance and do not stop growing. Hence, simulations of two‐dimensional dune ?elds have been performed. Characteristic laws were found for the time evolution of transverse dunes. Bagnold's law of the dune velocity is modi?ed and reproduced. The interaction between transverse dunes led to the interesting conclusion that small dunes can travel over bigger ones. Copyright © 2004 John Wiley & Sons, Ltd.     

一次强风暴的垂直环境特征数值模拟分析

应用MM 5模式对东北冷涡诱发的 2 0 0 2年 7月 1 2日强风暴进行了数值模拟 ,较成功地模拟出中尺度强对流风暴。发现冷涡后部中层干冷空气绝热下沉是东北冷涡 70 0hPa附近干暖盖形成和维持的重要机制 ,而低层暖湿气流爬升及干暖盖的抑制作用是东北冷涡强对流不稳定能量积累的重要机制。风暴发生前持续的低层西南风到中层西北风的风垂直切变产生的差动平流 ,加剧了层结不稳定 ,而风暴临近风垂直切变方向的快速逆转使热成风不平衡 ,必须通过激发垂直环流以适应其变化 ,对风暴发展有重要作用。     

沈阳地区沙尘天气分析

本文总结了沈阳地区沙尘天气的时空分布特点，从天气条件、地表自然条件(沙源)两方面分析了沈阳地区沙尘天气的成因，总结了沈阳地区预报沙尘天气时应参考的5个因素。     

牡丹江市大--暴雨中期预报方法研究

应用MICAPS平台所提供的数值预报产品，分析影响牡丹江市大一暴雨的天气系统，并找出关键区域及预报指标，在实际预报中取得了很好的效果。