A model for grain-size sorting over tidal sand ridges     

M. Walgreen  H.E. de Swart  D. Calvete 《Ocean Dynamics》2004,54(3-4):374-384

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  相似文献   

Monitoring and modelling of pore water pressure changes and riverbank stability during flow events   总被引：1，自引：0，他引：1  

Massimo Rinaldi  Nicola Casagli  Stefano Dapporto  Alessandro Gargini 《地球表面变化过程与地形》2004,29(2):237-254

Pore water pressures (positive and negative) were monitored for four years (1996–1999) using a series of tensiometer‐piezometers at increasing depths in a riverbank of the Sieve River, Tuscany (central Italy), with the overall objective of investigating pore pressure changes in response to ?ow events and their effects on bank stability. The saturated/unsaturated ?ow was modelled using a ?nite element seepage analysis, for the main ?ow events occurring during the four‐year monitoring period. Modelling results were validated by comparing measured with computed pore water pressure values for a series of representative events. Riverbank stability analysis was conducted by applying the limit equilibrium method (Morgenstern‐Price), using pore water pressure distributions obtained by the seepage analysis. The simulation of the 14 December 1996 event, during which a bank failure occurred, is reported in detail to illustrate the relations between the water table and river stage during the various phases of the hydrograph and their effects on bank stability. The simulation, according to monitored data, shows that the failure occurred three hours after the peak stage, during the inversion of ?ow (from the bank towards the river). A relatively limited development of positive pore pressures, reducing the effective stress and annulling the shear strength term due to the matric suction, and the sudden loss of the con?ning pressure of the river during the initial drawdown were responsible for triggering the mass failure. Results deriving from the seepage and stability analysis of nine selected ?ow events were then used to investigate the role of the ?ow event characteristics (in terms of peak stages and hydrograph characteristics) and of changes in bank geometry. Besides the peak river stage, which mainly controls the occurrence of conditions of instability, an important role is played by the hydrograph characteristics, in particular by the presence of one or more minor peaks in the river stage preceding the main one. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Fundamental study on the response characteristics of drivers during an earthquake based on driving simulator experiments     

Yoshihisa Maruyama  Fumio Yamazaki 《地震工程与结构动力学》2004,33(6):775-792

After the 1995 Kobe earthquake, the expressway structures in Japan were retrofitted and they will not now be seriously damaged under a certain level of strong earthquake motion. However, the stability of a moving vehicle has not been investigated yet. It has been reported that drivers feel seismically induced vibrations, especially in the transverse direction of vehicles. Owing to this phenomenon, drivers have some difficulty in controlling the vehicles during strong shaking. For further safety promotion of the expressway networks, it is important to understand the drivers' reactions to seismic motion. The present authors have performed a series of seismic response analyses of a moving vehicle to investigate its response characteristics based on numerical simulation. However, the responses of the driver were not considered in the simulation process. In order to investigate the drivers' reactions during an earthquake, a series of virtual tests were conducted using a driving simulator. This driving simulator has six servomotor‐powered electric actuators that control its motions. Several types of tests were carried out for different examinees to investigate drivers' responses while controlling the simulator under seismic motion. The results of this study showed that a larger response time lag to strong shaking and over turning of the steering wheel may shift the vehicle into the next lane. According to this finding, trafficaccidents could possibly occur under strong ground shaking in the case of heavy traffic. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

变形监测基准点的稳定性检验   总被引：1，自引：0，他引：1  

詹龙喜  唐继民  汪维春  周金龙 《上海国土资源》2004,(2):34-36,43

基准点的稳定性评价，是变形观测数据处理时不可忽视的重要内容。该文对基准点构网和不构网2种情况时的数据处理方法进行了探讨。  相似文献   

昌马水库右岸山体稳定性研究   总被引：2，自引：0，他引：2  

杨健  陈祖煜  何传永 《水文地质工程地质》2004,31(1):24-27

昌马水库导流排砂洞塌方导致右岸山体发生松动 ,本文在大量地质资料的基础上 ,对右岸岩体裂隙网络进行模拟 ,同时 ,采用极限分析能量法和有限元数值模拟方法等对右岸山体的稳定性进行分析研究 ,并提出相应的加固方案。  相似文献   

吉林台水电站厂房高边坡稳定性及加固措施研究   总被引：2，自引：0，他引：2  

杨健  耿克勤 《水文地质工程地质》2004,31(2):41-44

吉林台水电站厂房后边坡开挖形成140～340m的高边坡,保证其长期运行稳定性至关重要。在结合地质资料对边坡的失稳模式进行初步判断的基础上,采用极限平衡分析方法对正常蓄水、暴雨影响、地震荷载等工况条件下边坡的整体抗滑稳定性进行分析,得出暴雨对边坡稳定影响较大的结论,据此提出以排水结合预应力锚索为主的边坡加固增稳措施,实践证明该措施是有效的。  相似文献   

活树桩固坡对边坡稳定性影响的数值分析   总被引：13，自引：0，他引：13  

徐中华  钭逢光  陈锦剑  王建华  封金财 《岩土力学》2004,25(Z2):275-279

作为一种经济、环保的植物固坡方法,活树桩在发达国家得到了较为广泛的应用.笔者介绍了活树桩固坡方法的应用和施工方法,讨论了其加固机理.采用弹塑性有限元分析活树桩固坡对边坡稳定性的影响,研究了活树桩的入土长度、加固位置、数量、角度及其根系发展等因素对边坡安全系数影响的规律.  相似文献   

大渡河次级支流斯合沟泥石流特征研究   总被引：1，自引：1，他引：1  

王小群  王兰生  李天斌  赵其华 《中国地质灾害与防治学报》2004,15(1):28-32

泥石流作为地质环境较差、的山区的主要自然灾害之一，对它的研究尤其是泥石流规律方面的研究已取得了较大的成绩。但是对于泥石流的研究思路却有待进一步发展和完善，这在很大程度上将对山区的工程建设有很重要的指导意义。论文从工程地质研究思路的角度出发，对位于大渡河支流官料河上某水电站下闸址区的斯合沟泥石流进行了研究。文中采用工程地质分析的方法对大渡河次级支流斯台沟泥石流的形成环境(地层岩性条件、构造条件、地貌条件、气象条件、植被发育及人类活动)、基本特征(泥石流沟的基本特征、泥石流的堆积特征)进行了系统的研究，提出了该泥石流的形成演化过程及其机制模型(初期是堰塞式沟谷型泥石流，后期逐渐转向汇聚式沟谷型泥石流)。并在此基础上对泥石流沟沿岸的岸坡稳定性(可能泥石流的物源)等进行了评价分析。将定性分析和定量分析相结合，对泥石流的活动趋势以及可能泥石流的体积(未来泥石流形成将主要是在面蚀和沟蚀作用下的坡面泥石流。泥石流规模较小，且由于沟谷中下游坡降的进一步减缓，形成的泥石流物质一般将沿途停积．实际进入官料河内的体积很小)做出了较为科学的评价预测。经过这样的系统分析对工程建设中的泥石流防治有着积极的指导意义。  相似文献   

某浅埋地下洞室围岩稳定及渐进破坏过程分析     

潘永坚  陈光 《水文地质工程地质》2004,31(3):69-71

以新疆乌鲁木齐市"世纪花苑"三期工程废弃人防地道为实例,在查明研究区浅埋洞室分布特征的基础上,结合现场及室内试验获取相关岩土体物理力学参数,利用快速拉格朗日差分分析程序FLAC研究浅埋洞室在拟建高层荷载作用下的稳定性及其破坏过程,通过系列模拟图,较真实地再现了洞室围岩变形破坏、尤其是塑性区发展变化过程。  相似文献   

昆明白泥井3号隧道围岩稳定性FLAC3D模拟   总被引：4，自引：2，他引：4  

吴传斌  施斌  孙宇  赵永贵 《水文地质工程地质》2004,31(6):52-55

应用FLAC^3D数值模拟软件对昆明白泥井3号隧道围岩稳定性进行了分析和评价。结果表明隧道支护后围岩的最大变形出现在隧道右侧拱顶，为1．00cm；隧道支护后左侧拱和右侧拱脚处剪应变明显增大，为应力集中区；围岩可以通过自身应力、应变和能量的调整，使整个隧道围岩处于稳定状态；同时也表明FLAC^3D用于隧道围岩变形分析是可行的。  相似文献