Simulation and measurement of surface shear stress over isolated and closely spaced transverse dunes in a wind tunnel     

Ian J. Walker  William G. Nickling 《地球表面变化过程与地形》2003,28(10):1111-1124

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   

Jurassic Dextral and Cretaceous Sinistral Movements Along the Hida Marginal Belt     

Kazuhiro Tsukada 《Gondwana Research》2003,6(4):687-698

The Hida marginal belt (HMB), which consists of various kinds of fault-bound blocks, is located between the continental massif of the Hida belt and the Mesozoic accretionary complex of the Mino belt in Central Japan. Detailed field investigation reveals that the HMB had grown through the two different movements, i.e., Jurassic dextral and Cretaceous sinistral movements. The Jurassic dextral ductile shear zones run in the southern marginal part of the Hida belt and the northern part of the HMB, whereas the Cretaceous sinistral cataclastic shear zones occur in the southern part of the HMB and the northern marginal part of the Mino belt. Geologic map and field evidence seem to suggest that the Jurassic dextral movement form the fault-bound blocks of the HMB to form the basic structure of the Hida marginal belt, i.e., formation of the ‘proto-HMB.’ Following the dextral movement, the sinistral one restructured the ‘proto-HMB’ to complete the present feature of the Hida marginal belt. The Cretaceous sinistral movement might result in the sinistral collision between the proto-HMB and the Mino belt.  相似文献   

Seismic wave velocity and anisotropy of serpentinized peridotite in the Oman ophiolite     

Benoît Dewandel  Franoise Boudier  Hartmut Kern  Waris Warsi  David Mainprice 《Tectonophysics》2003,370(1-4):77-94

Shallow seismic measurements in harzburgite from the Oman ophiolite performed in a zone where the maximum horizontal anisotropy is expected (vertical foliation and horizontal lineation) point to a dominant dependence of seismic properties on fracturing.

Optical microscopy studies show that microcracks are guided by the serpentine (lizardite) penetrative network oriented subparallel to the harzburgite foliation and subperpendicular to the mineral lineation, and that serpentine (lizardite) vein filling has a maximum concentration of (001) planes parallel to the veins walls. The calculated elastic properties of the oriented alteration veins filled with serpentine in an anisotropic matrix formed by oriented crystals of olivine and orthopyroxene are compared with seismic velocities measured on hand specimens.

Laboratory ultrasonic data indicate that open microcracks are closed at 100 MPa pressure, e.g. (J. Geophys. Res. 65, (1960) 1083) and (Proc. ODP Sci. Results Leg 118, (1990) 227). Above this pressure, laboratory measurements and modeling show that P-compressional and S-shear wave velocities are mainly controlled by the mineral preferred orientation. Veins sealed with serpentine are effective in slightly lowering P and S velocities and increasing anisotropy. The penetrative lizardite network does not affect directly the geometry of seismic anisotropy, but contributes indirectly in the fact that this network controls the microcrack orientations.

Comparison between seismic measurements of peridotite and gabbro in the same conditions suggest that P- and S-waves anisotropies are a possible discriminating factor between the two lithologies in the suboceanic lithosphere.  相似文献   

Contrasting metamorphic evolution of metasedimentary rocks from the Çine and Selimiye nappes in the Anatolide belt, western Turkey   总被引：1，自引：0，他引：1  

J. L. Régnier  U. Ring  C. W. Passchier  K. Gessner  T. Güngör 《Journal of Metamorphic Geology》2003,21(7):699-721

Abstract P–T conditions, mineral isograds, the relation of the latter to foliation planes and kinematic indicators are used to elucidate the tectonic nature and evolution of a shear zone in an orogen exhumed from mid‐crustal depths in western Turkey. Furthermore, we discuss whether simple monometamorphic fabrics of rock units from different nappes result from one single orogeny or are related to different orogenies. Metasedimentary rocks from the Çine and Selimiye nappes at the southern rim of the Anatolide belt of western Turkey record different metamorphic evolutions. The Eocene Selimiye shear zone separates both nappes. Metasedimentary rocks from the Çine nappe underneath the Selimiye shear zone record maximum P–T conditions of about 7 kbar and >550 °C. Metasedimentary rocks from the overlying Selimiye nappe have maximum P–T conditions of 4 kbar and c. 525 °C near the base of the nappe. Kinematic indicators in both nappes are related to movement on the Selimiye shear zone and consistently show a top‐S shear sense. Metamorphic grade in the Selimiye nappe decreases structurally upwards as indicated by mineral isograds defining the garnet‐chlorite zone at the base, the chloritoid‐biotite zone and the biotite‐chlorite zone at the top of the nappe. The mineral isograds in the Selimiye nappe run parallel to the regional S_R foliation, parallel the Selimiye shear zone and indicate that the Selimiye shear zone formed during this prograde greenschist to lower amphibolite facies metamorphic event but remained active after the peak of metamorphism. ⁴⁰Ar/³⁹Ar mica ages and the tectonometamorphic relationship with the Eocene Cyclades–Menderes thrust, which occurs above the Selimiye nappe in the study area, suggests an Eocene age of metamorphism in the Selimiye nappe. Metasedimentary rocks of the Çine nappe 20–30 km north of the Selimiye shear zone record maximum P–T conditions of 8–11 kbar and 600–650 °C. An age of about 550 Ma is indicated for amphibolite facies metamorphism and associated top‐N shear in the orthogneiss of the Çine nappe. Our study shows that simple monophase tectonometamorphic fabrics do not always indicate a simple orogenic development of a nappe stack. Preservation in some areas and complete overprinting of those fabrics in other areas apparently occur very heterogeneously.  相似文献   

新疆某水利枢纽工程软弱结构面抗剪强度参数的试验研究     

袁天华  席福来  努尔哈斯木 《岩土力学》2003,(Z1)

某水利枢纽工程位于伊犁地区,影响工程的主要问题为坝基岩体软弱结构面和断层的抗滑稳定问题。根据工程实际条件和软弱夹层特性,采取现场断层软弱结构面试验和室内模拟试验相结合,获得软弱夹层的抗剪参数。实践证明,把两种方法结合起来的试验成果可靠,尤其对一些不具备进行现场大型岩体软弱夹层抗剪试验的工程,采用室内中型直剪仪进 行剪切试验具有实用意义。  相似文献   

基于统一强度理论的柱形孔扩张问题研究   总被引：5，自引：1，他引：5  

王延斌  范文  徐栓强 《岩土力学》2003,(Z2)

考虑了岩土材料的软化和剪胀特性,利用空间轴对称问题的统一强度理论分析了柱形孔扩张问题,求出了岩土材料在柱形孔扩张时的应力场、应变场、位移场和最终扩张压力的统一解表达式。对蒋明镜-沈珠江扩孔公式从不同的方面作了论述。通过算例分析了岩土材料的软化和剪胀特性以及统一强度理论参数对应力场、位移场和扩张压力的影响。已有的关于该问题的Tresca解和Mohr-Coulomb解均为本文的一个特例。  相似文献   

重塑非饱和粘土抗剪强度参数与饱和度的关系研究   总被引：3，自引：0，他引：3  

熊承仁  刘宝琛  张家生  刘多文 《岩土力学》2003,(Z2)

土的饱和度是基于水分状态和密度状态的一个衍生变量。存在因应水分状态变化和因应密度状态变化的两类饱和度变化过程。根据23组不同水分状态和密度状态的UU三轴压缩试验结果,讨论了重塑非饱和粘性土抗剪强度参数与饱和度的关系。数据分析表明:粘聚力与水分状态相关的饱和度的关系是强非线性的,与密度状态相关的饱和度的关系是准线性的。内摩擦角与水分状态相关的饱和度的关系是强非线性的,与密度状态相关的饱和度的关系是弱非线性的。  相似文献   

岩质边坡稳定性分析的探讨   总被引：2，自引：0，他引：2  

张飞  池秀文 《岩土力学》2003,(Z2)

通过最大剪应力等值线来确定边坡的滑动面,并与其结构面抗剪强度相比较,给出了确定边坡的稳定系数的方法。  相似文献   

非饱和土抗剪强度理论的研究进展   总被引：6，自引：0，他引：6  

陈敬虞  Fredlund D.G. 《岩土力学》2003,(Z2)

非饱和土的工程性质是20世纪90年代以来国际岩土工程界研究的热点,非饱和土的抗剪强度是非饱和土的重要工程性质之一,在参阅了中、外文相关资料的基础上,总结了非饱和土抗剪强度理论的研究成果,提出了非饱和土抗剪强度有待进一步研究的问题。  相似文献   

Use of accessory zircon for the quantification of volume changes in ductile shear zones cutting plutonic rocks     

Robert Sturm  Hans Peter Steyrer 《Chemie der Erde / Geochemistry》2003,63(1):31-54

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