珠江三角洲场地震害预测   总被引：3，自引：2，他引：3  

郭软华  梁致荣 《华南地震》1995,15(3):22-33

场地震害是随空间和时间而变化的多因子影响的综合体。本文根据这一观点分析影响珠江三角洲场地震害的环境因子及岩土特征，探讨该区砂土液化、软土震陷、活动断裂、滑坡、崩塌、岩溶和孤立地形等场地震害，指出本区未来场地震害的主要形式是砂土液化和软土震陷，但也不可忽视活动断裂和水下场地震害，以及特殊地形地貌引致的共振、驻波破坏。  相似文献   

广东沿海的晚更新世沙坝   总被引：6，自引：0，他引：6  

刘尚仁 《地理科学》1995,15(3):281-288

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砂土液化的尺度与概率     

刘颖  李大华 《地震研究》1993,16(2):193-198

本文以液化安全间距及安全系数为随机变量进行了可靠性分析,给出了衡量砂土液化严重程度的尺度及相应的液化概率,并提出了对砂土液化严重程度进行分级的建议。  相似文献   

Monitoring alluvial sand suspension by eddy correlation     

Michel Lapointe 《地球表面变化过程与地形》1993,18(2):157-175

Eddy correlation techniques are standard tools in micrometeorology and oceanography to measure momentum and contaminant transport across turbulent boundary layers. They can, in theory, be used to estimate the net vertical suspended sediment flux directly over different areas of an alluvial channel boundary, and thus disclose ongoing erosion/deposition patterns. The basic principles and main problems in applying the technique to alluvial suspension are first introduced. Results from a trial application of the method in a large sand bed river are then presented; the focus of the analysis is on the substantial (and surprising) contributions of multi-minute flow fluctuations to suspension work in the study environment. The data were collected in a 10 m deep channel of the Fraser River near Mission, British Columbia, Canada. Turbulent fluctuations of flow components streamwise and normal to the bed, along with the output of an optical suspended sediment sensor, were monitored over 7 h, 1 m above the bed. Flow velocities averaged 0·9 ms^?1 and mean suspended sediment concentrations 500 mgl^?1, at sensor level above 1–5 dm high dunes. Spectral analysis of the records reveals that approximately 30 per cent of the vertical suspended sand mixing across the sensor level (and roughly as much of the momentum exchange) was linked to gradual flow oscillations with periods between 1 and 13·6 min (underlying briefer, turbulent fluctuations). Extended periods of sediment-rich, slightly upward directed but slower mean flow alternated with periods of sediment-poor, slightly downward and faster mean flow; these slow fluctuations involved 10–20 cms^?1 changes in 5 min average flow speed, 2–4· changes in vertical flow angle and 100 mgl^?1 changes in mean sand concentration. To obtain accurate eddy-correlation estimates of the vertical suspension flux in the study conditions, hour-scale flow and turbidity records that include many of these multi-minute cycles appear to be necessary. The spectra of the Fraser River near-bed signals do not conspicuously differ in overall shape (in terms of low-frequency content and location of peak) from turbulent spectra encountered in some atmospheric boundary layers. Nonetheless, the long period fluctuations observed on the Fraser River may not be turbulent; rather they may reflect slowly evolving perturbations in the near-bed streamlines, caused by bedform translation or gradual fluctuation within the large-scale streamwise cells of the secondary flow.  相似文献   

Case histories of sand search in the Niger Delta     

T.?K.?S.?AbamEmail author 《Environmental Geology》2004,46(2):165-172

This paper discusses the imperatives of sand search and describes two case histories of sand search in the Niger Delta. These case histories highlight the project cycle of sand search operations and circumstances in which environmental peculiarities can influence procedures and strategies. Field and laboratory procedures emphasise the applications of particle-size distribution and compaction tests to field construction control. The need to integrate mitigative measures of potential impacts into the planning and execution of projects has been emphasised. Some environmental consequences of sand dredging have also been highlighted.  相似文献   

Mobility of a remobilised parabolic dune in Kennemerland, The Netherlands   总被引：5，自引：0，他引：5  

S. M. Arens  Q. Slings  C. N. de Vries 《Geomorphology》2004,59(1-4):175

A parabolic dune in the Netherlands was remobilised in December 1998 by removing vegetation and soil. The main aim of the experiment was ecological: to investigate whether permanent rejuvenation at the landscape scale is possible by restoration of natural processes. If processes can be reactivated at coarse scale, periodic rejuvenation of the landscape over the long term is possible, without the need for managers to interfere further. The experiment provides the opportunity to address another important question: can large parabolic dunes in the Netherlands be mobile in the present climate? Mobility of the dune is investigated by means of erosion pins, aerial photography and measurement of cross sections. Activity indices are derived from erosion pin recordings and correlated to weather conditions. From 1999 to 2001, displacement of the dune ranged from 0 to 12 m in east–northeasterly direction. Activity of the dune is related to wind conditions, but the relationship is strongly influenced by precipitation and therefore differs for wet and dry periods. Periods with extreme wind speeds resulted in much less geomorphic change than expected.  相似文献   

Movement of a small slipfaceless dome dune in the Namib Sand Sea, Namibia     

C. S. Bristow  N. Lancaster   《Geomorphology》2004,59(1-4):189

The migration of a small slipfaceless dome dune close to the northern edge of the Namib Sand Sea has been measured by topographic survey. The dune dimensions are 45-m wide and 1-m high with a volume of 551 m³ that has been calculated as the difference between the dune's surface elevation and an interdune surface extrapolated from measurements around the edge of the dune. The migration direction, 64°, and distance moved, 90 m, are measured against stakes set out in 1976. The dune has moved about 90 m between 1976 and 1999. This is an average linear migration rate of around 4 m year⁻¹, and is equivalent to an annual sand transport rate of about 1.2 tonnes m⁻¹ year⁻¹. The calculated total potential sand flow in this part of the Namib Desert is 119 tonnes m⁻¹ year⁻¹, and the resultant potential sand flow is 63 tonnes m⁻¹ year⁻¹. The dune migration is therefore about 1% of the total potential sandflow and 2% of the resultant indicating that dune migration is only a small part of total potential sand transport. The results suggest that small slipfaceless dome dunes are very inefficient at trapping sand, and that winds blowing across the interdune in this area are undersaturated with sand.  相似文献   

Early growth of the last Cordilleran ice sheet deduced from glacio-isostatic depression in southwest British Columbia, Canada     

John J. Clague  Duane Froese  Ian Hutchinson  Karen M. Simon 《Quaternary Research》2005,63(1):53-59

Relative sea level at Vancouver, British Columbia rose from below the present datum about 30,000 cal yr B.P. to at least 18 m above sea level 28,000 cal yr B.P. In contrast, eustatic sea level in this interval was at least 85 m lower than at present. The difference in the local and eustatic sea-level positions is attributed to glacio-isostatic depression of the crust in the expanding forefield of the Cordilleran ice sheet during the initial phase of the Fraser Glaciation. Our findings suggest that about 1 km of ice was present in the northern Strait of Georgia 28,000 cal yr B.P., early during the Fraser Glaciation.  相似文献   

Experimental evidence of a unique flow rule of non-cohesive soils under high-cyclic loading     

T. Wichtmann  A. Niemunis  Th. Triantafyllidis 《Acta Geotechnica》2006,1(1):59-73

The presented results of cyclic triaxial tests on sand demonstrate that the cumulative effects due to small cycles obey a kind of flow rule. It mainly depends on the average stress ratio about which the cycles are performed. This so-called “cyclic flow rule” is unique and can be well approximated by flow rules for monotonic loading. Amongst others it is shown that the cyclic flow rule is only moderately influenced by the average mean pressure, by the strain loop (span, shape, polarization), the void ratio, the loading frequency, the static preloading and the grain size distribution curve. A slight increase of the compactive portion of the flow rule with increasing residual strain (due to the previous cycles) was observed. These experimental findings prove that the cyclic flow rule is an essential and indispensable concept in explicit (N-type) accumulation models.  相似文献   

Large-eddy Simulation of the Dispersion of Solid Particles in a Turbulent Boundary Layer   总被引：2，自引：2，他引：2  

Ivana Vinkovic  Cesar Aguirre  Michel Ayrault  Serge Simoëns 《Boundary-Layer Meteorology》2006,121(2):283-311

A large-eddy simulation (LES) with the dynamic Smagorinsky-Germano subgrid-scale (SGS) model is used to study the dispersion of solid particles in a turbulent boundary layer. Solid particles are tracked in a Lagrangian way. The instantaneous velocity of the surrounding fluid is considered to have a large-scale part (directly computed by the LES) and a small-scale part. The SGS velocity of the surrounding fluid is given by a three-dimensional Langevin model written in terms of SGS statistics at a mesh level. An appropriate Lagrangian correlation time scale is considered in order to include the influences of gravity and inertia of the solid particle. Inter-particle collisions and the influence of particles on the mean flow are also taken into account. The results of the LES are compared with the wind-tunnel experiments of Nalpanis et al. (1993 J Fluid Mech 251: 661–685) and of Tanière et al. (1997 Exp in Fluids 23:463–471) on sand particles in saltation and in modified saltation, respectively.  相似文献