毛乌素沙漠风积砂力学特性室内试验研究

在对毛乌素沙漠风积砂物理特性进行试验研究的基础上,通过室内击试验、压缩试验及三轴剪切试验,对毛乌素沙漠风积砂的力学特性进行了初步研究。结果表明:毛乌素沙漠风积砂击实特性与粉、黏性土有较大的差异,在干燥和最佳含水率状态下易于击实,击实曲线呈双峰形态;压缩试验表明毛乌素沙漠风积砂一般属于低压缩性土,其压缩特性与试样初始密度、含水率、荷载级别及加载条件有关;三轴剪切试验表明毛乌素沙漠风积砂抗剪强度指标受试样密度的影响较大,虽然含水率对抗剪强度指标有一定影响且具有一定规律性,但影响程度并不明显。本文相关成果为解决该区风积砂相关岩土工程问题和工程地质问题提供了可靠的试验依据。     

Transport and dispersal of organic debris (peat blocks) in upland fluvial systems

This paper assesses the mechanisms and pathways by which peat blocks are eroded and transported in upland fluvial systems. Observations and experiments from the north Pennines (UK) have been carried out on two contrasting river systems. Mapping of peat block distributions and appraisal of reach‐based sediment budgets clearly demonstrates that macro‐size peat is an important stream load component. In small streams block sizes can approximate the channel width and much of the peat is transported overbank. Local ‘peat jams’ and associated mineral deposition may provide an important component of channel storage. In larger systems peat blocks rapidly move down‐channel and undergo frequent exchanges between bed and bank storage. Results of peat block tracing using painted blocks indicate that once submerged, blocks of all sizes are easily transported and blocks break down rapidly by abrasion. Vegetation and bars play an important role in trapping mobile peat. In smaller streams large block transport is limited by channel jams. Smaller blocks are transported overbank but exhibit little evidence of downstream fining. In larger rivers peat blocks are more actively sorted and show downstream reduction in size from source. A simple model relating peat block diameter (D_p) to average flow depth (d) suggests three limiting transport conditions: flotation (D_p < d), rolling (d < D_p > d/2) and deposition (D_p > d/2). Experiments demonstrate that peat block transport occurs largely by rolling and floating and the transport mechanism is probably controlled by relative flow depth (d/D_p ratio). Transport velocity varies with transport mechanism (rolling is the slowest mode) and transport lengths increase as flow depth increases. Abrasion rates vary with the transport mechanism. Rolling produces greater abrasion rates and more rounded blocks. Abrasion rates vary from 0 to 10 g m^?1 for blocks ranging in mass from 10 to 6000 g. Copyright © 2001 John Wiley & Sons, Ltd.     

The factors influencing the abrasion efficiency of saltating grains on a clay‐crusted playa

The entrainment and subsequent transport of PM₁₀ (particulate matter <10 µm) has become an important and challenging focus of research for both scientific and practical applications. Arid and semi‐arid environments are important sources for the atmospheric loading of PM₁₀, although the emission of this material is often limited by surface crusts. It has been suggested that the primary mechanisms through which PM₁₀ is released from a crusted surface are abrasion by saltating grains or disturbance by agricultural and recreational activities. To examine the importance of saltation abrasion in the emission of PM₁₀, a series of field wind tunnel tests were conducted on a clay‐crusted surface near Desert Wells, Arizona. In a previous part of this study it was found that the emission rate varies linearly with the saltation transport rate, although there can be considerable variation in this relationship. This paper more closely examines the source of the variability in the abrasion efficiency, the amount of PM₁₀ emitted by a given quantity of saltating grains. The abrasion efficiency was found to vary with the susceptibility of the surface to abrasion, the ability of the sand to abrade that surface and the availability of material with a caliper size <10 µm within the crust. Specifically, the results of the study show that the abrasion efficiency is related to the crust strength, the amount of surface disturbance and the velocity of the saltating grains. It is concluded that the spatial and temporal variability of these controls on the abrasion efficiency imposes severe contextual limitations on experimentally derived models, and can make theoretical models too complex and impractical to be of use. Copyright­© 2001 John Wiley & Sons, Ltd.     

Rates of rock surface lowering,Princess Elizabeth land,Eastern Antarctica

A series of micro-erosion-meter sites on different rock types and in differing wind regimes was established and re-read after four years on two sites in the Larsemann and Vestfold Hills. These two oases in Eastern Antarctica are subjected to both wind abrasion and salt wedging. The measurements displayed bimodal distributions, indicating that both abrasion and single-grain detachment could be observed. Surface lowering rates of 0·015 and 0·022 mm a^?1 were demonstrated for the Larsemann and Vestfold Hills, respectively.     

线形沙丘的风沙沉积特征与内部构造

本文介绍了线形沙丘不同部位风沙沉积物的粒度特征、易溶盐含量特征和颗粒形态特征，通过现场全断面开挖线形沙丘剖面，对线形沙丘的内部构造进行了观测，结合研究地区的风信资料，对线形沙丘的风沙堆积过程进行了初步分析研究。     

大牛地气田钻杆耐磨环失效原因分析

鄂尔多斯北部大牛地地区钻井施工中钻杆偏磨、耐磨环失效现象很普遍。通过对比分析研究,认为造成钻杆耐磨环失效的主要原因有:地层研磨性、钻杆的井下工况、耐磨材料选择与敷焊工艺的影响。     

Sonic anemometers in aeolian sediment transport research

Fast-response wind and turbulence instruments, including sonic anemometers, are used more and more in aeolian sediment transport research. These instruments give information on mean wind, but also on fluctuations and turbulent statistics, such as the uw covariance, which is a direct measure of Reynolds' stress (RS) and friction velocity. This paper discusses the interpretation of sonic anemometer data, the transformations needed to get proper results and turbulence spectra, and how they are influenced by instrument size, sampling frequency, and measurement height.Turbulence spectra characterize how much the different frequencies in the turbulent signals contribute to the variance of wind speed, or to the covariance of horizontal and vertical wind speed. They are important in determining the measurement strategy when working with fast-response instruments, such as sonic anemometers, and are useful for interpreting the measurement results. Choices on the type of sonic anemometer, observation height, sampling period, sampling frequency, and filtering can be made on the basis of expected high and low-frequency losses in turbulent signals, which are affected by those variables, as well as wind speed and atmospheric stability.Friction velocity and RS, important variables in aeolian sediment transport research, are very sensitive to tilt or slope errors. During a field experiment, the slope sensitivity of the RS was established as 9% per degree of slope, which is 1.5 times the value reported in literature on the basis of theoretical considerations. An important reason for the difference probably is the large influence of streamline curvature on turbulence statistics and thereby on the slope sensitivity of the RS. An error of 9% per degree of slope in the RS will translate into an error of approximately 4% per degree of slope in the calculated friction velocity.Space–time correlation of the horizontal wind speed is much larger than that of the vertical wind speed and the instantaneous RS. This largely explains why, in previous studies, a poor correlation was found between instantaneous RS measured at 3 m height and saltation flux near the surface, whereas the correlation between wind speed at some height and saltation flux was much better. Therefore, the poor correlation between RS away from the surface and saltation flux does not contradict that saltation flux is caused by RS.     

A comparison of methods used to estimate the height of sand dunes on Mars

The collection of morphometric data on small-scale landforms from other planetary bodies is difficult. We assess four methods that can be used to estimate the height of aeolian dunes on Mars. These are (1) stereography, (2) slip face length, (3) profiling photoclinometry, and (4) Mars Orbiter Laser Altimeter (MOLA). Results show that there is good agreement among the methods when conditions are ideal. However, limitations inherent to each method inhibited their accurate application to all sites. Collectively, these techniques provide data on a range of morphometric parameters, some of which were not previously available for dunes on Mars. They include dune height, width, length, surface area, volume, and longitudinal and transverse profiles. The utilization of these methods will facilitate a more accurate analysis of aeolian dunes on Mars and enable comparison with dunes on other planetary surfaces.     

The upper pleistocene loess of southern Tunisia: A statement

On the Matmata Plateau, the sedimentological characteristics of the peri-desert loess and the interbedded palaeosols (particle-size distribution; chemical and mineralogical composition of major components; trace elements; clay mineral assemblage; heavy mineral assemblage; SEM-examined surficial textures of the quartz and palygorskite grains) show notable homogeneity: they also indicate its allochthonous origins (the main sedimentary source being the Great Eastern Erg), its transport as an aeolian suspension sediment prior to deposition, and moderate pedogenesis acting during deposition. The emplacement of the loess was synchronous with a ‘pluvial’ steppe palaeoenvironment moister than at present, as shown by ¹⁸O and ¹³C data. The palaeosols point to a weak pedogenesis and colluvial and alluvial reworking that were contemporary with the aeolian deposition. ¹⁴C radiometric dating suggests a main period of pluvial dust-fall/loess deposition in the Upper Pleistocene (until 10 000 yr BP) and a shorter one in the Middle Holocene.     

Using quartz grain size and shape analysis to distinguish between aeolian and fluvial deposits in the Dallol Bosso of Niger (West Africa)

Size and Fourier-shape characteristics of quartz sand grains were determined by computerized image analysis in order to distinguish between aeolian and fluvial soil parent materials in the Dallol Bosso in Niger. Factor analysis of grain-size distributions gave four sand end-members that can be related to fluvial transport dynamics operating when the sediments were initially deposited. The medium to fine (and more angular shaped) sand fractions are being reworked by wind. Aeolian deposits were well sorted whereas fluvial deposits were poorly sorted in both size and shape. Although gross-shape characteristics (lower harmonics of Fourier series expansion) indicated a common source rock for all sands, the aeolian sands were well rounded whereas the fluvial sands tended to be more angular (upper harmonics of Fourier series).