Factors affecting the nature and rate of dust production from natural dune sands

This paper evaluates the influence of natural sand particle characteristics on the amount and particle-size distributions of dust produced by aeolian abrasion. It contrasts with previous studies of aeolian abrasion by conducting experiments using: (i) whole sand samples, as opposed to selected size fractions; (ii) natural, mature dune sands, rather than artificial or freshly crushed material; and (iii) weathered sands that have acquired a superficial clay coating, instead of grains with clean surfaces. Whilst previous research has found clear, positive relationships between particle size, sorting, roundness and the amount of dust produced by aeolian abrasion, the relationships determined in this study show some variation according to the geomorphological context from which the original samples were obtained. The most important factor affecting the amount and particle-size characteristics of the dust produced was the presence of a clay coating on the grain surface that is removed by the abrasion process. The dust produced by this mechanism had a modal size of 2–5  μ m and material <10  μ m comprised up to 90% of the particles produced.     

Assessing the engineering properties of concrete made with fine dune sands: an experimental study

Sand dunes cover an area of 16.6% of the total area of Egypt. This paper presents the results of an extensive laboratory testing that was carried out to determine the engineering properties of concrete. The concrete fine aggregate is fine dune sands obtained from three sites in the Kharga Oasis, Western Desert, Egypt. All samples were classified as poorly graded sand according to the Unified Soil Classification system. Fineness modulus values of the studied dune sands range from 0.89 to 0.97. The percentage of sulfates and chlorides are very low and nearly negligible. Sodium and calcium hydroxides were recorded in some samples with scarce concentration. Organic impurities were not recorded. The degree of workability of the studied dune sands ranged from low to medium, which are suitable for normal reinforced work without vibration and heavily reinforced section with vibration. The measured compressive strength of concrete decreases with increasing dune sand content.     

Morphometric analysis of slipface processes of an aeolian dune: Implications for grain‐flow dynamics

Grain flows are an integral part of sand dune migration; they are a direct response to the local wind regime and reflect complex interactions between localized over‐steepening of a dune slipface and complex turbulent airflow on the lee slope. Grain flows are primarily responsible for delivering sediment to the base of a dune, thus driving slipface advancement; yet, there are few constraints on their morphological and spatial characteristics or the amount of sediment that is redistributed by these flows. Using a combination of high‐resolution terrestrial laser scanning and video recordings, four distinct grain‐flow types are identified based on morphology and area on a dune slipface. Grain‐flow morphologies range from small, superficial flows to larger flows that affect greater portions of the slipface, moving significant amounts of sediment. Detailed field observations are presented of the dynamics of lee slopes, including measurements of the initiation location, thickness, magnitude and frequency statistics of grain flows, as well as volume estimates of redistributed sediment for each grain flow observed. High‐resolution laser scans enable accurate quantification of bulk sediment transfer from individual grain flows and can be used to study grain flows in a variety of environments. A categorization of grain‐flow morphologies is presented that links styles of flows with wind strength and direction, turbulent airflow, sediment deposition and environment.     

Development of a cliff-top dune indicated by particle size and geochemical characteristics: Rubjerg Knude, Denmark

Particle size and geochemical data have been used to investigate the development of a large cliff-top dune at Rubjerg Knude, located on the western coast of Jutland, Denmark. Textural parameters and geochemical ratios provided useful indicators of the dune sediment provenance and mode of evolution of the dune. The dune sediments themselves showed no significant spatial particle size trends and reflect a number of processes, including grainfall, wind-ripple migration and avalanching (grainflow), which formed a high proportion of the deposits on both the stoss and lee sides of the present dune. Fine grainfall sediments, which have accumulated to form a sandplain in the lee of the dune, show fining and improved sorting with distance, and extend more than 2 km downwind of the dune crest. Comparison of the textural and geochemical data from Rubjerg Knude and other locations on the Jutland coast indicates that, although there is a contribution of sand to the dune from local marine sources, the main source of sand to the cliff-top dune and sand plain sediments has been provided by the wind erosion of the underlying cliffs, which are composed of Weichselian age sandy glaciofluvial and glaciolacustrine deposits. Optically stimulated luminescence dating indicated an apparent age for the sand at the base of 274 ± 14 years. If this date is reliable, it suggests that accumulation of the aeolian sand in this area began within approximately the last 300 years. Map and photographic evidence indicate that the modern high dune only began to form after 1885, apparently associated with an acceleration in the rate of coastal cliff retreat.     

Stratigraphic evolution and preservation of aeolian dune and damp/wet interdune strata: an example from the Triassic Helsby Sandstone Formation, Cheshire Basin, UK

Abstract New and previously published models of wet aeolian system evolution form a spectrum of types that may be explained in terms of aeolian dune dynamics, rate of water table rise and/or periodicity of interdune flooding. This is illustrated with an example from the Mid‐Triassic (Anisian) Helsby Sandstone Formation, Cheshire, UK. Lenses of damp and wet interdune strata exhibit an intertonguing, transitional relationship with the toe‐sets of overlying aeolian dune units. This signifies dune migration that was contemporaneous with water table‐controlled accumulation in adjacent interdunes. Downwind changes in the geometry and facies of the interdune units indicate periodic expansion and contraction of the interdunes in response to changes in the elevation of the groundwater table and episodic flooding, during which accumulation of dune strata continued relatively uninterrupted. This contrasts with other models for accumulation in wet aeolian systems where interdune flooding is associated with a cessation in aeolian bedform climbing and the formation of a bypass or erosional supersurface. Architectural panels document the detailed stratigraphy in orientations both parallel and perpendicular to aeolian transport direction, enabling a quantitative three‐dimensional reconstruction of genetically related aeolian dune and interdune elements. Sets of aeolian dune strata are composed of grainflow and translatent wind‐ripple strata and are divided by a hierarchy of bounding surfaces originating from oblique migration of superimposed dunes over slipfaceless, sinuous‐crested parent bedforms, together with lee‐slope reactivation under non‐equilibrium flow conditions. Silty‐mudstone and sandstone interdune units are characterized by wind ripple‐, wavy‐ and subaqueous wave ripple‐laminae, desiccation cracks, mud flakes, raindrop imprints, load casts, flutes, intraformational rip‐up clasts and vertebrate and invertebrate footprint impressions and trackways. These units result from accumulation on a substrate that varied from dry‐ through damp‐ to wet‐surface conditions. Interdune ponds were flooded by either fluvial incursions or rises in groundwater table and were periodically subject to gradual desiccation and reflooding. Red silty‐mudstone beds of subaqueous origin pass laterally into horizontally laminated wind‐ripple beds indicating a progressive transition from wet‐ through damp‐ to dry‐surface conditions within a single interdune.     

Particle size distribution analysis of sand-sized particles by laser diffraction: an experimental investigation of instrument sensitivity and the effects of particle shape

Laser diffraction is now widely used for particle size distribution analysis of sediments and soils. The technique can be very precise, and offers advantages of speed and cost over many other methods when used to analyse mixtures of sand, silt and clay. This study presents the results of an experimental investigation that examined the sensitivity of the Beckman-Coulter LS230 instrument to mixtures of different grain populations and differences in particle shape. The instrument was found to have high sensitivity to coarse particles in a finer matrix (detection threshold 1–2%), but much lower sensitivity to finer particles in a coarser mixture (detection threshold 12–17%). Experiments using near-spherical ballotini showed that laser analysis provides very similar values to dry sieving for the mean, median and mode, but for a range of natural sand samples values for the mean, median and mode were offset by 8–21%, with an average of ca 15%, compared with sieving. Analysis using a Beckman-Coulter RapidVUE instrument, which provides both size and shape information, provided support for the hypothesis that the differences between laser analysis and sieving are partly attributable to the effects of particle shape. However, an additional factor is the way in which the laser software interprets the optical diffraction data. The software predicts a high degree of log-normality in the size distribution, such that highly skewed, truncated or bimodal samples are poorly represented. Experiments using sieved fractions of ballotini indicated that, even with near-perfectly spherical particles, the particle size distribution predicted by the laser software includes a relatively large percentage of particles outside the sieve class limits.     

利用提钾废渣和粉煤灰制备矿物聚合材料的实验研究

利用富钾岩石提钾后的废渣代替硅酸钠 (钾 )、大部分高岭石和氢氧化钠 (钾 ) ,以粉煤灰为主要原料 ,制备出矿物聚合材料 ,并采用正交实验确定其优化工艺条件为 :煅烧高岭石用量为 10 %～ 15 % ,废渣用量约 35 % ,氢氧化钠用量为 5 %～ 6 %。代表性样品的 7d抗压强度可达到 4 0～ 5 0MPa ,耐酸性、耐碱性分别为 99.99%和 10 0 % ,密度1.77～ 1.88g/cm3 ,收缩率 0 .13%～ 0 .2 8% ,导热系数 0 .4 8～ 0 .5 1W/m·K ,平均硬度 3.4 3。X射线粉末衍射分析表明 ,由铝硅酸盐聚合反应形成的基体相呈非晶态。扫描电镜分析絮凝状的基体相与粉煤灰玻璃体结合紧密 ,从而为制品具备良好的力学性能提供了结构基础。该矿物聚合材料成本低廉 ,同时又能利用粉煤灰等工业固体废物而达到改善环境的目的     

低渗透储层不同流动单元可动流体赋存特征及生产动态分析——以鄂尔多斯盆地姬塬地区长6段储层为例

利用高压压汞、恒速压汞、核磁共振、铸体薄片、物性等分析测试手段及试油资料,对姬塬地区长6段储层进行了流动单元的划分,同时分析不同流动单元微观孔隙结构特征及其对可动流体饱和度的影响,进而研究其生产动态的差异。结果表明:研究区四类流动单元微观孔隙结构差异明显,是造成其可动流体饱和度差异的主要因素。其中,喉道半径分布形态及主流喉道半径大小起了决定性作用。在油气田开发阶段中,应该根据不同流动单元的微观孔隙结构差异性特征,实施合理有效的开发方案。