Sand flux estimation during a sand-dust storm at Tazhong area of Taklimakan Desert, China

In this paper, the sand transport during a sand-dust storm in the Tazhong area of the central Taklimakan Desert from 11：29 to 23：56 on July 19, 2008 was observed and measured in real time. The sand flux at Tazhong was estimated using sand transport empirical formulas. The critical friction velocity at Tazhong was 0.24 m/s and the functional relation between the wind speed and sediment discharge at the height of 2 m was established. It was also found that the calculated values by Lettau＇s sediment discharge formula were close to those of the instrument measurements. The horizontal sand flux and the vertical sand flux during this sand-dust storm at Tazhong were respectively 258.67×10-4 kg/（m·s） and 40.07×10-7 kg/（m2·s）.

Wind tunnel test on the effect of metal net fences on sand flux in a Gobi Desert, China

The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding effect of the sand-blocking fence is below the expectation. In this study, effects of metal net fences with porosities of 0.5 and 0.7 were tested in a wind tunnel to determine the effectiveness of the employed two kinds of fences in reducing wind velocity and restraining wind-blown sand. Specifically, the horizontal wind velocities and sediment flux densities above the gravel surface were measured under different free-stream wind velocities for the following conditions： no fence at all, single fence with a porosity of 0.5, single fence with a porosity of 0.7, double fences with a porosity of 0.5, and double fences with a porosity of 0.7. Experimental results showed that the horizontal wind velocity was more significantly decreased by the fence with a porosity of 0.5, especially for the double fences. The horizontal wind velocity decreased approximately 65% at a distance of 3.25 m（i.e., 13 H, where H denotes the fence height） downwind the double fences, and no reverse flow or vortex was observed on the leeward side. The sediment flux density decreased exponentially with height above the gravel surface downwind in all tested fences. The reduction percentage of total sediment flux density was higher for the fence with a porosity of 0.5 than for the fence with a porosity of 0.7, especially for the double fences. Furthermore, the decreasing percentage of total sediment flux density decreased with increasing free-stream wind velocity. The results suggest that compared with metal net fence with a porosity of 0.7, the metal net fence with a porosity of 0.5 is more effective for controlling wind-blown sand in the expansive windy area where the Lanzhou-Xinjiang High-speed Railway runs through.

A laboratory test of the electrification phenomenon in wind-blown sand flux

The measured data in the wind-tunnel tests show that the wind-blown sand particles acquired a negative charge when their diameters are smaller than 250 μm and positive charge when their diameters are larger than 500 μm, which confirms Latham’s assumption that the large particles in wind-blown sand flux acquired positive charge while negative charge developed on small ones. In the meanwhile, the measured data also show that the average charge-to-mass ratio for wind-blown sand particles decreases with the increase of the particle diameter and the wind velocity, and increases with the rise of height. The electric field in wind-blown sand flux is mainly formed by the moving charged sand particles. Its direction is vertical to the Earth’s surface and upward, which is opposite to that of the fair-weather field. The electric field increases with wind velocity and height increasing. These experimental results will lay the foundation for developing the theoretical analysis of the electrification phenomenon in

Sand flux and wind profiles in the saltation layer above a rounded dune top

The near-bed airflow and the movement of sand dune sediments by wind are fundamental dune geomorphological processes.This research measured the wind profiles and sand mass flux on the rounded top of a transverse dune at the southern edge of the Tengger Desert to examine how to best predict the vertical profile of sand flux.This work also tested the accuracy of previously developed models in predicting the apparent roughness length during saltation.Results show that mass flux vertical distribution over the dune top is underestimated by an exponential function,overestimated by a power function,but closely matches the predictions made using the LgstcDoseRsp function.Given suitable values ofα,βandγaccording to the grain size composition,S?rensen equation with the peaked shape of the mass transport curve will well predict the dimensionless mass flux qg/ρu*3against dimensionless shear velocity u*/u*t.The modified Charnock model works best of the previously published models tested,with an R2of 0.783 in predicting the enhanced roughness over the moving sand surface,as opposed to an R2of0.758 for the Owen model and an R2of 0.547 for the Raupach model.For the rounded dune top in this study,C m=0.446±0.016.

Sand particle lift-off velocity measurements and numerical simulation of mass flux distributions in a wind tunnel

Lift-off velocity of saltating sand particles in wind-blown sand located at 1.0 mm above the sand bed surface was measured using a phase Doppler particle analyzer in a wind tunnel. The results show that the probability distribution of lift-off velocity can be expressed as a lognormal function, while that of lift-off angle follows an exponential function. The probability distribution of lift-off angle conditioned for each lift-off velocity also follows an exponential function, with a slope that becomes steeper with increasing lift-off velocity. This implies that the probability distribution of lift-off velocity is strongly dependent on the lift-off angle. However, these lift-off parameters are generally treated as an independent joint probability distribution in the literature. Numerical simulations were carried out to investigate the effects of conditional versus independent joint probability distributions on the vertical sand mass flux distribution. The simulation results derived from the conditional joint probability distribution agree much better with experimental data than those from the independent ones. Thus, it is better to describe the lift-off velocity of saltating sand particles using the conditional joint probability distribution. These results improve our understanding of saltation processes in wind-blown sand.

A probability density function of liftoff velocities in mixed-size wind sand flux

With the discrete element method(DEM) ,employing the diameter distribution of natural sands sampled from the Tengger Desert,a mixed-size sand bed was produced and the particle-bed collision was simulated in the mixed-size wind sand movement. In the simulation,the shear wind velocity,particle diameter,incident velocity and incident angle of the impact sand particle were given the same values as the experimental results. After the particle-bed collision,we collected all the initial velocities of rising sand particles,including the liftoff angular velocities,liftoff linear velocities and their horizontal and vertical components. By the statistical analysis on the velocity sample for each velocity component,its probability density functions were obtained,and they are the functions of the shear wind velocity. The liftoff velocities and their horizontal and vertical components are distributed as an exponential density function,while the angular velocities are distributed as a normal density function.

The trend of sand flux and the meteorology elements changes in the near-surface layer of Tengger desert in the spring of 2006

Dust storm events,especially those associated with strong winds,are immediately dangerous,and have long-term harmful effects.During a dust storm event,dust in the near-surface atmospheric layer decreases visibility,and changes local meteorological parameters.In this paper,we analyzed levels of near-surface turbulence during and outside a dust storm event and found differences in the degree of turbulence,with wind speed increasing and amounts of windblown sand greatly increasing air turbu-lence during the dust storms compared with the corresponding values on a sunny day.In addition,the wind profile during the dust storm deviated from the normal profile and became more complex.In the near-surface atmospheric layer,sand and dust flux during the dust storm also differed from those on a sunny day.

Near-surface sand-dust horizontal flux in Tazhong-the hinterland of the Taklimakan Desert

Tazhong is the hinterland and a sandstorm high-frequency area of the Taklimakan Desert. However, little is known about the detailed time-series of aeolian sand transport in this area. An experiment to study the sand-dust horizontal flux of near-surface was carried out in Tazhong from January to December 2009. By measur- ing the sand-dust horizontal flux throughout sixteen sand-dust weather processes with a 200-cm tall Big Spring Number Eight （BSNE） sampler tower, we quantitatively analyzed the vertical variation of the sand-dust horizontal flux. And the total sand-dust horizontal flux of different time-series that passed through a section of 100 cm in width and 200 cm in height was estimated combining the data of saltation movement continuously recorded by piezo- electric saltation sensors （Sensit）. The results indicated that, in the surface layer ranging from 0-200 cm, the inten- sity of sand-dust horizontal flux decreased with the increase of the height, and the physical quantities obeyed power function well. The total sand-dust horizontal flux of the sixteen sand-dust weather processes that passed through a section of 100 cm in width and 200 cm in height was about 2,144.9 kg, the maximum of one sand-dust weather event was about 396.3 kg, and the annual total sand-dust horizontal flux was about 3,903.2 kg. The high levels of aeolian sand transport occurred during daytime, especially from 13：00 to 16：00 in the afternoon. We try to develop a new method for estimation of the detailed time-series of aeolian sand transport.

Effect of the W-beam central guardrails on wind-blown sand deposition on desert expressways in sandy regions

Many desert expressways are affected by the deposition of the wind-blown sand,which might block the movement of vehicles or cause accidents.W-beam central guardrails,which are used to improve the safety of desert expressways,are thought to influence the deposition of the wind-blown sand,but this has yet not to be studied adequately.To address this issue,we conducted a wind tunnel test to simulate and explore how the W-beam central guardrails affect the airflow,the wind-blown sand flux and the deposition of the wind-blown sand on desert expressways in sandy regions.The subgrade model is 3.5 cm high and 80.0 cm wide,with a bank slope ratio of 1:3.The W-beam central guardrails model is 3.7 cm high,which included a 1.4-cm-high W-beam and a 2.3-cm-high stand column.The wind velocity was measured by using pitot-static tubes placed at nine different heights(1,2,3,5,7,10,15,30 and 50 cm)above the floor of the chamber.The vertical distribution of the wind-blown sand flux in the wind tunnel was measured by using the sand sampler,which was sectioned into 20 intervals.In addition,we measured the wind-blown sand flux in the field at K50 of the Bachu-Shache desert expressway in the Taklimakan Desert on 11 May 2016,by using a customized 78-cm-high gradient sand sampler for the sand flux structure test.Obstruction by the subgrade leads to the formation of two weak wind zones located at the foot of the windward slope and at the leeward slope of the subgrade,and the wind velocity on the leeward side weakens significantly.The W-beam central guardrails decrease the leeward wind velocity,whereas the velocity increases through the bottom gaps and over the top of the W-beam central guardrails.The vertical distribution of the wind-blown sand flux measured by wind tunnel follows neither a power-law nor an exponential function when affected by either the subgrade or the W-beam central guardrails.At 0.0H and 0.5H(where H=3.5 cm,which is the height of the subgrade),the sand transport is less at the 3 cm height from the subgrade surface than at the 1 and 5 cm heights as a result of obstruction by the W-beam central guardrails,and the maximum sand transportation occurs at the 5 cm height affected by the subgrade surface.The average saltation height in the presence of the W-beam central guardrails is greater than the subgrade height.The field test shows that the sand deposits on the overtaking lane leeward of the W-beam central guardrails and that the thickness of the deposited sand is determined by the difference in the sand mass transported between the inlet and outlet points,which is consistent with the position of the minimum wind velocity in the wind tunnel test.The results of this study could help us to understand the hazards of the wind-blown sand onto subgrade with the W-beam central guardrails.

再生砂混凝土的吸水与抗氯离子渗透性能影响因素研究

为了探明再生砂混凝土的吸水性能和抗氯离子渗透性能特性,研究了水胶比(0.37、0.45、0.58)、再生砂掺量(0、30%、50%、70%、100%)、再生砂中微粉含量(3%、7%、10%)、矿物掺合料品种和掺量、再生砂预湿程度(0、50%、100%)等因素对再生砂混凝土体积吸水率、软化系数和电通量的影响,对比了不同影响因素对再生砂混凝土吸水性能和抗氯离子渗透性能的影响程度。结果表明:随着再生砂掺量和微粉含量的增加,混凝土的吸水性能增强、耐水性降低、抗氯离子渗透性能下降;而通过掺入多元复合矿物掺合料(15%粉煤灰+15%矿粉+8%硅灰)、降低水胶比和提高再生砂的预湿程度,均能不同程度改善再生砂混凝土的吸水性能和抗氯离子渗透性能。

黄河水沙监测数据分析与模型构建

对黄河水沙监测数据进行分析研究,使用相关性分析、回归分析、Mann-Kendall非参数检验、奇异谱分析等方法构建数学模型.分析含沙量与各因素的关系、水沙通量变化规律、水沙通量趋势预测、河底高程变化规律预测等问题,并提出水沙通量监测的优化策略.在环境治理、调水调沙、防洪减灾等方面具有一定的现实意义.

阻锈剂对海砂淡化工艺影响研究

针对海南近海海域海沙进行淡化研究,获得适于基建要求的淡化海沙工艺。考察了水洗次数、阻锈剂用量对淡化海砂氯离子含量及混凝土离子扩散通量参数影响,获得最佳海沙淡化工艺。研究结果表明,在水洗次数达到3次时,淡化海砂的氯离子含量达到一级淡化海砂标准。水洗次数或阻锈剂含量增加,氯离子含量、离子通量减少;但阻锈剂含量过高会造成材料和易性变差,且对混凝土抗腐蚀性能收效微小。试验确定的因子影响的主次因素依次为:阻锈剂含量,水洗次数。兼顾混凝土和易性,适宜的淡化条件为:水洗3次(m_水∶m湿海砂=1∶2),阻锈剂含量2.0%(相对水泥质量比)。本研究为海南近海海域海沙淡化提供借鉴,为建筑业提供制备合乎基建所需的细骨料原料的方法或工艺。

海砂的淡化及其对水泥砂浆性能的影响

本文采用淡水冲洗法处理海砂,探究淡水冲洗次数以及阻锈剂用量对海砂水泥砂浆试样性能的影响。结果表明,淡化海砂水泥砂浆试样性能随着水洗次数及阻锈剂用量的增加呈现先增加后下降的趋势,当水洗次数为5次时,试样对氯离子的抗渗透性能最佳,具有较好的耐久性和抗腐蚀性能。水洗次数为3次时试样的抗压强度最佳为11.373MPa,达到M10等级,抗折强度最佳为4.844 MPa。当阻锈剂用量为1%时,水泥砂浆试样对氯离子的抗渗透性、抗压性能和抗折性能最佳,其中抗氯离子渗透性和抗折强度相较于未加阻锈剂的试样得到了较为显著的增强。

不同机制砂含量对铁路混凝土性能的影响

天然砂作为混凝土的重要组成部分,对混凝土工作性能、耐久性能起着举足轻重的作用,然而随着我国基础建设加快,天然河砂资源急剧减少。文中研究不同机制砂掺量对混凝土工作性、强度、电通量、气泡间距系数、抗硫酸盐侵蚀系数、抗冻性的影响。结果表明,减水剂、引气剂用量随机制砂掺量增加而增加,56 d抗压强度在机制砂掺量为75%时最高,电通量、气泡间距系数随着机制砂掺量增加呈降低趋势,抗硫酸盐侵蚀系数在机制砂掺量为50%时最低。抗冻性随着机制砂掺量的增加,呈现上升趋势,56 d、75%机制砂抗压强度较天然砂提高4.3%,56 d电通量机制砂较天然砂降低8.8%,56 d气泡间距系数降低8.7%。

抗氯剂对海砂海水混凝土抗氯离子渗透性能影响

目前将海砂应用于混凝土建设主要有两种途径,一是将海砂淡化处理为建筑用砂,二是在混凝土中添加抗氯剂来阻隔氯离子的渗透。通过研究各种抗氯剂对于海砂海水混凝土抗氯离子渗透性能的影响,结果表明:在各种抗氯剂中,偏高岭土和甲基硅酸钠效果最为明显,与不加抗氯剂的样品对比,其电通量分别降低了33.6%和41.6%,且对混凝土短期强度和长期强度均无影响。

保护性耕作农田地表风沙流特性

土壤风蚀是中国北方干旱半干旱地区农田土地退化的重要原因。该文利用移动式风蚀风洞对保护性耕作农田和传统翻耕农田进行原位测试,对比分析保护性耕作农田地表风沙流特性,探讨保护性耕作对土壤风蚀的影响机理,为防治农田土壤风蚀提供理论依据。研究表明,与对照秋翻地相比,由于直立残茬的作用,保护性耕作农田能迅速降低近地表风速,特别是在残茬高度内改变了风速随高度变化的对数规律,风速随高度的降低而急剧减小。其风沙流结构也发生了明显变异,风沙活动层主要集中在180～400mm高度范围内,占总输沙量的67.94%～69.28%,最大输沙率出现在距地表240mm高度上,风沙流结构呈现出类似象鼻形状的"象鼻效应"。风沙流总输沙率也明显小于对照秋翻地,保护性耕作是一种防治农田风蚀沙化的有效耕作措施。

关于风沙流中风速廓线的进一步实验研究

总结与分析了以前学者对风沙流中风速廓线的研究成果,指出了其中的不足之处。并通过实验测出两种较典型自然沙(沙丘沙与河滩冲积沙)所形成稳定状态下风沙流中的风速廓线,提出了新的风速廓线模型。实验结果表明风沙流中的风速廓线用幂函数u=azb拟和最佳,拟合系数均大于0 95。经验证,实验结果可靠。

新月形沙丘表面100cm高度内风沙流输沙量垂直分布函数分段拟合

为研究新月形沙丘表面不同层位风沙流输沙量的垂直分布函数,实测了塔克拉玛干沙漠腹地典型新月形沙丘表面100 cm高度内（以1 cm分隔）的输沙量。分段拟合分析表明：新月形沙丘迎风坡脚输沙量垂直分布规律不完全服从指数函数,出现与戈壁风沙流结构特征相似的＂象鼻效应＂,在0~3 cm区间内输沙量逐渐增大,3cm以上输沙量随高度呈指数函数衰减;沙丘顶部0~10 cm区间输沙量随高度呈指数函数衰减,10 cm以上呈二次函数衰减;沙丘左翼端输沙量随高度呈幂函数分布,沙丘右翼端0~20 cm内以指数函数衰减,20 cm以上呈三次函数衰减;沙丘背风坡脚风沙流输沙量在0~60 cm和60 cm以上分别呈不同形式的三次函数分布。

戈壁风沙流结构和风速廓线特征研究

通过对戈壁地表风沙流特性的风洞模拟实验,旨在探讨戈壁地表性质是如何影响气流的紊动性,并对风沙流的结构和风沙活动层内的风速廓线产生影响,从而对野外风沙工程的设计提供理论依据。实验发现:在戈壁地表风沙活动层主要集中在距地表20cm范围内;由于沙颗粒与戈壁地表的砾石发生碰撞,浓度分布不再简单的服从对数关系递减,其极值出现的高度随风速的增加而上移,呈现"象鼻效应";不同风速下风沙活动层内同一高度含沙颗粒浓度之间存在很好的相关性。

近地表风沙流结构对过渡带不同下垫面的响应

在塔克拉玛干沙漠南缘策勒绿洲—沙漠过渡上选取流动沙地、半流动沙地和固定沙地3个典型下垫面,利用梯度集沙仪测定其近地表10cm的风沙流结构。结果表明,流动沙地地表0~1cm的沙粒百分含量随着风速的增大而减小;2~10cm的沙通量随着风速的增大其百分含量增加,1~2cm的沙通量存在一个稳定层,幂函数、指数函数和对数函数均能较好地反映其沙通量垂直分布特征,并可以利用风沙流结构来判定地表的蚀积状况;半固定和固定沙地地表由于受到植被盖度影响,其风沙流结构特征表现为近地表0~1cm沙通量较流动沙地少,2~10cm的沙通量百分含量较多,且每层沙通量与风速的相关性较差,稳定层在植被盖度的扰动下抬高或者消失,对数函数能较好地反映其风沙流结构特征,地表蚀积状况不可用现存风沙流结构地表蚀积公式来判定。