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1.
Abstract Reliable predictions of wind erosion depend on the accuracy of determining whether erosion occurs or not. Among the several factors that govern the initiation of soil movement by wind, surface moisture is one of the most significant. Some widely used models that predict the threshold shear velocity for particle detachment of wet soils by wind were critically reviewed and evaluated. Wind‐tunnel experiments were conducted on pre‐wetted dune sand with moisture contents ranging from 0·00 to 0·04 kg kg?1. Sand samples were exposed to different wind speeds for 2 min. Moisture content was determined gravimetrically before and after each experiment, and the saltation of sand particles was recorded electronically with a saltiphone. Shear velocities were deduced from the wind speed profiles. For each moisture content, the experiments were repeated at different shear velocities, with the threshold shear velocity being determined by least‐squares analysis of the relationships between particle number rates and shear velocity. Within the 2‐min test runs, temporal changes in particle number rates and moisture contents were detected. A steep increase in the threshold shear velocity with moisture content was observed. When comparing the models, large differences between the predicted results became apparent. At a moisture content of 0·007 kg kg?1, which is half the moisture content retained to the soil matrix at a water tension (or matric potential) of ?1·5 MPa, the increase in ‘wet’ threshold shear velocity predicted with the different models relative to the dry threshold shear velocity ranged from 117% to 171%. The highest care should therefore be taken when using current models to predict the threshold shear velocity of wet sediment. Nevertheless, the models of Chepil (1956; Proc. Soil Sci. Soc. Am., 20, 288–292) and Saleh & Fryrear (1995; Soil Sci., 160, 304–309) are the best alternatives available.  相似文献   

2.
The present study aims to investigate the relationships between several soil parameters (texture, organic matter and CaCO3 content) and the threshold wind velocity and erodibility of different soil types. Our aim was to determine the role of these soil parameters play in soil loss due to wind erosion and also to statistically evaluate these correlations. The erodibility studies were carried out in wind tunnel experiments, and the resulting data were analysed with multiple regression analysis and the Kruskal-Wallis test. We found that both the threshold wind speed and the erodibility of soils were mostly determined by silt fraction (0.05–0.02 mm), while sand fractions had a lesser effect on it. Our experiences with organic matter and CaCO3 similar, i.e. in spite of their correlation with the erosion, their contribution was not significant in the multivariate regression model. Consequently, based on mechanical composition of soils, one can predict threshold wind velocity and erodibility of soils.  相似文献   

3.
ＩＮＴＲＯＤＵＣＴＩＯＮＬａｒｇｅａｒｅａｓｏｆａｒｉｄａｎｄｓｅｍｉａｒｉｄｒｅｇｉｏｎｓｏｆｔｈｅｗｏｒｌｄａｒｅａｆ ｆｅｃｔｅｄｂｙｗｉｎｄｅｒｏｓｉｏｎ .Ａｐｐｒｏｘｉｍａｔｅｌｙ 2 8.4%ｏｆｔｈｉｓａｒｅａａｒｅａｆｆｅｃｔｅｄｂｙｓｅｖｅｒｅａｎｄｖｅｒｙｓｅｖｅｒｅｗｉｎｄｅｒｏｓｉｏｎ (Ｋａｔｅｓｅｔａｌ.,1977) .ＩｎＩｒａｑ ,ｔｈｅａｒｉｄａｎｄｓｅｍｉａｒｉｄｒｅｇｉｏｎｓｒｅｐｒｅｓｅｎｔｎｅａｒｌｙ 75%ｏｆｔｈｅｔｏｔａｌｌａｎｄ .5 0 %ｏｆｔｈｉｓｌａｎｄｉｓｓｕｂｊｅｃ…  相似文献   

4.
文章对近年来基于生物固土技术的防风固沙研究进行了回顾和分析。常用于防风固沙的生物过程包括基于微生物或酶诱导碳酸钙沉积（MICP或EICP）的矿化固土技术,加入黄原胶等生物高聚物作为辅助剂,可获得更好的固土效果。土壤风蚀过程中,除了风力本身,风携带的跃移颗粒对土的撞击,也是侵蚀破坏的重要因素,这在生物固化土风蚀试验中体现明显。生物固化防风固沙的处理过程简单易行,以尿素和钙盐作为处理材料,用细菌或脲酶作为催化诱导媒介,对土体进行单遍喷洒处理即可获得很好的抗风效果。室内抗风试验中,将风蚀速率与临界起动风速两个指标结合是较为合理的评估方法。在室内和现场条件下,表面贯入强度测试可用来快速测定处理效果和抗风性能。目前的现场试验研究表明,生物固化土中植物可以生长,但是极端条件下生长受限。为了将该方法推向实用,需要从多重侵蚀因子作用下的抗风力侵蚀能力、生态恢复能力和现场施工技术等方面进一步研究探索。  相似文献   

5.
Aeolian sand transport results from interactions between the ground surface and airflow. Previous research has focused on the effects on sand entrainment and mass transport of surface features and wind velocity, but the influence of air density, which strongly constrains airflow characteristics and the resulting sand flow, has not been widely considered. In the present study, entrainment, saltation characteristics and transport rates were examined at nine experimental sites ranging in elevation from ?154 m below sea‐level (Aiding Lake) to 5076 m above sea‐level (Tanggula Mountain pass on the Qinghai–Tibetan plateau). At each site, a portable wind tunnel and high‐speed camera system were set up, and the friction wind velocity, threshold friction velocity and sand flow structure were observed systematically. For a given volumetric airflow, lower air density increases the wind velocity. Low air density also creates a high threshold friction velocity. The Bagnold wind erosion threshold model remains valid, but the value of empirical parameter A decreased with decreasing air density and ranged from 0·10 to 0·07, the smallest values reported in the literature. For a given wind velocity, increased altitude reduced total sand transport and creeping, but the saltation rate and saltation height increased. The present results provide insights into the fundamental mechanisms of the initiation and transport of sand by wind in regions with an extreme temperature or altitude (for example, alpine deserts and low‐lying lake basins) or on other planets, including Mars. These results also provide theoretical support for improved sand‐control engineering measures. The data and empirical equations provided in this paper improve the ability to estimate threshold and transport conditions for wind‐blown sand.  相似文献   

6.
To understand the generation and development mechanism of soil erosion, data of the wind profile from wind tunnel experiments were used, and the characteristics of the turbulent transmission with free stream velocity and the properties of the surfaces in arid and semi-arid regions were studied by the atmospheric aerodynamic method. The result showed that the turbulent momentum fluxes are proportional to the velocity and the roughness of the surfaces. In addition, they are closely related to the density of the roughness elements; the turbulent exchange coefficient over the near surface layer increases with height.  相似文献   

7.
Geotechnical engineering practice for collapsible soils   总被引：3，自引：0，他引：3  
Conditions in arid and semi-arid climates favor the formation of the most problematic collapsible soils. The mechanisms that account for almost all naturally occurring collapsible soil deposits are debris flows, rapid alluvial depositions, and wind-blown deposits (loess). Collapsible soils are moisture sensitive in that increase in moisture content is the primary triggering mechanism for the volume reduction of these soils. One result of urbanization in arid regions is an increase in soil moisture content. Therefore, the impact of development-induced changes in surface and groundwater regimes on the engineering performance of moisture sensitive arid soils, including collapsible soils, becomes a critical issue for continued sustainable population expansion into arid regions.In practicing collapsible soils engineering, geotechnical engineers are faced with (1) identification and characterization of collapsible soil sites, (2) estimation of the extent and degree of wetting, (3) estimation of collapse strains and collapse settlements, and (4) selection of design/mitigation alternatives. Estimation of the extent and degree of wetting is the most difficult of these tasks, followed by selection of the best mitigation alternative.  相似文献   

8.
文章通过在某均衡试验场地中的渗透仪上开展土壤水流穿透试验,分析灌溉水对地下水补给方式。试验结果表明:淹灌条件下,粉细砂扰动土中的穿透曲线为典型的单峰对称型,表明粉细砂中的土壤水通过活塞式入渗补给地下水;而亚粘土中的穿透曲线显示多峰、优先穿透、拖尾等现象,表明亚粘土中的土壤水以优势流方式补给地下水。通过对均衡场降水入渗补给的长观资料分析发现:在自然降雨条件下亚粘土中优势流明显,粉细砂中主要以活塞流为主。  相似文献   

9.
针对风沙运动中结皮冲蚀破坏及其寿命问题,通过建立沙粒对结皮的冲蚀模型,采用量纲分析研究风沙运动中单颗沙粒对结皮冲蚀量与沙粒冲击速度、沙粒自旋角速度、沙粒直径、沙粒入射角、结皮硬度等的本构关系,并对结皮冲蚀破坏机理及其寿命预测进行理论研究。数值计算结果表明,沙粒冲击速度、沙粒自旋角速度、沙粒冲击角度、沙粒直径及沙尘暴日数、持续时间都对结皮寿命有明显影响。统计分析各项影响因素的平均值计算表明,在结皮厚度20 mm的情况下,结皮寿命为3～8年,平均寿命5.3年。此研究可以更深刻认识结皮的自然破坏特征,对防沙固沙具有一定的理论意义和实际应用价值。  相似文献   

10.
陶帅  董毅  韦昌富 《岩土力学》2020,41(6):2132-2142
为研究脱湿过程中饱和度改变对土体小应变刚度的影响规律,自主研制了一套非饱和土小应变刚度试验装置。该装置由3部分构成：相对湿度控制系统、变形测试系统和波速测试系统。相对湿度控制系统可分级提供环境室内相对湿度,通过称重模块记录土样质量变化;变形测试系统利用图像采集结合数字图像处理技术获得土样体变;波速测试系统采用压电陶瓷元件制作的波速传感器,可同时测试土样脱湿过程中压缩波及剪切波波速。试验结果表明：该装置能够分级稳定控制相对湿度环境、间接测量土样体积变化及实时测试弹性波波速,进而研究波速表征的小应变刚度随饱和度的变化规律;土样剪切波速及小应变剪切模量随饱和度的降低逐渐增加,压缩波速及小应变体积模量随饱和度的降低先减小后增加。该装置结构简单,便于操作,为研究非饱和土小应变刚度特性提供了科学有效的测试方法与试验手段。  相似文献   

11.
Aeolian (wind) erosion is most common in arid regions. The resulted emission of PM10 (particulate matter that is smaller than 10 μm in diameter) from the soil has many environmental and socioeconomic consequences such as soil degradation and air pollution. Topsoil resistance to aeolian transport highly depends on the surface composition. The study aim was to examine variations in PM10 fluxes in a desert-dust source due to surface composition and topsoil disturbance. Aeolian field experiments using a boundary layer wind tunnel alongside soil composition analysis were integrated in this study. The results show variations in PM10 fluxes (ranging from 9.5 to 524.6 mg m?2 min?1) in the studied area. Higher wind velocity increased significantly the PM10 fluxes in all surface compositions. A short-term natural disturbance caused changes in the aggregate soil distribution (ASD) and increased significantly PM10 emissions. Considering that PM10 contains clays, organic matter, and absorbed elements, the recorded PM10 fluxes are indicative of the potential soil loss and degradation by wind erosion in such resource-limited ecosystems. The findings have implications in modeling dust emission from a source area with complex surfaces.  相似文献   

12.
Water content variations and respective ecosystems of sandy land in China   总被引：1，自引：0，他引：1  
Soil water conservation is essential to the sustainability of sandy farming. In this paper, long-term observation of soil water, dry soil thickness and soil chemical changes are evaluated at eight locations in sandy soil. This paper subdivides the sandy lands and deserts of China into three climate zones: arid (hyperarid and extremely arid), semiarid, and humid (subhumid and subtropical humid), with respect to the bioclimatic zone, aridity, soil water content, and soil chemical characteristics. The water movement conditions, and chemical variations in each zone are analyzed. The paper also estimates the spatial and temporal correlation function of arid soil thickness and soil moisture. Sandy soils organic matter content, CaCO3 content, soluble salts content are investigated. Afforestation and selection of tree species in different sandy areas are suggested to regulate sandy land soil moisture. Sandy land in China can be divided into the four sand stabilization regions according to the shifting sand conditions and the techniques advanced: regions I, II, III, and IV. These results have important implications for remote sensing of soil moisture and soil organic carbon, and soil moisture parameterization in climate models.  相似文献   

13.
孙畅  唐朝生  程青  徐金鉴  张大展 《地球科学》2022,47(10):3701-3722
土体-大气相互作用是指在多种气象要素共同驱动下,地表浅层土体与大气之间进行物质交换与能量传递的复杂过程.受全球气候变化影响,近年来极端气候事件频发.土体的工程性质在日益严峻的气候环境下发生剧烈变化,产生了大量滑坡灾害,给岩土和地质工程领域带来许多新挑战.系统总结了降雨、气温、空气湿度、风以及太阳辐射5个主要气象要素影响边坡稳定性的机制,分析了土体龟裂、地表植被和土体-大气相互作用之间的关联效应.通过介绍各因素在改变边坡稳定性过程中发挥的作用,构建了一个包括气象要素、土体龟裂以及地表植被的土体-大气相互作用分析体系.该体系为今后土体-大气相互作用下土质边坡稳定性研究确定了关键研究问题,所揭示的作用机理可为今后同类研究提供参考.针对该课题的研究现状,笔者提出了今后的研究方向和重点,包括土体-植被-大气相互作用的理论模型、气候作用下冻土坡体失稳机理、极端气候工程地质作用的生态调控措施三个方面.   相似文献   

14.
In temperate regions, eolian deposits of different natures are often pedogenically-altered and mixed with underlying sediments. The research reported in this paper identifies for the first time the presence of eolian deposits in soils of central Tuscany and investigates the characteristics and origin. Five relict, polycyclic paleosol profiles were studied. P1 was situated in a natural dust trap, a doline on top of an isolated limestone hill; P2 and P3 were both situated on a limestone plateau, and P4 and P5 on a mid- and foot slope on schist. The profiles were sampled for routine analyses, iron forms, heavy minerals, major and trace elements, and pollen, spores and non-pollen palynomorphs. Undisturbed samples were taken for micromorphological and SEM analyses. Nine soil horizons were sampled for OSL dating. Eolian deposits were dominant or abundant in the first layers of P1, P2 and P3. OSL age determinations of soil horizons deriving from eolian parent material were middle Holocene. Chemical and heavy mineral analyses indicated different possible sources, including bare slopes, alluvial fans and wide channels, coming from the nearby streams that drain the Middle Tuscany ridge and the Mounts of Chianti; marginal contribution of volcanic ashes was only found in P1.The research demonstrated that wind soil erosion accompanied water erosion and colluvial deposition during the middle Holocene in the Elsa River basin. Pollen spectra, in particular, indicated that soil degradation occurred in an environment showing signs of incipient desertification, resulting from an increase of aridity in a land already strongly influenced by humans. Although central Italy is currently considered to be only marginally affected by wind soil erosion, a climate change, which would imply increased arid conditions, could trigger a new cycle of slope denudation, wind erosion and loess deposition.  相似文献   

15.
Shrubs that exert drag force on the wind significantly affect the air–surface interaction in arid and semiarid regions, and some coastal regions where aeolian processes are active. An understanding of the drag force on wind of shrubs provides important information on the dynamics of shrubs in reducing wind erosion, and their geomorphological significances. Thus, we analyzed the drag force and drag coefficient for model shrubs using wind measurements obtained by particle image velocimetry in a scaled wind tunnel simulation. The drag force was found to be a function of wind velocity and shrub density. Both drag force and drag coefficient revealed a critical shrub density of around 0.08. The vertical drag force changed direction when the shrub density became greater or less than the critical density. The drag coefficient increased rapidly with shrub density when the density was below 0.08, but it increased very gently when the density was increased beyond the critical value. The results have an important theoretical significance for our understanding of the dynamics of vegetated dunes and the windbreak mechanism of shrubs.  相似文献   

16.
全球土壤湿度的记忆性及其气候效应   总被引：7，自引：1，他引：6  
利用1948-2010年全球GPCC月平均降水,GHCN_CAMS月平均气温资料,GLDAS-NOAH月平均、3h土壤湿度和降水资料以及观测资料,分析了土壤湿度与降水和气温之间的关系。结果表明：全球土壤湿度记忆性的时间尺度在20~110d不等,干旱地区浅层（0~10cm）土壤湿度记忆性较短,中深层（10~200cm）较长,湿润区及高山地区土壤湿度记忆性均较长,北半球春季土壤湿度记忆性最长,南半球夏季土壤湿度记忆性最长;降水和气温对同期土壤湿度在不同地区的作用不同,北半球夏、秋季降水是土壤湿度的主要来源,除非洲干旱区以外的中低纬度地区及南半球,土壤湿度随降水的增加而增加,随气温的升高而减小;浅层土壤湿度受同期降水和气温的影响最为显著;前期降水和气温对土壤湿度的影响存在着较大的空间差异,北半球中高纬度地区,当年的夏、秋季降水是次年春季土壤湿度的主要来源,中层土壤（10~100cm）是降水的主要存储层。浅层土壤受外界影响较大,对前期气候信息的存贮有限。中低纬度地区及南半球,中深层土壤更多地是存储前一个季节的气温和降水信息,对跨季节气候信息的存储并不明显;低纬度地区春季土壤湿度的增加可能有利于后期降水的增多,高纬度地区春季土壤湿度的增加可能使后期降水减少,在季节尺度上中层土壤湿度对后期的降水影响较明显,在月至日尺度上浅层土壤湿度对后期降水的影响更重要;春季干旱区尤其是中层土壤湿度的增加可能有利于夏季气温的降低。  相似文献   

17.
在河道中,受水压力和土体本身压力的作用,淤积物的密度增大,物理力学特性发生了很大的变化,如采用公式计算起动流速,则出现较大的偏差.针对实际工程中经常遇到的淤泥质亚粘土的起动流速问题进行了试验研究,研究在特制的矩形管道中进行.通过试验得到了起动临界状态下的摩阻流速,利用天然河道的阻力关系将摩阻流速换算到天然情况,并以河道稳定性为比较目标,与河道水流动力条件进行比较,验证了试验研究结果的合理性和有效性,这为解决河道边界淤积物的起动临界条件问题提供了一种新的思路和方法,因此无论从研究方法上还是解决实际工程问题都具有一定的创新意义.  相似文献   

18.
中国北方土壤风蚀问题研究的进展与趋势   总被引：70，自引：0，他引：70  
土壤风蚀是中国北方土地退化的主要原因之一。国内土壤风蚀的研究工作相对比较薄弱，所取得的进展主要包括区域性的土壤风蚀分布地带性规律和不同时间尺度的准周期性规律，描述性的风蚀强度分级与危害评价，单因子风蚀过程的风洞实验，农田风蚀防治等方面。今后的研究趋势主要表现在土壤风蚀的物理本质、影响因素及发展动态的综合研究，土壤理化性质与表面性质对抗蚀性的影响及其与风蚀的反馈关系，土壤风蚀的基本过程及防治原理，土壤风蚀预报方程与数字模拟，土壤风蚀影响评价模型，土壤风蚀与土地利用以及全球变化的关系，各种观测与实验设备的研究等方面。  相似文献   

19.
Surface evaporation is one of the main processes in the soil–atmosphere interaction. Since it is highly related to meteorological factors and soil properties, determination of evaporation rate from soil surface remains a challenge. To investigate the evaporation from unsaturated soil, a climate control apparatus has been newly developed, which has a feature of completely controlling air temperature, relative humidity and wind speed. Twelve climatic conditions are applied to three kinds of soil specimens to carry out the evaporation tests. The results show that only water content cannot allow an accurate estimation, additional variables accounting for soil texture and wind speed must be included as well. Moreover, a simple approach to parameterize evaporation is presented by the soil moisture θ of top 1-cm layer with considering the effect of soil texture and wind speed. It is found that the new approach is able to accurately estimate the evaporation from unsaturated soil.  相似文献   

20.
Well sorted fine sand pretreated with varying concentrations of two soluble salts (MgCl2 and CaCl2) was tested for threshold shear velocity in a recirculating wind tunnel. These tests demonstrate that even relatively low surface salt concentrations can significantly increase threshold shear velocity. However, the relationships between surface salt concentration and threshold shear velocity for the two salts were not significantly different, which is similar to the results for monovalent chlorides presented by Nickling & Ecclestone. A general relationship between threshold shear velocity and total, surface soluble salt content is presented.  相似文献   

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