农业土壤抗剪强度的试验研究

对农业土壤的抗剪强度试验研究表明：在土壤含水量一定的情况下，抗剪强度随土壤所承受的垂直压力的增加而线性增大；抗剪强度随含水量的增加而非线性减小。分别确定了土壤抗剪强度与垂直压力、含水量之间的关系，建立了土壤抗剪强度－垂直压力－含水量的数学模型。     

川西地区紫色土抗剪强度水敏性试验研究

土体抗剪强度水敏性是工程稳定性研究与设计的重要参考依据.为了研究含水率对川西地区紫色土抗剪强度的影响规律,并揭示其抗剪强度的水敏特性,在不同主应力下对不同含水率的重塑紫色土进行了室内直剪试验.结果表明:1)抗剪强度具有水敏感性,其强度随含水率增加先增大后减小,并在含水率15％时取得峰值.2)抗剪强度受主应力影响,当主应...     

黄土高原沟壑区坡耕地表层土壤抗剪强度影响因素分析

以淳化坡耕地为研究对象,在人工模拟降雨条件下,设计降雨强度分别为0.5、1.0、1.5、2.0、2.5 mm/min,降雨历时40 min,设计坡度分别为5°、8°、11°、15°、20°,分析了影响黄土高原沟壑区坡耕地表层土壤抗剪强度的3个主要因素:含水量、雨强及坡度.结果表明,降雨结束后,随着表层土壤含水量的降低,抗剪强度会随之增加,相关性较好;雨强对抗剪强度影响不大;坡度较小时抗剪强度会随坡度增加而降低,当坡度增加到15°以上时,随坡度增加抗剪强度随之增加.     

3种植物单根对土体残余抗剪强度影响的研究

课题组采用四联电动直剪仪对3种沙生植物重塑的根-土复合体及素土进行了直接剪切试验,研究其单根对提高土体残余抗剪强度的影响以及不同孔隙水承压条件下根-土复合体的残余抗剪强度变化.结果表明:浅层土压力下3种植物根-土复合体残余抗剪强度均大于素土,且柠条根系固土效果优于沙棘和白沙蒿;不同含水量梯度下,复合体存在最优含水量,该含水量条件下,根-土复合体强度达到最大值;模拟降雨条件下复合体各残余强度指标均大于非降雨条件下的指标,表现为模拟降雨条件下,3种植物复合体残余粘聚力增长率排序为柠条＞白沙蒿＞沙棘,模拟非降雨条件下排序为柠条＞沙棘＞白沙蒿.上述研究定量分析了3种植物根-土复合材料的力学特性,为水土保持树种的选择提供了理论依据,具有一定的应用价值.     

黄河源区高寒草地不同深度土壤理化性质与抗剪强度关系研究

以黄河源区的高寒草地为研究对象,探讨了草地和裸地在0～10 cm、10～20 cm、20～30 cm、30～40 cm和40～50 cm 5种不同深度土壤理化性质和根-土复合体抗剪强度特征.研究结果表明:黄河源区的土壤为弱碱性土,且pH值、密度随着土壤深度增加而增大.土壤含水率、有机质随土壤深度的增加表现出减小的变化趋...     

黄河源区不同退化程度高寒草地理化性质及复合体抗剪强度研究

为研究黄河源区高寒草地退化对土体理化性质及根-土复合体抗剪强度影响,本研究以位于黄河源区青海河南县地区高寒草地为研究对象,通过开展不同退化程度草地野外取样及室内试验,获得土体密度、含水率、颗粒级配、土壤营养元素和植物根-土复合体抗剪强度指标及变化特征.结果表明:(1)在相同退化程度和取样深度下,南旗村试验区土体平均密度...     

增湿条件下兰州Q_3原状黄土的强度特性

采用总应力法,讨论了增湿条件下兰州地区Q3原状黄土应力-应变曲线特征,分析了增湿过程中含水量及围压对极限强度、抗剪强度参数的影响。结果表明:兰州地区Q3原状黄土的强度受含水量变化的影响较大,在低围压时含水量对黄土强度的影响更显著。随着含水量的增大,粘聚力、内摩擦角逐渐减小;粘聚力与含水量之间呈二次多项式关系,内摩擦角与含水量之间呈线性关系。利用摩尔库伦破坏准则得出兰州地区Q3原状黄土增湿条件下极限强度与含水量、围压的计算公式。     

基于环剪试验的黄土滑坡失稳机理研究

黄土滑坡启动变形受到外界因素影响显著,宏观上表现为累积位移-时间曲线呈不同形式增长特征.为了研究不同应力水平下黄土滑坡的剪切变形特性和变形机理,文中开展了不同剪应力条件和不同初始剪应力条件下的非饱和黄土环剪试验.试验结果表明:阶跃型滑坡变形过程中,衰减蠕变阶段的变形量呈现逐渐增加趋势,土体由衰减蠕变形态逐渐过渡到非衰减...     

化学固沙结层的力学强度与抗风蚀能力关系

通过对三种固沙剂的固沙结层的力学强度与抗风蚀能力进行试验对比研究,揭示两者的内在关系,从而为制定化学固沙标准提供依据。实验表明,固沙结层的粘聚力随固沙剂用量增大而增大,并且成直线关系。固沙结层临界侵蚀风速与固沙剂用量呈线性关系,相关性很好;除了粘聚力外,材料的性质对抵抗风沙流的侵蚀也有很大的影响。     

沙柳方格沙障对库布齐沙漠沙丘粒度分布的影响

为定量探讨沙柳方格沙障对沙粒粒度组成与特征的影响,以流动沙丘(LS)、设障2a沙丘(TS)和设障6a沙丘(SS)为研究对象,在沙丘不同部位、不同土层和障格内不同位置进行取样,分析样品的粒度组成与特征。结果表明:1)随着设障年限的增加,粘粒和粉粒含量增加,细砂含量下降,SS粘粒和粉粒含量与TS和LS的含量差异显著,而TS和LS二者间差异不明显;LS、TS各粒级含量在三个层次间差异均不明显,而SS 0-5cm的粘粒、粉粒以及极细砂粒体积含量较其他2层差异显著。2)SS的频率分布曲线变化幅度小于TS和LS的频率分布曲线变化幅度。各沙丘的平均粒径MZ、分选系数δ、偏度SK、峰度KG的大小顺序均表现为SS相似文献   

基于SPH方法的风沙流运动特性研究

文中基于光滑粒子流体动力学(Smoothed Particle Hydrodynamics: SPH)方法,采用五次样条光滑函数,通过调节不同类型粒子光滑因子,对风沙流运动特性进行分析:1)在风沙流起动阶段,沙粒平均水平速度随高度增加而增大,同一高度处沙粒平均水平速度随时间推移而减小.2)风沙流稳定前后,沙粒数均随高度...     

不同粒径沙粒胶结体覆盖对地表风蚀和输沙率抑制效应的风洞模拟

沙粒胶结体(sand cemented bodies,缩写为SCB)是由众多沙粒胶结而成的大颗粒物质,广泛分布于塔克拉玛干沙漠腹地部分垄间地表。通过风洞实验测定了不同风速下不同粒径沙粒胶结体覆盖对沙床面的土壤风蚀率和输沙率变化的影响。结果表明:风速和粒径是影响SCB覆盖沙床面风蚀率的主要因素。在一定的风力条件下,风蚀率随沙粒胶结体粒径的增加呈指数递减变化,在一定的胶结体覆盖度下,风蚀率随风速增加而增大,且粒径越大风蚀率随风速的增加而增大的趋势更为明显;风速不是影响地表输沙率的主要因素,胶结体粒径在一定程度上对输沙率的影响起主导作用。随着胶结体粒径的增加,沙粒在胶结体覆盖床面产生上升过程,且输沙率随粒径的增加而增大,胶结体覆盖对输沙率的抑制作用主要体现在胶结体覆盖的密度效应上,密度越小输沙率越高。即同一盖度下的胶结体颗粒物,大粒径的胶结体较小粒径胶结体沙床面分布密度、数量都相对较小。因此,大粒径胶结体地表输沙率相对较大。不同粒度范围的胶结体覆盖沙床面表现出不同的风蚀和输沙率抑制效应,依次为:2~3 mm3~5 mm5~7 mm7~10 mm10 mm。     

Effects of different types of guardrails on sand transportation of desert highway pavement

Guardrail, an important highway traffic safety facility, is mainly used to prevent vehicles from accidentally driving off the road and to ensure driving safety. Desert highway guardrails hinder the movement of wind-blown sand, resulting in the decline of sand transportation by the pavement and the deposition of sand gains on the pavement, and endangering traffic safety. To reveal the influence of guardrails on sand transportation of desert highway pavement, we tested the flow field and sand tran...     

Influence of salinity and moisture on the threshold shear velocity of saline sand in the Qarhan Desert,Qaidam Basin of China: A wind tunnel experiment

Determination of the threshold shear velocity is essential for predicting sand transport, dust release and desertification. In this study, a wind tunnel experiment was conducted to evaluate the influence of salinity and moisture on the threshold shear velocity of saline sand. Saline sand samples (mean particle size of 164.50-186.08 μm and the total silt, clay and salt content of 0.80%-8.25%) were collected from three saline sand dunes (one barchan dune and two linear dunes) in the Qarhan Desert, Qaidam Basin of China. Original saline sand samples were placed in two experimental trays for wet and dry processing to simulate deliquescence and desiccation, respectively. Surface moisture content ranging from 0.30% to 1.90% was generated by the steam method so that the saline sand can absorb water in a saturated water vapor environment. The motion of sand particles was determined by the observers with a solid laser. The laser sheet (0.80 cm thick), which was emitted by the solid laser, horizontally covered the sand surface and was bound to the sand. Results show that the cohesion of saline sand results from a combination of salt and water. The threshold shear velocity increases exponentially with the increase in crust thickness for the linear sand dunes. There is a positive linear correlation between the original moisture content and relative threshold shear velocity. The threshold shear velocity of dewatered sand is greater than that of wet sand with the same original moisture content. Our results will provide valuable information about the sand transport of highly saline soil in the desert.     

雅鲁藏布江河谷沙丘沉积物粒度特征及其环境指示

雅鲁藏布江(雅江)河谷是青藏高原南部风成沉积物的典型分布区。通过对雅江河谷的沙丘表层沉积物进行系统采样,分析了沉积物粒度特征及其空间分异规律,以期揭示河谷风沙沉积环境。结果表明:1)沙丘沉积物粒度以细砂和中砂组分为主,其次为极细砂、黏土-中粉砂、粗砂和粗粉砂组分。分选较差至中等,偏度为正偏至极正偏,峰态介于正态至很尖锐。2)沙丘沉积物粒度组成及参数在流域尺度上并无统一的空间变化规律,但在雅江上游和中游存在明显区域差异。风沙过程是造成这种区域变化的主要原因,水沙过程并不是影响雅江河谷沙丘粒度变化的主要原因。3)雅江河谷沙丘沉积物具有相似的搬运方式和沉积环境,主要由跃移质和蠕移质组成,悬移组分含量低,沉积环境主要为河流沉积和湖泊沉积,共同指示河岸和河漫滩沉积物是雅江风成沙丘的主要物质来源。     

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.     

Influences of sand cover on erosion processes of loess slopes based on rainfall simulation experiments

Aeolian-fluvial interplay erosion regions are subject to intense soil erosion and are of particular concern in loess areas of northwestern China.Understanding the composition,distribution,and transport processes of eroded sediments in these regions is of considerable scientific significance for controlling soil erosion.In this study,based on laboratory rainfall simulation experiments,we analyzed rainfall-induced erosion processes on sand-covered loess slopes(SS)with different sand cover patterns(including length and thickness)and uncovered loess slopes(LS)to investigate the influences of sand cover on erosion processes of loess slopes in case regions of aeolian-fluvial erosion.The grain-size curves of eroded sediments were fitted using the Weibull function.Compositions of eroded sediments under different sand cover patterns and rainfall intensities were analyzed to explore sediment transport modes of SS.The influences of sand cover amount and pattern on erosion processes of loess slopes were also discussed.The results show that sand cover on loess slopes influences the proportion of loess erosion and that the compositions of eroded sediments vary between SS and LS.Sand cover on loess slopes transforms silt erosion into sand erosion by reducing splash erosion and changing the rainfall-induced erosion processes.The percentage of eroded sand from SS in the early stage of runoff and sediment generation is always higher than that in the late stage.Sand cover on loess slopes aggravates loess erosion,not only by adding sand as additional eroded sediments but also by increasing the amount of eroded loess,compared with the loess slopes without sand cover.The influence of sand cover pattern on runoff yield and the amount of eroded sediments is larger than that of sand cover amount.Furthermore,given the same sand cover pattern,a thicker sand cover could increase sand erosion while a thinner sand cover could aggravate loess erosion.This difference explains the existence of intense erosion on slopes that are thinly covered with sand in regions where aeolian erosion and fluvial erosion interact.     

Fetch effect on the developmental process of aeolian sand transport in a wind tunnel

As the sand mass flux increases from zero at the leading edge of a saltating surface to the equilibrium mass flux at the critical fetch length, the wind flow is modified and then the relative contribution of aerodynamic and bombardment entrainment is changed. In the end the velocity, trajectory and mass flux profile will vary simultaneously. But how the transportation of different sand size groups varies with fetch distance is still unclear. Wind tunnel experiments were conducted to investigate the fetch effect on mass flux and its distribution with height of the total sand and each size group in transportation. The mass flux was measured at six fetch length locations(0.5, 1.2, 1.9, 2.6, 3.4 and 4.1 m) and at three free-stream wind velocities(8.8, 12.2 and 14.5 m/s). The results reveal that the total mass flux and the mass flux of each size group with height can be expressed by q=aexp(–bh), where q is the sand mass flux at height h, and a and b are regression coefficients. The coefficient b represents the relative decay rate. Both the relative decay rates of total mass flux and each size group are independent of fetch length after a quick decay over a short fetch. This is much shorter than that of mass flux. The equilibrium of the relative decay rate cannot be regarded as an equilibrium mass flux profile for aeolian sand transport. The mass fluxes of 176.0, 209.3 and 148.0 μm size groups increase more quickly than that of other size groups, which indicates strong size-selection of grains exists along the fetch length. The maximal size group in mass flux(176.0 μm) is smaller than the maximal size group of the bed grains(209.3 μm). The relative contribution of each size group to the total mass flux is not monotonically decreasing with grain size due to the lift-off of some small grains being reduced due to the protection by large grains. The results indicate that there are complex interactions among different size groups in the developmental process of aeolian sand transport and more attention should be focused on the fetch effect because it has different influences on the total mass flux, the mass flux profile and its relative decay rate.