泥石流梁式格栅坝拦砂性能试验研究

通过特殊泥石流试验装置 ,对泥石流梁式格栅坝拦砂性能进行研究 ,初步得到 :梁式格栅坝有全部闭塞、临时闭塞、半闭塞、未闭塞 4种闭塞类型。当梁间距 b与泥石流体中最大颗粒粒径 dm ax之比 b/ dmax≤ 1.0时 ,格栅坝基本闭塞 ;b/ dmax≥ 1.5时 ,格栅坝未闭塞 ;1.0 相似文献   

泥石流缝隙坝对龙头泥砂体积浓度变化影响试验研究

(1)通过前人研究成果及野外调查和预备试验.对泥石流龙头泥砂体积浓度变化影响因子进行分析,写出了其无因次关系式,并根据试验结果,建立了泥石流缝隙坝泥砂体积浓度比的多元回归关系式;(2)试验发现:在相同的水槽坡度和泥砂粒径组成的条件下,泥石流过坝前后的泥砂体积浓度比会受到切口密度、相对切口宽度和相对切口深度的影响,均呈现正相关的关系.     

梳子坝切口深度对淤砂形态影响的试验研究

通过室内水槽试验，探讨梳子坝切口深度对淤砂形态的影响等，初步分析得到以下几点结论：（1）在全闭塞状态下，坝址附近淤砂高度大致等于坝高，并不受切口深度的影响；在部分闭塞状态下，坝址附近淤砂高度受切口深度的影响非常明显，并有随切口深度的增大而降低的趋势；在不闭塞状态下，坝址附近淤砂高度等于切口深度，是坝前泥砂淤砂的基准点。（2）切口深度影响淤砂长度，随着切口深度的降低，淤砂长度有逐渐减小的趋势。（3）在淤砂形态上，三种切口闭塞状态下都有一个共同的特征：在淤砂区的尾部，有一个陡坡，但陡坡的起点有随切口深度的减小而逐渐后退的趋势。（4）在淤砂形态上，部分闭塞和不闭塞两种状态下还有一个共同的特征：在淤砂区的前端，都有一个缓坡。但部分闭塞时缓坡坡顶（淤砂肩）位置大致相近；但不闭塞时缓坡坡顶（淤砂肩）的位置有随切口深度的减小而变得距离坝址更近的趋势。     

透水型防沙坝拦截裹挟树木泥石流的性能

在泥石流易发区的小流域沟壑治理中,设计修建透水型防沙坝,快速形成堵截的功能。而拦截功能,主要取决于透水断面建材的净间距(L)和泥石流中石砾的最大粒径(dmax)之比,建议设计参数取1.0≤L/dmax≤1.5。在发生泥石流时,当大量的树木常裹挟于泥石流中,难以忽略流动树木对拦截功能的影响。2009年日本学者进行了透水型防沙坝拦截裹挟树木的泥石流试验。其研究结论是:泥石流拦截率的提高,与LV/dmax密切相关。木材堆积率在10%以下,拦截率表现离散。伴随LV/dmax的增大,其离散度有变大的趋势,木材堆积率的拦截率影响变大。此项研究对于我国研究防御同类泥石流,具有借鉴作用。     

钢制格栅坝拦截泥石流效果试验研究

为拦截泥石流,世界各地设计并实施了多种坝型。在日本,多采用透过型格栅坝来防治泥石流危害。2005年日本学者中村?等人开始研制混合类加前扶垛型钢制开放式格栅坝。其结构做了调整,在原独立单体的基础上,增设横栏、加密立柱,构成桁架式格栅坝,研究其对泥石流的拦截效果。试验结果表明:在格栅坝上游侧有巨砾石堆积,在格栅坝内部没有堵塞。如果横栏的间隔是d95×1.0以下,与开口间隔没有关系,堵塞率在95%以上。对于不同类型的泥石流,如果横栏间隔在b2/d95=1.0,最下层横栏的间隔(b1/d95=1.0,1.25,1.5)没有关系。开口在b3/d95=1.5得到相同的泥石流拦截率。横栏间隔为b2/d95=1.0的格栅坝上层部分,没有堵塞,泥沙的拦截率急剧减少。辅助纵筋配置要求,可采用较细线材,纵筋的间隔必须紧密,才能对泥石流有拦截率。在泥石流多发地区,设置格栅坝,辅助纵筋的间隔设置为b1/d80=0.5,1.0,对泥沙拦截十分有效。     

关于上部狭窄式格栅坝的研究

在泥石流易发区,设置格栅坝,以期达到阻止泥石流的流动或起到消能的作用。以往的实践证明,同规格格栅坝拦截泥石流效果不十分理想。因此,在试验的基础上,研究了泥石流粒径、质量分数变化的特点,通过同规格及上部窄格模型坝拦截泥石流的模拟过流试验,分析7种格栅尺寸的坝型拦截泥石流的效果,得出如下结论：同规格及上部窄格格栅坝均能有效地拦截泥石流的龙头;泥砂量减少率随着上部的Linin／d95值的增大而减小,当Lmin/d95＜1．6时,减少率达到80％以上;且随着下部格栅间隔的增大而减小。因此,在具体设计时,应采用上部窄格的格栅坝型,下部格栅尺寸在考虑Lmin/d95的基础上,同时还应考虑Lmax／d95的比值。     

小麦秸秆覆盖量对坡面流水动力学特性影响

为系统研究小麦秸秆覆盖量对坡面流水动力学特性的影响,采用室内定床模拟试验,探究在不同流量(3.0、4.5、6.0、7.5、9.0 L/min)和坡度(3°、5°、10°、15°)下,坡面流水动力参数随秸秆覆盖量(0、1.5、2.5、3.5、4.5 t/hm²)的变化特征。结果表明：1)秸秆覆盖显著影响坡面流流型,在不同流量和坡度下,无秸秆覆盖时坡面流型均为急流,而在秸秆覆盖条件下,坡面流型均变为缓流。当流量≤7.5 L/min时,流态均为层流,当流量>7.5 L/min时,流态均为过渡流。2)随着秸秆覆盖量的增加,坡面流流速分别较裸坡降低了47.85%、53.86%、57.69%、60.11%。3)不同覆盖量下,坡面流流态指数随坡度的变化规律不一致。覆盖量≤2.5t/hm²时,随坡度的增加,流态指数呈先增后减的变化趋势,覆盖量>2.5 t/hm²时,流态指数随坡度的增加而逐渐减小。4)不同覆盖量下,坡面流阻力系数随坡度的变化规律不一致。秸秆覆盖坡面阻力系数是裸坡的9.36～19.68倍。低覆盖量下(≤2.5t...     

径流深和侵蚀量与集水面积、坡度及降雨量关系研究

[目的]分析径流深、侵蚀量与集水面积、坡度等影响因子间定量关系,为土壤侵蚀物理模型构建及参数率定提供参考。[方法]基于不同下垫面措施野外径流小区天然降雨实测资料,构建了年降雨径流深、侵蚀量多参数非线性估算模型。[结果]降雨产流阈值随集水面积、坡度呈先减后增、先增后减的变化趋势。年径流深(Y₁)和年土壤流失量(Y₂)随面积呈先增后减变化趋势;Y₁随坡度呈先减小后迅速增加变化趋势,Y₂随坡度呈持续递增变化规律;Y₁和Y₂随年降雨量持续增加。当坡面面积为130 m²时,Y₁和Y₂均达最大值;当坡度为13.5°时,Y₁达最小值。Y₁多参数非线性回归估算模型精度较好,70%数据点相对误差分布在±30%内。[结论]集水面积、坡度和年降雨量三者交互作用对年降雨径流深和侵蚀量影响作用最大;对于年降雨径流深和侵蚀量而言,均存在临界集水面积和临界坡度值。     

利用铁丝网坝拦截滑坡体的试验研究

防治泥沙灾害,以往多采取被动式挡土墙。1971～2011年日本学者千叶干等人研究弹性挡土墙—利用铁丝网坝拦截滑坡。在实际坡面的底端设置铁丝网坝,重复数次拦截泥沙,最终铁丝网坝没有破坏。应用高频照相机摄影解读出泥沙滑动速度为11 m/s。能拦截来自高为5～100 m,坡度为30°～60°坡面上最大粒径为60 mm的泥沙。实践证明铁丝网坝具有拦截滑坡泥沙的功能。     

关于格型坝最大输砂量减少率的研究

<正>1 试材本试验用的砂石为平均粒径4.98mm,最大粒径9.56mm(95%粒径为8.80mm)的混合砂石,且容重为2.61g/cm~3,内摩擦角为42°。分别准备了由纵梁净距L~v与横梁净距Lh组成的23.5mm×23.5mm,23.5mm×17.0mm,17.0mm×23.5mm,17.0mm×17.Omm,23.5mm×12.7mm,12.7mm×23.7mm6种坝模型。以下所示的试验结果图均用与d_95之比表示。用于试验的水槽宽15.3cm,长4m,侧壁为丙烯基制品,水槽底为木制品。水槽坡度分10°,15°,20°三种,且对应的供水量分别为土1.0l/s,1.5l/s,2.0l/s。     

Changes in penetration resistance of Ultisols from southern China as affected by shearing

Shear stresses and soil properties modified due to stress play an important role during formation of seals in a series of rainfall events and during tillage. The objectives of the study were to evaluate the effects of the penetrometer geometry on the penetration resistance as affected by shearing under different initial soil conditions and to use the information on soil strength to elucidate shearing process. Nine homogenous air-dried soils (<2 mm) were sprayed and stored so as to obtain equilibrium soil water contents. The moist soils were sheared by horizontal displacement of layers of soil particles/aggregates in between hands in one direction. The soil cores were prepared with comparable bulk density before the measurement of maximum penetration resistance (P_max) with a small flat tip and a cone tip penetrometers. At a wide range from 0.05 to 6.2 MPa, P_max was linearly correlated between the small flat tip and the cone tip penetrometers. The conversion ratio was higher under the saturation condition irrespective of the shearing effect. The penetrometer with the small flat tip was more sensitive for the weak soils. Shearing generally increased P_max in most cases, but it decreased P_max for some sandy soils under both saturated and unsaturated conditions and for a clayey soil under the saturated condition. The soil consisting of swelling clay exerted a decrease in P_max. Rearrangement and/or sliding of particles/aggregates and increase in soil suction during shearing were attributed to the increase in P_max. Increase in porosity due to the aggregation during shearing was ascribed to the decrease in P_max. In addition, it was shown that agricultural cultivation resulted in a reduction in soil strength.     

梳子坝对土石流之防治效率

梳子坝是一种透过性坝体，可以有效地防止土石流之危害。因此，本研究经由土石流过梳子坝的质量守恒定律和渠槽试验，分别建立土砂流出率、泥砂体积浓度比及贮砂率等三种主要的效率参数，作为评估梳子坝防治土石流之效率，并据以发展出一种简单的设计模式，可以用来设计单一的梳子坝的高度、开口间距及总开口宽度等坝体几何因子。     

河龙区间坝库参数与减沙效益关系研究

对黄河中游河龙区间晋西北片、陕北片坝库控制面积占比、坝库单位面积库容等参数与水利水土保持措施减沙效益关系进行了研究，结果表明：（1）晋西北片若没有坝库工程，仅靠水土保持坡面治理措施只能取得14％的减沙效益；每增加100km^2的坝库控制面积，即可提高2％的减沙效益；每增加400万m^2的库容，即可提高1％的减沙效益;坝库单位面积库容每提高1万m^2／km^2，减沙效益即可提高约10％。（2）陕北片减沙效益主要由坝库工程产生。减沙效益提高10％，坝库单位面积库容需要提高5万m^2／km^2。要使流域水土保持综合治理减沙效益达到20％以上，坝库单位面积库容应在6万m^2／km^2以上。（3）在黄河中游多沙粗沙区，要实现40％左右的减沙效益，坝库单位面积库容应达到167／m^2／km^2以上。     

复合式出流口滞洪坝之滞洪特性研究

山坡地滞洪设施中,不同出流口形式之滞洪坝,有不同的滞洪效应及滞洪容积。为剖析滞洪设施中受制入流历线作用下其滞洪容积变化,以无因次滞洪理论为基础,讨论滞洪池内其滞洪容积对应时间变化情形,进而推求该滞洪池之最小滞洪容积;同时采用下方宽底梯形断面,上方衔接一窄口矩形之复合式出流口滞洪坝进行室内渠槽试验;并制造不同形态之入流历线,针对不同梯形底宽布置下之滞洪效应及出流口流量公式分析探讨。证明复合式出流口于低流量时,因宽底梯形断面可将水快速排出,增加池内净空间;当流量大时可增加其滞洪能力。故本复合式出流口设计,于入流条件相同下,其所需之最小滞洪容积较矩形窄口式为小。     

Soils as carbon sinks: the global context

Abstract. Soil carbon sequestration could meet at most about one-third of the current yearly increase in atmospheric CO₂-carbon, but the duration of the effect would be limited, with significant impacts lasting only 20–50 years. Coupled with this limited duration, increases in population and per-capita energy demand mean that soil carbon sequestration could play only a minor role in closing the difference between predicted and target carbon emissions by 2100. However, if atmospheric CO₂ concentrations are to be stabilized at reasonable levels (450–650 ppm), drastic reductions in carbon emissions will be required over the next 20–30 years. Given this, carbon sequestration should form a central role in any portfolio of measures to reduce atmospheric CO₂ concentrations over this crucial period, while new energy technologies are developed and implemented. International agreements, such as the Kyoto Protocol, encourage soil carbon sequestration and could be used to formulate soil carbon sequestration polices. Such policies need to take account of other environmental impacts as well as political, economic and societal needs, so that they form part of a raft of measures encouraging sustainable development. Of the carbon sequestration options available, those of a 'win–win' nature, that is, those that increase carbon stocks at the same time as improving other aspects of the environment, and those that protect or enhance existing stocks ('no regrets' implementation) show the greatest promise in meeting these goals.     

跌水坝可实现沟壑的快速治理

在沟壑治理工程布置过程中,存在着单纯拦截、贮蓄的现象,缺乏完全理论研究与指导。甚至水土保持技术文件也存在片面性,导致基层实施单位“年年筑坝年年垮、数量升级无实存”。根据伯努里能量守恒定律,工程布设应分为抬高侵蚀基点Z₂与降低侵蚀源点Z₁两种途径。为此引进跌水坝概念。提出在沟壑治理中,不可片面强调“抬或降”,应将抬高侵蚀基点与降低侵蚀源点有机配合,科学地将沟道分割成若干的水力平衡断面,上有跌水坝控制下切护床底,下有谷坊坝拦蓄水土可造田。这样,沟壑治理必然收到事半功     

Indicator of potential residual carbon in soils after exogenous organic matter application

An indicator to evaluate the proportion of exogenous organic matter (EOM) remaining in soils over the long-term after application has been developed. A database was constructed with analytical data corresponding to 83 EOMs, including sludges, composts, animal wastes, mulches, plant materials and fertilizers. The data included results of proximal analysis (soluble, SOL, hemicellulose-, HEM, cellulose-, CEL, and lignin-like, LIC, fractions, in g kg⁻¹ total organic matter) and of carbon (C) mineralization during long-term incubations under laboratory conditions (in g kg⁻¹ exogenous organic C, EOC). The potential residual organic C after EOM application to soil was assessed from the extrapolation of the incubation results. Then, partial least square regression was used to relate EOM characteristics to the proportion of potentially residual organic C previously determined from the incubations. The biochemical fractions of EOM were not predictive enough to develop the indicator. The proportion of organic C mineralized during 3 days of incubation (C_3d) was cumulated and appeared to be the most predictive variable of residual organic C. The proposed indicator of residual organic carbon in soils (expressed as g EOC kg⁻¹) was I_ROC = 445 + 0.5 SOL – 0.2 CEL + 0.7 LIC – 2.3 C_3d. The indicator was calculated for the main types of EOM applied to soils. When compared with the few field data of residual C measured in long-term field experiments, the values provided by the indicator seemed to be over-estimated (i.e. EOC degradation could be faster under field conditions than during laboratory incubations).     

Heat pipe phenomenon in soil under reduced air pressure

We measured the heat flux, temperature distribution and water content of an unsaturated Ando soil under a constant temperature gradient and reduced air pressure to investigate the mechanism of latent heat transfer in the soil and its relationship to the distribution and circulation of soil water. As the air pressure decreased, the heat flux increased for the soil samples with an initial volumetric water content ( θ _ini) greater than 0.30 m³ m⁻³, but did not change for θ _ini less than 0.20. While the temperature gradient of the sample did not change for θ _ini greater than 0.30 m³ m⁻³, it did increase on the hotter side of the sample and decreased on the colder side for θ _ini less than 0.20. The water content did not change, and a homogeneous distribution of water content was observed for θ _ini greater than 0.30 m³ m⁻³. For θ _ini less than 0.20, the water content decreased on the hotter side and increased on the colder side, forming a large water content gradient. The large transfer of latent heat was caused by the circulation of water vapour and liquid water, which resulted in the homogeneous water distribution. We concluded that the soil functions as a heat pipe through a series of micro-heat pipes centred on the soil pores. Our experimental results will help to explain the transfer mechanism of latent heat in soil as a heat pipe phenomenon.     

锥-板环形水槽的研制及其在颗粒起动试验中的应用

在颗粒起动观测试验中,传统长直型水槽及环形水槽试验无法观测流体长期作用下的颗粒运动,依据锥-板转子流变仪原理,设计了一种锥-板环形水槽装置;采用无量纲拖曳力作为起动时的流体力学指标,结合CCD(电荷耦合组件,charge coupled device)成像技术及PIV(粒子图像测速,particle image velocimetry)技术,运用该装置对层流时无黏性均匀颗粒在流体长期作用下的运动形态及起动规律进行了观测,观测发现流体长期作用下颗粒的起动为连续的起动过程,存在2个不同的临界状态,分别为初始临界状态和饱和临界状态,初始临界状态下的起动拖曳力和经典Shields曲线的取值基本一致,饱和临界状态下的起动拖曳力明显高于Shields曲线的取值,表明锥-板环形水槽是一种合理有效的颗粒起动观测装置,特别适用于流体长期作用下的颗粒起动规律研究。