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流沙地砾级沙粒胶结体基本特征及抗风蚀效益的风洞模拟
孙娜
学位类型硕士
导师徐新文
2015
学位授予单位中国科学院大学
学位授予地点北京
学位专业环境工程
关键词砾石级沙粒胶结体 风蚀率 抗风蚀效率 风沙流结构
摘要在塔克拉玛干沙漠腹地的部分垄间平沙地中,天然分布有一种特殊物质——砾石级沙粒胶结体(gravel-size sand cemented bodies,缩写为GSSCD)。本文以GSSCD为材料,进行了实验研究,主要结论如下: (1)其与地表的粗砂和极粗砂呈复区分布,共同构成了覆盖沙面的大颗粒层。实地调查和取样分析表明,砂粒胶结体直径大小不一,能达到粗砂级、极粗砂级和砾石级(细粒和中砾),最大可达23.5 mm;颗粒形状不规则,质地较硬,手捏不碎;比重为2.51g/cm3,略小于砾石和当地沙丘砂;可溶物的pH值呈中性,电导率2.56 ms/cm,主要成分为CaSO4。砾石尺度的砂粒胶结体在地表的分布密度可达807粒/m2,覆盖度2~3%,组成砂砾胶合体的沙粒物质主要以细沙(125-250μm)和极细沙(63-125μm)为主。 (2)在净风和挟沙风条件下进行了GSSCD覆盖沙面的抗风蚀模拟实验。实验结果表明:床面的蚀积状态与来流条件、覆盖度和风速均有关,净风时所有覆盖度床面均呈风蚀状态,挟沙风时随覆盖度和风速而变化,床面可呈三种状态:风蚀、蚀积平衡、风积;在风蚀状态时,床面风蚀率随覆盖度增大以指数形式降低,随风速增大而以多种函数形式增加,抗风蚀效率随覆盖度增大而逐渐增加,但不同覆盖度范围内增加率不同;挟沙风条件下呈蚀积平衡状态的床面覆盖度临界Cb值与风速大小有关,随风速增加呈幂函数形式增加;在挟沙风条件下,覆盖度大于Cb值时呈风积状态,床面风积率与风速的关系较为复杂,80%覆盖度床面风积率随风速增大呈对数形式增加,但40%覆盖度床面风积率则随风速增加呈指数形式降低。GSSCD覆盖确实具有与砾石相类似的抗风蚀效益,并且在一定覆盖度条件下还能捕获流沙颗粒。因此,塔克拉玛干沙漠腹地丘间地天然发育的GSSCD对于地表蚀积过程具有重要的影响。 (3)净风下,风速不变,随着覆盖度从2%增加到80%,输沙率递减;覆盖度相同时,随着风速的增大,输沙率增加。三种风速下各不同覆盖度时,λ的值几乎均大于1,表明沙面基本处于吹蚀状态。12m/s风速下的λ值均明显高于8和10m/s时,随着风速的增加,λ增加,即风速越高,砾石级沙粒胶结体床面沙粒的吹蚀越强烈。 (4)挟沙风下,覆盖度从2%-80%,各风速下没有出现 “象鼻”效应,风沙流结构并未发生变异,输沙率的变化基本遵循指数衰减规律。风速8m/s时,不同的覆盖度下λ值在0.8-1.4范围内,床面的沙粒存在风蚀,风积和平衡三种过程。风速10m/s和12m/s时,λ值均大于1,即在较高风速下,沙面在沙源充分时有利于风蚀。10m/s时,λ值在1.5-2.3之间,12m/s风速时,λ值在2.0-3.1之间,可见随风速增加,λ值有一种增大的趋势,即风速越高,沙粒吹蚀的过程越明显。
其他摘要There are some larger granular materials whose diameter reach the level of coarse sand, very coarse sand and gravel, naturally distribute on some inter-dune corridors in central Taklimakan Desert. Due to they were made up of a mass of sand which be cemented together by a certain substance, we call them gravel-size sand cemented bodies (GSSCD). The GSSCD is taken as experimental materials in this study. The primary conclusions were as follows: (1)They formed a special large granular layer covering the sand surface together with coarse sand and very coarse sand. Field investigation and sampling analysis indicated that the grain diameter of sand cemented body was uniform, the size could reach the level of coarse sand, very coarse sand and gravel. The diameter of larger ones was more than 10 mm, and the diameter of maximal one was up to 23.5 mm. The shapes of sand cemented bodies were very diverse and irregular. It was very hard and even not scattered with water soak. Its specific gravity was about 2.51g/cm3, less than gravel and local dune sand. The salt content of sand cemented body was so high that its electrical conductivity couldreach 2.56 ms/cm just like heavy saline soil. Its ingredients in its water extract of crushed material were dominated by calcium sulphate. It was in neutral conditions with pH value of 7.40.The gravel-size sand cemented body lies on the sand surface with a density of 807 particles per a square meter and its coverage could reach 2 to 3 percent. The primary substance of GSSCD was fine sand and very fine sand. (2)This study investigated the anti-wind erosion ability of the sand surface being covered with gravel-size sand cemented bodies (GSSCD) collected in the field under by wind tunnel simulation in net-wind conditions and sand-driving wind conditions respectively. The results indicated that the conditions of erosion-deposition on sand surface were depended on the inflow conditions, wind speeds and degrees of GSSCD coverage. All sand beds in all GSSCD coverage treatments showed an erosion status under net-wind condition. But there were three conditions of erosion, erosion-deposition balance and deposition under sand-driving wind conditions, the conditions varied with the degrees of GSSCD coverage and wind speeds. When the sand beds were in a condition of erosion, the erosion rates decreased exponentially with the increasing degrees of GSSCD coverage and increased in forms of different functions with the increasing wind speeds. As the coverage rised, the anti-wind erosion rates gradually increased, but the increased ratios were different in different ranges of GSSCD coverage. When the sand bed showed in a condition of erosion-deposition balance under a sand-driving wind condition, its degree of GSSCD coverage reached a critical value Cb in that environment. The value of Cb increased with the increasing speeds, whose relationship could be described as a power function. When the coverage was greater than Cb, the sand bed showed a sand deposition status. However, the relation between the sand deposition rates and wind speeds was complex. The sand deposition rates increased as a logarithm function at the coverage of 80% and decreased as an exponent form at the coverage of 40% with the raising wind speeds under the sand-driving wind condition. (3)Net-wind, the transport rate decreased with the increasing coverage (from 2% to 80%) under the same wind speed. Under the same coverage, the transport rate increased with the increasing wind speed. The λ values were almost greater than 1 under different coverage and wind speed. It indicated that the sand surface basically stayed at erosion state. The value of λ increased with the increasing of wind speed, λ at 12m / s wind speeds were significantly higher than that at 8 and 10m / s wind speeds. And that is, the higher the wind speed, the more intense the sand bed erosion. (4)Sand-driving wind, as the coverage raise from 2% to 80%, no "trunk" effect and changed sand flux structure were observed. The sand transport rate basically followed the exponential decay. The range of λ was from 0.8 to 1.4 under 8m/s wind speed, indicated that the sand bed showed three states including erosion, aeolian and balance. The value of λ is higher than 1 on 10m/s (1.5-2.3) and 12m/s (2.0-3.1) wind speeds. It was seemed that the value of λ was increaseing with the wind. The higher of the wind speed, the more obvious sand erosion could be observed.
学科领域环境工程
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14666
专题研究系统_荒漠环境研究室
作者单位中科院新疆生态与地理研究所
推荐引用方式
GB/T 7714
孙娜. 流沙地砾级沙粒胶结体基本特征及抗风蚀效益的风洞模拟[D]. 北京. 中国科学院大学,2015.
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