砾石级沙粒胶结体抗风蚀效益的实验研究

塔克拉玛干沙漠腹地部分垄间地表发育了一种由众多沙粒胶结而成的大颗粒物质,称为沙粒胶结体(sand cemented bodies,缩写为SCB),其直径达到粗沙级、极粗沙级和砾石级。为了研究其对地表风沙活动的影响,本研究以野外采集的砾石级沙粒胶结体(gravel-size sand cemented bodies,缩写为GSSCB)为实验材料,在净风和挟沙风条件下进行了GSSCB覆盖沙面的抗风蚀模拟实验。结果表明:床面的蚀积状态与来流条件、GSSCB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3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,但不同覆盖度范围增加率不同;挟沙风条件下呈蚀积平衡状态时的床面覆盖度临界C_b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C_b值时床面呈风积状态,积沙率与风速的关系较为复杂,80%覆盖度床面积沙率随风速增大呈对数形式增加,但40%覆盖度床面积沙率则随风速增加呈指数形式降低。可见,由于与砾石的物理性质相近,GSSCB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风沙流挟沙颗粒。因此,塔克拉玛干沙漠腹地丘间地天然发育的GSSCB对于地表蚀积过程具有重要影响。GSSCB可作为一种新型固沙技术进行开发。

Wind Tunnel Experiment on the Anti-erosion Benefits of Gravel-size Cemented Bodies from Inter-dune Corridors in the Hinterland of the Taklimakan Desert

There are some larger granular materials whose diameter reach the level of coarse sand, very coarse sand and gravel, naturally distributed on some inter-dune corridors in the hinterland of the Taklimakan Desert. They were made up of a mass of sands which be cemented together by a certain substance, we call them sand cemented bodies (SCB). In order to research the effect of SCB on windblown sand movement, this study investigated the anti-wind erosion ability of the sand surface being covered with gravel-size sand cemented bodies (GSSCB) collected in the field by wind tunnel simulation in net-wind conditions and sand-driving wind conditions respectively. The results indicate that the conditions of erosion-deposition on sand surface depended on the inflow conditions, wind speeds and degrees of GSSCB coverage. All sand beds in all GSSCB 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 degree of GSSCB coverage and wind speed. When the sand beds were in a condition of erosion, the erosion rates decreased exponentially with the increasing degree of GSSCB coverage and increased in forms of different functions with the increasing wind speed. As the coverage rise, the anti-wind erosion rates gradually increased, but the increased ratios were different in different ranges of GSSCB coverage. When the sand bed showed in a condition of erosion-deposition balance under a sand-driving wind condition, its degree of GSSCB coverage reached a critical value C_b in that environment. The value of C_b increased with the increasing speed, whose relationship could be described as a power function. When the coverage was greater than C_b, 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 speed under the sand-driving wind condition. As a result, for the similar physical natures like gravel, the GSSCB coverage does have an anti-erosion benefits for the sand surface, GSSCB can also capture windblown sand from wind-sand flow at a given coverage. So we should pay attention to the effect of GSSCB on the windblown sand movement in the hinterland of the Taklimakan Desert in future aeolian research. A new type of sand fixation technology can be developed soon inspired by GSSCB.