|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.|