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61.
Clayey sand can be considered as a composite matrix of coarse and fine grains. The interaction between coarser and finer grain matrices affects the overall stress–strain behavior of these soils. Intergranular void ratio, es (which is the void ratio of the coarser grain matrix) can be utilized as an alternative parameter to express the compressive response of such soils. Oedometer tests conducted on reconstituted kaolinite–sand mixtures indicate that initial conditions, percentage of fines, and stress conditions influence the compression characteristics evidently. Tests showed that, up to a fraction of fines, which is named as transition fines content (FCt), compression behavior of the mixtures is mainly controlled by the sand grains. When concentration of fines exceeds FCt, kaolinite controls the compression. It was found that FCt varies between 19% and 34% depending on the above mentioned factors. This range of fines content is also consistent with various values reported in literature regarding the strength alteration. Performed direct shear tests revealed that there is also a close relationship between transition fines content and shear strength, which is harmonic with the oedometer test results. 相似文献
62.
甘肃河西走廊沙尘暴与赤道中,东太平洋海温之间的遥相关分析 总被引:34,自引:14,他引:20
春、夏季甘肃河西走廊沙尘暴发生次数与赤道中、东太平洋海温之间遥相关分析结果表明:春、夏季河西走廊沙尘暴发生次数与前二年赤道中、东太平洋海温的负相关最好,时间过远或过近,相关性反而较差。利用前期的赤道中、东太平洋海温可以较好地预报出河西走廊春季沙尘暴发生的多寡。 相似文献
63.
塔克拉玛干沙漠石油公路沿线风沙活动的气候环境 总被引:5,自引:2,他引:3
塔克拉玛干沙漠石油公路沿线风沙活动是由塔木盆地内热能释放与冷空气入侵相互作用的结果。冷期,盆地内冷高压逆温作用较强,地面热能不足,使得风力和风沙活动强度弱;暖期,盆地内热源剧增,每当热能源饱和遇到冷空气入侵诱导,导致了强风及强风沙活动天气。可见,区内风沙活动及风成景观的塑造过程,主要是在暖干期进行的。 相似文献
64.
This paper examines present and future resource utilization in the tidal section of the Georges River in the southern part of Sydney. Over the last 30 years, the physical characteristics of the river have changed as a result of urbanization, changed hydrologic regime and sand dredging. Urbanization has resulted in an increase in population from 190,000 in 1947 to 550,000. This has resulted in an increase in runoff, sediment input to the river and waste disposal. The change in hydrologic regime has resulted in a substantial increase in the magnitude and frequency of flooding which has increased erosion. Sand dredging has increased the channel capacity, enlarged the tidal prism and increased water turbidity. It has also resulted in extensive bank erosion in the upper part of the river and extensive deposition lower down as tailings are deposited. Although most of these changes have resulted in the deterioration of environmental quality, use of the river for recreation and as an urban amenity has increased. 相似文献
65.
The paper presents a comprehensive study of the failure envelope (or capacity diagram) of a single elastic pile in sand. The behavior of a pile subjected to different load combinations is simulated using a large number of finite element numerical calculations. The sand is modeled using a constitutive law based on hypoplasticity. In order to find the failure envelope in the three-dimensional space (i.e. horizontal force H, bending moment M and vertical force V), the radial displacement method and swipe tests are numerically performed. It is found that with increasing vertical load the horizontal bearing capacity of the pile decreases. Furthermore, the presence of bending moment on the pile head significantly influences the horizontal bearing capacity and the capacity diagram in the H–M plane manifests an inclined elliptical shape. An analytical equation providing good agreement with the 3D numerical results is finally proposed. The formula is useful for design purposes and the development of simplified modeling numerical strategies such as macro-element. 相似文献
66.
在野外考察的基础上,选择13个典型样地,研究了巴丹吉林沙漠南缘植被组成、群落特征和植被格局。结果表明:调查的样地中有荒漠植物31种,其中灌木12种,多年生草本11种,一二年生草本8种。种群密度3 000—14 000株·hm-2,优势种在群落中地位显著,群落稳定性较差;植被斑块面积小、最大斑块指数低。沙漠南缘年降水量虽然仅100 mm左右,但有霸王(Zygophyllum xanthoxylon)、红砂(Reaumuria soongarica)和沙蒿(Artemisia desertorum)等灌木和半灌木天然植物群落分布,有白刺(Nitraria tangutorum)和膜果麻黄(Ephedra przewalskii)灌丛沙堆,沙丘上生长着沙拐枣(Calligonum mongolicum)、沙鞭(Psammochloa villosa)等种群生存,且在沙漠延伸带流动沙丘上已成功建立了梭梭(Haloxylon ammodendron)人工固沙植被,表明在巴丹吉林沙漠南缘建立以乡土植物为主的固沙植被是可行的。在未来研究中,应在山水林田湖草沙生命共同体理念下加强从区域尺度上解析水、植被和沙的关系,系统了解生态系统的原真性、完整性和连通性及生态系统稳定性维持等问题,优化生态景观格局,确定生态保护目标和建设规模,同时要加强对乡土植物适应干旱风沙机制和扩繁保育技术研究,以便为区域生态建设和生态保护提供科技支撑。 相似文献
67.
68.
采用1980-2011年气象台站地面气象要素观测资料、高空探空资料,时间和空间加密气象观测站资料,以及中国气象档案馆原始天气图表等资料,基于沙尘气溶胶浓度(PM10)潜势源地贡献函数PSCF(Potential source contribution function)的沙尘系统追踪方法,发展空气质量气象条件PLAM(……)指数对沙尘天气过程的路径跟踪,给出1980-2011年东北亚沙尘天气过程特征分布;采用Spline趋势分析,讨论沙尘天气系统强度的年变化特征。结果表明:基于气溶胶浓度PSCF函数和气象条件PLAM指数追踪得出,中国和东亚地区沙尘天气过程年际强度变化并非单调减弱,具有历史持续性与转折突变性并存的波状变化趋势,出现准10 a的高低频活动特征。 相似文献
69.
The structural styles can be used to analyses and predict developments and distributions of sand bodies in a rift basin. The dynamic process of faulting and sedimentation can be expressed as follow: the basin topography controlled by fault activity can control water dynamics; which in turn affect the transport and sedimentation of sediments. The corresponding analysis between structural styles and sand depositional types includes the following aspects: (1) in section, the corresponding between development of fault terraces and sand depositional types; (2) in plane, the relationship between faults' association and distributions of sand bodies. There are four types of terrace styles to be identified. They are Steep Slope Single Fault Terrace (SSSFT), Steep Slope Multiple Fault Terrace (SSMFT), Gentle Slope (GS) and Gentle Slope Multiple Fault Terrace (GSMFT), which also can be divided into six subtypes by the timing of the faults activities and the directions of their activity migrations (basinward and landward or marginward). They correspond to the following sand depositions such as alluvial fan, fan delta and turbidite fan etc.. The analysis of structure-sedimentation is a discussion on the rank Ⅲ sequence evolution under the condition of pulsing or episodic fault activities. It has been recognized four plane fault associations such as the comb, the broom, the fork and the fault-fold association as well as the corresponding sand distributions. Structural-sedimentary models above mentioned are significant for the deep oil and gas exploration when lacking of the drill data. It may reduce multiple resolutions in the interpretation of seismic-sedimentary facies and promote sand predictions through the constraints of the structural styles of the basin units. The structural-sedimentary pattern can be used as a geological model in oil and gas exploration in the rift basins. 相似文献
70.
The aeolian sedimentation record of the Thar desert 总被引:1,自引:0,他引:1
A review of the aeolian sedimentary record of the Thar desert is presented. This includes a regional survey of the major dune
forms, their genesis and their relationship to climate and other regional landforms. A key aspect of this work is the chronometry
of the dunes using luminescence methods. Luminescence dating of sand has enabled quantification of the duration of the phases
of sand aggradation and quiescence, time scales of dune migration and the dating of pedogenic carbonates. We demonstrate that
the conventional wisdom of synchronicity of dune aggradation with glacial epoch is not true in the context of Thar sands and
here only a short durationwindow of opportunity existed for dune aggradation. Luminescence ages further suggest that this window occurred during a transitional climatic
regime from glacial to interglacial about 4–10 ka after the glacial epoch. Other inferences included are that:
相似文献
– | • the aeolian activity in the Thar began over > 150 ka, resolving that Thar is not of anthropogenic origin as suggested previously; |
– | • the present spatial extent of the aeolian activity in the Thar is in a contracted stage compared to that in the geological past, which refutes the arguments on its rapid north-eastward expansion; |
– | • the current dune migration rates in areas of significant human-induced disturbances are much higher than during the geological past; |
– | • the monsoon activity in the Thar varied significantly, from being minimal during the isotopic marine stages 4 and 2 to being close to the present during stage 3; |
– | • on shorter time scales the dune activities correlated with the lacustrine records of the region with a phase difference of a few centuries and a periodicity of ∼ 1500 years; |
– | • the sand aggradation climate in the southern margin in Gujarat gradually shrank northwards such that in general dunes older than 10 ka are seen in the extreme southern margin and dunes younger than 2ka ages occur mostly in the western part of Rajasthan. |