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砂土层在地面沉降过程中呈现一定的蠕变特性。文章采用一维压缩试验对4 MPa 下砂土的变形特征进行了研究,并
采用改进的试验装置对砂土的微观结构进行了提取。通过对8 组不同级配砂土样的蠕变特性和微观结构分析,得到如下结
论：粒径单一的砂土在蠕变过程中更容易出现突变,砂粒受力后更容易发生破碎,产生滑移错动;砂土蠕变的蠕变量与砂
粒级配密切相关,砂土的粒径越单一且粒径越大时,砂土的蠕变量也越大;采用表征砂土颗粒形状复杂程度的形状系数,
从微观上定量分析了砂土在蠕变过程中发生破碎的情况和蠕变量大小,且形状系数越小,表明该种砂土形状越复杂,在蠕
变过程中砂土的破碎性越高,蠕变量越大。 相似文献
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四川盆地厚坝侏罗系大型油砂矿藏的成藏主控因素 总被引：1，自引：0，他引：1
厚坝侏罗系大型油砂矿藏位于四川省江油市,龙门山北段推覆体构造带的单斜构造单元内,地表出露大量的侏罗系沙溪庙组下段的含油砂岩,经钻井证实油砂资源丰富,油砂层的平均厚度为34.7 m,平均含油率为9.46%,初步估算0～500 m埋深的油砂分布面积为26.79 km2。通过研究区详细的石油地质和地球化学的研究发现,厚坝侏罗系大型油砂矿藏的成藏主控因素为：①寒武系烃源岩为厚坝侏罗系大型油砂矿藏提供了充足的油源;②储集层砂岩含油率高、油砂层厚、储集物性和储集空间良好;③龙门山北段区域构造带控制了油砂成矿带的形成与分布,逆冲断层、节理发育带与高孔隙度中-粗砂岩的良好配置是油砂形成的最有利形成条件,而喜山期构造掀斜、断裂输导和山前剥蚀是油砂形成和保存的必要条件。 相似文献
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根据钙质砂中桩基工程的现状,针对取自南沙群岛永暑礁的钙质砂,设计一个室内模型试验装置来研究钙质砂中钢管桩的承载和变形性能以及影响因素,并进行了石英砂中的对比试验。试验结果表明,钢管桩在钙质砂和石英砂中的表现有着显著差异。钙质砂中钢管桩承载能力很低,仅为石英砂的66%～70%,钙质砂中桩身轴力衰减速率缓慢,桩侧摩阻力远远小于石英砂的,仅为石英砂的20%～27%,并具有深度效应,开口钢管桩和闭口钢管桩的桩侧摩阻力相差不大。同时表明,钙质砂中桩侧摩阻力对相对密度的变化没有石英砂敏感,受相对密度影响很小。由颗粒破碎引起的桩周水平有效应力的大幅降低是造成钙质砂中钢管桩桩侧摩阻力低的主要原因。 相似文献
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Trace element and REE geochemistry of fine- and coarse-grained sands in the Ordos deserts and links with sediments in surrounding areas 总被引：1，自引：0，他引：1
Wenbo Rao Hongbing Tan Sanyuan Jiang Jiansheng Chen 《Chemie der Erde / Geochemistry》2011,(2):155-170
In addition to mineral analyses, REE and trace element geochemical characteristics of fine- and coarse-grained sands in the Ordos deserts and other sediments in surrounding areas are investigated.Commonly the samples consist of quartz, feldspar and muscovite and less clinochlore, dolomite and ankerite. In few samples muscovite is absent.REE and trace compositions are spatially uniform for the same grain-size sands, suggesting that they could have the same sources or/and were well homogenized. However, fine- and coarse-grained sands in the Ordos deserts show different REE and trace element compositions. Fine-grained sands show higher contents of REE and trace elements than those of coarse-grained sands. They differ in Eu anomalies and (La/Yb)N ratios although both fractions are characterized by the steep LREE and smooth HREE patterns. The fine- and coarse-grained sands are also distinct in some characteristic element ratios (e.g., Th/Co, La/Sc, Th/Sc and Y/Ni).REE and trace element patterns of the two different grain-size fractions are closely associated with geological properties of individual sources rather than the mineralogical differentiation induced by wind sorting. The coarse-grained sands mainly resulted from sandstone weathering in the Ordos deserts and movements of coarse particles by wind. REE and trace element patterns of fine-grained sands in the Ordos deserts differ from those of sandstones in the Ordos deserts, the alluvial sands in the surrounding mountains and the coarse fluvial sands in the Yellow River. They resemble the fine fluvial sands in the Yellow River. In addition, arid areas of Northwest China such as the Tarim Basin and the Alxa Plateau should not be ruled out as the source of the fine-grained sands in the Ordos deserts because these arid areas reserve plenty of fine-grained sediments and also located in the upwind directions of the Ordos deserts. 相似文献
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尾矿砂的动力特性研究 总被引：2，自引：2，他引：2
目前国内许多尾矿坝的初始坝本身不透水且无排渗设施,因而整个尾矿坝体浸润线很高,坝内大部分尾矿砂处于饱和状态。在动荷载的作用下,这些尾矿砂的动力特性对尾矿坝的安全稳定具有重要的意义。本文利用液压式振动三轴仪,研究了某尾矿坝内尾矿砂的动力特性,讨论了影响尾矿砂液化的因素。 相似文献
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珊瑚砂属珊瑚礁碎屑土,是一种特殊的地质体,具有典型的疏松多孔、硬度低、易碎的特点,由于珊瑚礁仅分布在热带海域,往往位于远离大陆的礁岛,当前对珊瑚礁岩土的勘察研究较少,相关规范也尚未涉及。以实际工程为对象,对东帝汶某珊瑚砂场地的工程性质进行了一些探讨,从标准贯人试验和钻孔剪切波速试验等原位试验结果进行分析,借鉴了目前石英砂工程性质的评价方法作为对珊瑚砂工程性质判断的参考,对珊瑚砂的强度特性和地震液化特性进行了讨论。相对石英砂的一般性质而言,珊瑚砂的标贯击数较低而相应的剪切波速相对较大,珊瑚砂在地震作用下液化的可能性较大。 相似文献
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海岸现代风成砂粒度参数特征的研究--以中国温带海岸为例 总被引：6，自引：1，他引：6
现代海岸风成砂的粒度特征是海岸风沙研究的重要问题,本文以我国温带海岸为研究区域,利用 136个现代海岸风成砂样数据,通过粒度组成、平均粒径、标准偏差和偏差、峰态等粒度参数分析了其粒度特征。结果表明,我国温带海岸的现代风成砂并非过去认为的几乎全由分选很好的细砂组成,是以正偏为主,粒度参数的地域差异明显,并随沙丘类型、规模及距海岸线的远近不同等而变化。与海滩砂比较,风成砂具有普遍含有粉沙、略细、多正偏、峰态偏窄等特点,但利用粒度参数散点图和因子分析法二者均无法区分。我国温带海岸现代海岸风成砂粒度参数的上述特征与其特有的发育条件和演化过程密切相关,其中主要与季风气候特征显著、形成时间短、风力作用时间有限以及风沙活动空间狭小并受到水力与重力作用的干扰等有关。 相似文献
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混积岩一例--滇东震旦系陡山沱组砂质砂屑白云岩的成因 总被引：11，自引：2，他引：9
滇东震旦系陡山沱组顶部的砂质砂屑白云岩是一例典型的混积岩,即狭义的混合沉积。岩石中的石英砂分选好,圆度和球度高,它们时稀时密地呈“悬浮”状散布在白云石砂屑沉积物中。其产状及结构构造特征表明,它是当时的海滩砂在海进过程中被搬运到海洋中,并与白云石砂屑混合而形成的。 相似文献
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Petrology of glacial sand: implications for the origin and mechanical durability of lithic fragments
The petrology of first cycle (unmodified) and second cycle (reworked) sand at the termini of eleven valley glaciers eroding coarse- to fine-grained bedrock types is determined in order to evaluate the origin and mechanical durability of lithic sands. First cycle sands are coarse- to medium-grained, poorly sorted, fine-skewed, non-modal lithic sands with an average composition of Q21F6L73. Grain-size distributions do not vary with composition or source rock types, although sands derived from finer grained source rocks contain more lithic fragments than sands from coarser grained sources. By contrast, second cycle sands are medium-grained, poorly sorted, fine- to coarse-skewed arkosic to lithic sands with an average composition of Q19F40L41, and contain fewer lithic fragments than do first cycle sands. We propose that the origin, mechanical durability and survival potential of lithic fragments are related to the types and abundances of their internal planes of weakness, and the particular stress field of the transporting medium. As a result of abrasion, glacial clasts and lithic fragments are subjected to shear stress so that fractures propagate along intracrystal and intercrystal planes of weakness resulting in a continuous grain-size spectrum of lithic fragments and monomineralic grains irrespective of the type of source rock. Upon subsequent aqueous transport in the proglacial environment lithic fragments are subjected to point-loading during saltation in addition to shear stress. Point-loading produces extensional fractures which preferentially propagate along intercrystal planes of weakness, so the lithic fragments break into smaller monomineralic grains and/or lithic fragments. Lithic fragments of very coarse sand-size are abundant in first cycle sands, thus refuting, at least for glacial sands, the widely held view that grains of this size are deficient in nature. The presence of fewer grains of this size in second cycle sands indicates that very coarse sand-size lithic fragments can survive recycling, but in greatly reduced proportions due to breakage. 相似文献
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Uppermost sands of the Red Crag at Walton-on-the-Naze (Essex) and elsewhere in East Anglia have been decalcified to iron-stained quartz sands. In contrast, lower sands are only minimally altered and contain aragonitic and calcitic shells. Aragonitic shells are slightly dissolved (chalkified), but calcitic shells are unaffected. Cementation is limited to an addition of iron oxides, now mainly haematite, which also coat carbonate grains. Abundant iron-oxide fines in the upper decalcified sands were liberated from the coatings of shells; shells that have since dissolved. The diagenetic nature of the contact between decalcified upper and unaffected lower sands is evident where it transects cross-bedding. The contact is knife-sharp, even smoothly truncating large shells, and is usually planar and subhorizontal. Shelly sands immediately beneath the boundary contain similar amounts of aragonitic material, as do sands further below. Locally the decalcification boundary has been contorted by cryoturbation, implying that carbonate dissolution was a Pleistocene event. Decalcification probably occurred when the area was affected by permafrost. Lower sands were cemented by ice and protected from dissolution. Upper sands were above the ice table and subject to chemically aggressive waters during summer thaws. Decalcification is believed to have taken place during an episode of climate amelioration when downward retreat of the ice table accompanied replacement of tundra by boreal forest. Highly acidic and podzolic soils developed, beneath which shell-carbonate dissolved. Sharp based decalcified zones in Lowestoft Till and Devensian deposits in other parts of England can also be attributed to dissolution associated with permafrost. 相似文献
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在溜砂坡系列研究之二的基础上,对风干砂的运动特征进行了细致观察。将干砂流视为连续介质的流动,对干砂流的运动动力和阻力进行了深入研究,建立了干砂流垂线流速分布方程和干砂流体底面、表面滑动速度方程。结合挡砂工程,将干砂流体视为沿底面（此种砂坡的天然休止角）滑动的三角体,从而导出粒状碎屑溜砂坡水平土压力（或水平推力）计算模型。 相似文献
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Juan Jos Kasper-Zubillaga Beatriz Acevedo-Vargas Ofelia Morton Bermea Glicinia Ortiz Zamora 《Chemie der Erde / Geochemistry》2008,68(1):45-59
Twenty-one surficial sand samples from the Altar Desert coastal and desert dune systems were analysed for rare earth elements (REE) content. This was done to observe the provenance signatures for four strategic dune localities near the Colorado River Delta, the El Pinacate dune fields, and the beaches of the north of the Gulf of California in the state of Sonora, Mexico. Our goals are to show which mechanisms (i.e., aeolian, marine) exert more influence on the composition of the Altar Desert dune sands. This study also shows the usefulness of REE spatial distribution to determine the relative mobility of the sand. Some sand samples from the dune systems in San Luis Río Colorado (SLRC), Golfo de Santa Clara (GSC), and Puerto Peñasco (PP) displayed dissimilar REE concentrations with respect to the rest of the sand samples from the same sites. These differences can be related to short aeolian transport distance in the sands with high REE concentrations and long aeolian transport distance in the sands with low REE concentrations. Besides, high REE concentration in the sands might be due to their closeness to the Colorado River Delta sediments and to recycled sands derived from granitic rocks. In contrast, all the sand samples from the El Pinacate (EP) site have similar REE concentration values, suggesting that the El Pinacate dune sands are influenced by more selective aeolian processes and less diverse heavy mineral content. The Altar Desert dune sands are derived from granitic sources eroded by the Colorado River. Our results also indicate that the Altar Desert dune sands are low in heavy mineral content (with the exception of Fe and Ti bearing minerals) and enriched in carbonates with phosphates (especially at the PP site) yielding poor correlations between REE and major element concentrations. The REE geographical distribution values in the Altar Desert dune sands indicate that light and heavy REE concentration values are related to aeolian transport, maturity of the sands, their low weathering rates, proximity of the source rocks, and the biogenic debris input from beach sands into the dune. 相似文献
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Samir M Zaid 《Journal of Earth System Science》2017,126(4):50
Texture, mineralogy, and major and trace element geochemistry of 26 coastal dune sand samples were studied to determine the provenance and tectonic environment of two dune fields close to the beaches of Safaga (SF) and Quseir (QS) at the Egyptian Red Sea coast. Onshore winds generate fine, moderate, moderately-well to well-sorted, coarse-skewed to near-symmetrical dune sands with mesokurtic distributions. Winds pick up and transport grains from nearby beach sands and alluvial deposits into a wide Red Sea coastal plain at the border of the beach. The mineralogical (Qt–Ft–Lt) and geochemical composition of the sands, indicate that SF and QS coastal dune sands are mature and influenced by quartz-rich sands. The average CIA values in SF and QS coastal dune sands are low relative to the range of the PAAS, suggesting an arid climate and a low intensity of chemical weathering. The SF and QS coastal dune sand samples are plotted in the recycled orogen and partly in craton interior fields suggesting recycled older sedimentary and partly metamorphic-plutonic sources. The high content of quartz with shell debris and carbonates in coastal dune sands support the recycled sedimentary beach and alluvial sand sources. The dominance of heavy minerals like amphiboles (hornblende) and biotite in the coastal dune sands also supports the effect of metamorphic-plutonic source rocks. The new tectonic discriminant-function diagrams suggest that the coastal dune sands were deposited in a passive margin of a synrift basin. The results provide a good evidence for the extension in the Red Sea rift system during Oligocene-post Pliocene, which is consistent with the general geology of Egypt. 相似文献
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准噶尔盆地西北缘风城油砂分布特征及成矿条件 总被引：1，自引：0，他引：1
准噶尔盆地西北缘风城地区蕴含着丰富的油砂资源,地表出露油砂形成多座规模不等的油砂山丘,面积约8km2,油砂主要存在于白垩系吐谷鲁组,连片集中、厚度大。风城下伏地层油砂分布面积大,层位稳定,产状缓,也主要分布在白垩统吐谷鲁组、上侏罗统齐古组中,含油率高、油质较好。该区油砂资源主要来源于玛纳斯湖凹陷二叠系烃源岩,这套烃源岩中生成的油气沿着该地区发育的断裂和不整合面向上运聚。断裂、不整合面及砂体的分布叠置构成了运移系统,有效的砂体既是运移通道又是储集体,最后建立了该区远源次生的油砂成矿模式。 相似文献
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Fei Han Mingzhong Tian Fadong Wu Jianping Zhang Siwen Liu Lulin Wang 《Arabian Journal of Geosciences》2017,10(11):241
This study here is the result of a comparative study of the geomorphic features, grain size distribution, major mineral components, and micro-textures of sound-producing and soundless sands from three geoparks in north China, and discusses the possible causes of this naturally occurring, physical phenomenon. The sound-producing sand dunes we have investigated are situated along a curvilinear belt of deserts and experience variable precipitation–evaporation rates on a yearly basis. “Singing sands” occur mainly on barchan-type dunes and adjacent to lakes or springs, whereas soundless sands are mainly located in desert areas where there is no nearby surface or groundwater sources. We have analyzed samples from nine sound-producing and two soundless sand dunes using grain size, X-ray diffraction and fluorescence, and SEM analyses. All sand types are composed largely of quartz and feldspar, but sound-producing sands also contain secondary minerals such as kaolinite (3–5%), albite (2–6%), microcline (2–5%), and calcite (5%) that are lacking in the soundless sand samples. Sound-producing sands are generally fine-grained whereas soundless sands are coarse-grained, and all sand types are generally sub-rounded to rounded indicating long transport distance from their provenance. Sphericity values of both sand types are nearly identical with predominantly oblate shapes. Surface pitting is not a unique feature of either sand types, and hence can be ruled out as a major cause of the acoustic properties of sound-producing sands. Densely distributed dissolution features such as scale-like upturned plates and silica scales on grain surfaces contribute significantly to the sound emission of singing sands. Thus, the physical–climatic conditions in deserts such as the presence of surface water and groundwater and precipitation–evaporation rates, which collectively control the formation and distribution of dissolution features on sand surfaces, have a first-order control on the production of sound-producing sands. 相似文献
19.
Rippled flanks of longitudinal dunes and the slip faces of various dune types can be distinguished granulometrically by comparing the top to bottom trend of changes of sorting in the sand population of each individual slope. Flank sands, which are prone to sorting processes through migration of ripples alongslope, are always better sorted upslope whereas slipface sands, which are controlled by avalanche and grainfall of sands, become better sorted downslope. Considering the absolute values of the bottom samples, the sands of the slip faces are both better sorted and the size distribution more symmetrical than those of the rippled flanks. Applying this approach in investigating ancient sediments could improve palaeogeographical interpretations. 相似文献
20.
Geochemical and isotopic studies of aeolian sediments in China 总被引：5，自引：0，他引：5
The Sr and Nd isotopic, rare earth element (REE) and major element compositions, together with mineral and grain‐size proportions, are reported for aeolian loess deposits and desert sands from several Chinese localities. The study was carried out in order to examine regional variations in the isotopic and geochemical features of these aeolian sediments, and to constrain the provenance of Chinese loess. Samples include loesses from the Tarim and Junggar basins and desert sands from the Taklimakan desert in north‐west China, loess from the Ordos area and desert sands from the Tengger and Mu‐us deserts in north‐central China, as well as loess and desert sands from the Naiman area, north‐east China. REE distributions show minimal variation among the Chinese loess deposits, whereas those for the desert sands show regional variations. New isotopic data document a latitudinal variation in Sr and Nd isotopic features for the loesses and desert sands. The Naiman and Junggar loesses have distinctly lower 87Sr/86Sr ratios and higher εNd(0) values than the loesses from the Tarim Basin, the Ordos area and the Loess Plateau. Among the desert sands, the Naiman samples have higher εNd(0) values than the Taklimakan, Tengger and Mu‐us samples. Isotopic data suggest that loesses of the Loess Plateau were supplied from the Tarim Basin loesses and Taklimakan Desert sand, and that the Naiman loesses were supplied from the Junggar Basin loesses. The latitudinal variation in the loesses and desert sands may be partly explained by isotopic variations reported previously for moraines from the Tianshan and west Kunlun Mountains, which are possible sources for the loesses and desert sands. These inferences on the provenance of the loesses and desert sands are consistent with the dust transport pattern over East Asia. 相似文献