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1.
Lin, Z.G. and Wang, S.J., 1988. Collapsibility and deformation characteristics of deep-seated loess in China. Eng. Geol., 25: 271–282. As part of a comprehensive research program, laboratory tests were conducted on samples of deep-seated loess from different locations of the loessial regions of northern China, including Shaanxi, Gansu, Shanxi and Honan Provinces. The information thus acquired on some aspects of the engineering properties of the samples, such as the unit collapse-pressure relationships, the initial collapse pressure versus the “preconsolidation pressure” and deformation–pressure characteristics, is interesting and may prove useful to geotechnical engineers who work on projects on water-poor plateaux or high river terraces in loessial regions throughout the world. 相似文献
2.
In 1985, a programme of research on the sedimentology and diagenesis of the loess and loessic silts of western Europe was initiated jointly by laboratories in Leicester, Meudon, Caen, Milan, Cardiff and Southampton, involving a limited amount of comparative work on the loess from types sites in the Loess Plateau of central China. Preliminary results include the following: (1) Experimental procedures in particle size analysis, clay sample preparation and microscopy have been standardised in all cooperating groups; distinctive fabrics indicative of depositional mechanisms have been recognised. (2) Comparison of aeolian, colluvial and alluvial silt by laser-scanning and bulk magnetic susceptibility anisotropy methods appears to differentiate aeolian silt from loessic silts re-deposited by slope processes and flowing water. (3) The variability in the anisotropy of the limon à doublet facies has been assessed by image analysis of scanning electron microscopy (SEM) and optical microscopy. Strong anisotropy has also been measured in thin section imagery of loess from Normandy and Poland as the product of freezing and thawing. This is confirmed by scanning electron microscopy and by experimental freezing of some silts. (4) The clay fabric and mineralogy in western European loess differ from those in Chinese loess, especially in the case of semi-arid deposits. (5) Distribution of CaCO 3, using thin sections and SEM analysis, has been determined for loess from Normandy and the Rhǒne valley in France and for some Chinese loess, At Saint Vallier, zones of CaCO 3 concentration occur masking much of the original (loess) sedimentary skeleton which is a locally reworked loessic silt with some laminations. Despite considerable scatter, the palaeomagnetic results indicate a reversed polarity throughout, placing the whole Saint Vallier sequence in the Matuyama chron. These preliminary results suggest the existence of two different palaeoenvironments: one typified by central China, with arid glacials and humid interglacials; and the other represented by western Europe, with generally high humidities. There was stronger weathering and soil development and fewer freezing effects on the lossic succession in northern Italy than in western littoral Europe. 相似文献
3.
There is agreement that ultrafine maghemite grains (<100 nm) are responsible for the magnetic enhancement of Chinese loess. Recent studies show that grain size distribution of ultrafine pedogenic maghemite grains within the aeolian sequences on the central Chinese Loess Plateau deposited in the last 8 Ma is consistent. However, whether the observed grain size distribution of ultrafine pedogenic maghemite grains can be observed in the western Chinese Loess Plateau and modern soils is not entirely clear. Here we find that young surface soil samples across the Chinese Loess Plateau and early Neogene loessic soils from the western Chinese Loess Plateau also show consistent grain size distribution with that of ultrafine pedogenic maghemite grains on the central Chinese Loess Plateau. The fact that young surface soil samples show apparent magnetic enhancement suggests that the ultrafine pedogenic maghemite grains derive from oxidation of ultrafine magnetite grains. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
4.
Variations in magnetostratigraphy, pedostratigraphy, grain size and magnetic susceptibility of the loess deposits near Beijing have been studied at two sections. The sections are about 400 km east of the main loess deposits in China, have a maximum thickness of 100 m and extend back to 1.1 Ma. The sequence consists of 14 loess–palaeosol couplets (S0‐S14), which correlate well with sequences in the Loess Plateau. Susceptibility records from the sites near Beijing are comparable to the Xifeng, Luochuan and Baoji sections located in the middle part of the Loess Plateau; however, the down‐core variations in the grain size in the Upper Lishi Formation exhibit some differences. The median grain size increases by about 25–30 µm from L4 to L2, with the sandy grains (>63 µm) increasing from 10–20 wt% to 40–50 wt% . This implies that the depositional environment of the dust sources in the Beijing loess section is different in some aspects from the Loess Plateau. The Beijing loess may have had a different dust source than the Loess Plateau. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
5.
Gao, G., 1988. Formation and development of the structure of collapsing loess in China. Eng. Geol., 25: 235–245. It is well known that in China the regional variations in microstructure of loess are in phase with the overall tendency for collapsibility, gradually decreasing from the northwest to the southeast. These differences are consistent with variations in climatic conditions. This indicates that the structure of collapsing loess is closely related to the climatic condition and geological environment. Based on the microstructure analyses, it can be assumed that the formation and development of the structure of collapsing loess in China has undergone five stages: the loessization stage, the formation stage, the development stage, the degeneration stage and the clayization stage. The five stages of loess regularly exist in different regions of the Loess Plateau. This also shows that under the modern climatic condition the collapsing loess in the northwest of the Loess Plateau in China is still developing. However, the feature of collapsing loess is gradually disappearing in the southeast of the Loess Plateau. 相似文献
6.
甘肃灵台县任家坡黄土－红粘土剖面的磁性地层学研究表明;中国北方连续的风成堆积可下推到705MdB．P。第三纪红粘土的粒度组成从上到下变化很小,与黄土－古土壤序列的粒度大幅度变化形成强烈的反差,意味着晚第三纪时期的气候总体上要比第四纪时期稳定。在705～2．6MaB．P．的红粘土沉积中,可分出的110～115个土壤B层与钙质结核层的组合,初步表明在这个时期有约110～115次气候旋回。 相似文献
7.
当黄土分布区地下水埋深较浅时,黄土常呈饱和状态,不具湿陷性,简称饱和黄土,甘肃引洮供水一期工程总干渠13#、14#、15#隧洞通过饱和黄土,通过常规土工和扫描电子显微镜等综合测试,对饱和黄土的显微结构及化学成分进行了研究,并探讨了其微观结构与物理力学性质及工程特性之间的关系,认为应选择盾构法进行饱和黄土隧洞开挖。 相似文献
8.
对黄河三门峡北岸的山西平陆庙下、阳凹两个黄土剖面研究结果表明,S 6、S 1的磁化率值较黄土高原明显偏高,S 5~S 2的磁化率值则相对偏低,L 7~L 2的磁化率值也表现出较低值,与黄土高原内部L 9磁化率值相近。另外,S 5~L 5地层厚度较大。把两剖面磁化率曲线与曹村剖面黄土-古土壤序列磁化率曲线、深海氧同位素曲线、北半球65°N太阳辐射变化曲线进行对比后表明,两剖面磁化率曲线反映的气候变迁,在0.1Ma尺度上与黄土高原内部基本相同,反映出与地球轨道要素变化控制的太阳辐射变化诱导的全球冰期-间冰期气候旋回的一致性;但并不是简单的一一对应关系,表现在地层厚度较大、磁化率值相对较低。其原因可能有4个:一是粉尘堆积速率不同,二是受流水侵蚀,三是物质来源有别,四是局地的成壤条件差异。 相似文献
9.
黄土堆积松散、湿陷性强且极易被侵蚀的特性导致滑坡、泥石流、水土流失等地质灾害在黄土高原频发。为了缓解当今黄土地区土壤侵蚀,减少地质灾害的发生,本文利用聚丙烯酸钠混合剂对甘肃董志塬重塑黄土进行固化改良。通过室内崩解试验、渗透试验、水流冲蚀试验和三轴压缩试验等手段分析了不同配比下固化黄土的特性差异。结果显示,在经聚丙烯酸钠混合剂固化后,土体抗剪切破坏和水稳性能随着配比的提高而增大。当土体经聚丙烯酸钠混合剂浓度为3.5%的试剂固化后,固化效果趋于最佳,相比未加固土抗崩解和抗冲蚀性能均大幅提高,7次干湿循环后崩解率仅为1.15%,土体剪切破坏时的主应力差在100kPa、200kPa、300kPa围压下分别提高25.29%、28.23%、22.48%,渗透系数降低217.41倍。结合三轴试验数据、粒径级配和场发射扫描电镜从微观结构进行现象和机理解释,聚丙烯酸钠混合剂可将土粒包裹黏接,使土体中细小颗粒团聚在一起,从而改变土体粒径级配,促使土体黏聚力及内摩擦角增大,增强土体抗剪切性能,提高土体水稳性。聚丙烯酸钠混合剂对黄土的固化改良效果良好,将为缓解黄土高原地区土壤侵蚀,防灾减灾提供新方法。 相似文献
10.
Lateral stresses existing in soil deposits are important clues to recent stress history because they tend to remain “locked in” following adjustments in the overburden load: Thus a high lateral stress is partly retained following a reduction in vertical stress, as by glacial melting or erosion. Conversely, during loess deposition a low lateral stress should be retained if the soil structure is preserved under increasing vertical stress. This has not previously been verified in the field because of the difficulty of measuring lateral stresses in situ in an hydrocollapsible material. Tests were conducted at two sites in Missouri river valley loess using theKo Stepped Blade, which uses data extrapolation to give stress on a zero thickness blade. In basal loess where the moisture content was at or above the liquid limit,Ko = 1.0 ± 0.02. In the upper to middle loess zoneKo is as low as 0.2 to 0.4, lower than the values of 0.4 to 0.5 that would be expected if the soil were normally consolidated. Near the ground surface, lateral stresses are higher soKo > 1, attributed to post-depositional weathering and the presence of smectite clay minerals. The vertical sequence of lateral stress from high to low to high again should contribute a tension-induced cleavage if lateral confinement is removed by excavation or erosion. This stress condition is most pronounced in loess close to its source, where the potential tension zone was found to extend to a depth of about 7 m compared to 4 m at the other site. Loess cleavage appears to result from stress relief and is not a unique directional property of this material. 相似文献
11.
Lutenegger, A.J. and Hallberg, G.R., 1988. Stability of loess. Eng. Geol., 25: 247–261. The natural stability of loess soils can be related to fundamental geotechnical properties such as Atterberg limits, water content and void ratio. Field observations of unstable conditions in loess deposits in the upper midwest, U.S.A. show relationships between instability and the in situ moisture content and the liquidity index of the loess. Unstable loess can attain natural moisture contents equal to, or greater than, its liquid limit. Implications of these observations for applied engineering works are described. 相似文献
12.
会宁位于甘肃省中部,气候类型属于典型的黄土高原温带半干旱气候,年降雨量少、蒸发量大,由于特殊的气候条件,该区地表沉积有巨厚的黄土,该黄土具有湿陷性。本文基于作者多年大量的会宁县城段祖历河阶地勘察实际资料,结合地势、地貌和沉积特征,从空间分布、物理力学性质等方面,系统总结了祖历河阶地的岩土工程地质特性,并从场地建筑持力层的选择、地基的处理和基础类型的确定等方面进行了岩土工程对策分析研究,以便为城市的开发和合理利用提供帮助。 相似文献
13.
黄土物源研究对揭示第四纪以来东亚大气环流格局的演化和构造—气候之间的相互作用具有重要意义。目前已应用多种物源示踪方法对黄土物源开展了大量研究,但对黄土物源时空差异规律及其动力学机制尚未取得较为一致的认识。在综合分析黄土物源研究现状的基础上,重点从影响 87Sr/ 86Sr值和 143Nd/ 144Nd 值组成及单颗粒碎屑锆石U-Pb年龄谱构成的因素角度,分析了第四纪黄土的物源及可能变化,获得以下认识: (1)第四纪黄土沉积物的 87Sr/ 86Sr值变化幅度可达0.002 580~0.004 949,远远超出实验室分析测试误差(<0.000 018)或由Sr同位素衰变带来的影响(2.6 Ma时段小于0.000 026,1个冰期旋回小于0.000 001); 143Nd/ 144Nd 值亦发生了较显著变化(0.000 095~0.000 240),其变化幅度远大于实验室的分析测试误差(<0.000 010)及衰变导致的 143Nd/ 144Nd 值(<0.000 013)变化。因此,在黄土中检测到的Sr-Nd同位素组成的变化应具有较明确的地质意义。(2)第四纪黄土沉积物中无论全岩还是主要粒径组分的 87Sr/ 86Sr值和 143Nd/ 144Nd 值的变化都与气候代用指标变化不同步,难以从气候变化角度进行解释,可能更多地反映了源区的变化。(3)与Sr-Nd同位素示踪体系相比,单矿物或单颗粒的物源示踪体系对物源区变化的响应更为敏感,在追踪第四纪黄土沉积物源区时空差异方面具有较明显的优势。(4)基于碎屑锆石U-Pb年龄谱对黄土物源的有限研究揭示黄土高原的黄土在地质历史时期可能发生了原始物源区显著的时空分异,特别是不同剖面都反映出了1.2 Ma前后黄土主要源区的变化,表明通过锆石U-Pb年龄谱研究黄土物源时空差异规律具有揭示岩石圈、大气圈、水圈耦合作用过程及历史的巨大潜力。 相似文献
14.
黄土堆积作为气下沉积,任何一个深度都曾经暴露于地表,因而必然受到相关地表过程的作用.由于这些过程均发生于特定的环境条件下,形成的特征多数具有明确的环境意义;而黄土在沉积后也可能受到各种地质过程的改造,从而对研究中常用的气候代用指标有一定影响.文章基于野外、微形态等分析,结合前人成果,对我国北方新近纪风尘堆积中常见的同沉积和沉积后改造特征、形成过程及环境意义进行研究.由于一些特征在黄土堆积中具有普遍性,可作为识别风成堆积的标志和环境事件研究的指标,并有助于全面理解常用的替代指标的环境意义. 相似文献
15.
Since the late Quaternary Period, the rapid rising of the northeastern Qinghai-Tibetan Plateau has greatly changed the East
Asian climate and formed different regional monsoon climates. Various microstructures of the loess in northern China have
formed under a variety of climatic conditions. The scanning electron microscope (SEM) and energy spectrum analysis are used
in this paper to study the relationship between the indexes of loess microstructures and the forming climates, and the indexes
include the diameter of sand grains, Ca/Fe value and the characteristic shapes of the loess from SEM microstructures pictures.
In terms of their respective climatic circumstances, the major microstructures of regional loess may be classified into nine
categories according to their forms and particle sizes, such as loess formed in near-sand source, loess of granule sand dropping,
and loess formed in hot and rainy places, i.e. with the loess SEM pictures, climates of about 15 ka b.p. in different places may be evaluated. In conclusion, the clear and distinguishable loess microstructures and their indexes
in the Loess Plateau of China can also deduce the evolution of climate, such as warm or cold and wet or dry, and even sandstorm
activities when the loess is deposited. 相似文献
16.
Loesses of the Lower Mississippi Valley (LMV) are world-famous. Sir Charles Lyell (1847), Hilgard (1860), Stafford (1869), Call (1891) and Mabry (1898), thought the LMV loess was a single water deposit although “double submergence” was noted by Call (1891) and Salisbury (1891). Shimek (1902) and Emerson (1918) recognized LMV loess as a wind deposit which came from the valley. Although wind-deposited loess gained wide acceptance, Russell (1944a) published his controversial theory of “loessification” which entailed weathering of backswamp deposits, downslope movement and recharge by carbonates to form loess. Wascher et al. (1947) identified three LMV loesses, mapped distributions and strongly supported eolian deposition. Leighton and Willman (1950), identified four loesses and supported eolian deposition as did Krinitzsky and Turnbull (1967) and Snowden and Priddy (1968), but Krinitzky and Turnbull questioned the deepest loess. Daniels and Young (1968) and Touchet and Daniels (1970) studied the distribution of loesses in south-central Louisiana. West et al. (1980) and Rutledge et al. (1985) studied the source areas and wind directions which deposited the loesses on and adjoining Crowley's Ridge. B.J. Miller and co-workers (Miller et al., 1985, 1986, Miller and Alford, 1985) proposed that the Loveland Silt was Early Wisconsin rather than Illinoian age and advanced the name Sicily Island loess. They proposed the underlying loess was Illinoian and advanced the name Crowley's Ridge. We termed the loesses, from the surface downward, Peoria Loess, Roxana Silt, Loveland/Sicily Island loess, Crowley's Ridge Loess and Marianna loess. Researchers agree that the surfical Peoria Loess is Late Wisconsin and the Roxana Silt is Late to Middle Wisconsin, but little agreement exists on the age of the older loesses. Pye and Johnson (1988) proposed Early Wisconsin for the Loveland/Sicily Island. McKay and Follmer (1985) suggested this loess correlated with a loess under Illinoian till. Clark et al. (1989) agreed on Crowley's Ridge, but suggested the Loveland/Sicily Island loess on Sicily Island was older. Mirecki and Miller (1994) and Millard and Maat (1994) suggested an Illinoian age for the Loveland/Sicily Island loess. Miller and co-workers suggested, as did Pye and Johnson (1988), an Illinoian age for the Crowley's Ridge loess. McKay and Follmer (1985) suggested it correlated with a loess under “Kansan” till. Stratigraphy indicates the Marianna is the older of the five loesses. Researchers identified loess on both the east and west side of the LMV as well as on higher terraces within the valley. Many researchers assumed unaltered loesses were commonly yellowish brown, and silts or silt loams (West et al., 1980; Miller et al., 1986). The nonclay fraction of unweathered LMV loesses was dominated by quartz followed * Corresponding author. by carbonates, mainly dolomites, followed by feldspars, and micas. Clays were dominated by montmorillonite followed by micaceous minerals, kaolinite and vermiculite (Miller et al., 1986). Soils in the Crowley's Ridge loess are most developed, followed by the soils in the Loveland/Sicily Island which are more developed than the modern soils in the Peoria Loess. Soils in the Roxana and Marianna loesses are least developed and the Farmdale Soil of the Roxana is the weaker of the two (Miller et al., 1986). There is certainly overlapping range in the degree of soil development in the various loesses. 相似文献
17.
To identify the weathering intensity and to deduce the provenance of sediments (black-brown soil and loess) from the loess
tableland in the Liyang Plain is of great importance for understanding the development and origin of civilization of this
critical region in China. The geochemical results show similar REE distribution patterns among sediments sampled from the
YC profile in the Liyang Plain, reticulated red soils from the Dongting lake area, Xiashu loess in Zhenjiang, and loess from
the Loess Plateau in China. These similarities imply a single provenance, from dust storms. REEs, especially the LREE/HREE
ratio and Eu anomaly, can trace weathering intensity. Higher LREE/HREE ratios, and remarkably Eu anomalies, are present in
the top loess (L 0), Lower LREE/HREE ratios and insignificant Eu anomalies are present in black-brown soil (S 0*) from the Liyang Plain. These demonstrate that the black-brown soils have undergone a lower intensity of weathering than
the loess of YC profile. Moreover, CIA values for sediments from the YC profile provide powerful evidence to support the above
result. Comparisons of analyses of the REE contents of sediments from the YC profile, of reticulated red soils from the Dongting
Lake area, Xiashu loess from the Yangtze River, and loess from the Loess Plateau, clearly show the weathering intensity decreases
according to the following sequence: reticulated red soil from the Dongting Lake area > sediments of YC profile from the Liyang
Plain, which formed from dust storms ≈ Xiashu loess from lower reach of the Yangtze River > loess from the Loess Plateau. 相似文献
18.
粒度分布曲线是土壤最基本的土性参数之一,通过数学方程预测粒度分布曲线将为工程勘察节省大量成本。Fred?
lund建立在Fredlund和Xing土水特征曲线方程基础上的粒度分布曲线方程已被证明适用于多种土类,但其对中国黄土的有
效性很少得到验证。本文采用Fredlund粒度分布曲线方程对黄土高原7个地区18个黄土样的粒度分布曲线进行了拟合,结
果表明Fredlund粒度分布曲线方程与中国黄土的粒度分布曲线拟合度高,拟合参数稳定且呈规律性变化,能够很好地反映
中国黄土的地域性。本文得到的参数可用于各个地区的粒度分布曲线预测,并对黄土粒径分析及分类具有指导意义。 相似文献
19.
青海湖地区的晚第四纪黄土记录了湖区晚第四纪以来的环境和气候变化.迄今为止,对于青海湖地区晚第四纪黄土物质来源的研究较薄弱.以青海湖东岸的种羊场晚第四纪风成沉积剖面为主要研究对象,在青海湖区及其周边采集了黄土、风成砂、湖相沉积、河流沉积等样品,结合黄土高原西部临洮黄土样品,对它们的元素组成(＜75 μm的硅酸盐组分)进行了对比研究.初步结果表明:(1) K 2O/Al 2O 3(摩尔比)和Zr/Ti、Zr/Nb比值显示青海湖地区的风成沉积显著区别于本区的河流沉积和湖相沉积;(2) 青海湖地区的晚第四纪黄土与黄土高原西部临洮黄土的K 2O/Al 2O 3和Zr/Ti、Zr/Nb比值相一致;(3) 青海湖地区的晚第四纪黄土可能来自柴达木盆地. 相似文献
20.
The geology of loess in China involves many problems. This paper deals only with the basic ones of the or-igin of loess. the geologic setting and palaeoenvironmental evolution leading to the formation of the Loess Pla-teau. and the regional stratigraphy of loess deposits. particularly the last problem. A better knowledge of theformation and development of the loess deposits in China has been obtained through analysis and correlationof lithostratigraphy. biostratigraphy, magnetostratigraphy. climatostratigraphy and chronostratigraphy. 相似文献
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