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1.
黄土的构度指标及其试验确定方法 总被引：4，自引：4，他引：0
黄土的结构性是一个重要的物理性质指标,它与土的粒度、密度和湿度一起影响土的力学性质。依据加荷、扰动、浸水释放土结构势的方法,由土的无侧限抗压强度定义了黄土结构性的构度指标。通过多个场地不同黄土的无侧限单轴压缩试验,测试分析了不同含水率原状土、重塑土和饱和原状土的单轴压缩应力-应变曲线及无侧限抗压强度变化规律,由此得出土的构度指标的变化规律。并且,在粒度、密度、湿度相似条件下,比较分析了土的构度指标与其压缩性之间的关系。土的构度指标与粒度、密度和湿度指标一起能够合理描述土的物理力学基本性质。 相似文献
2.
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
3.
E.M. Rutledge M.J. Guccione H.W. Markewich D.A. Wysocki L.B. Ward 《Engineering Geology》1996,45(1-4):167-183
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
4.
JERZY NAWROCKI OLGA POLECHOSKA REJ BOGUCKIJ MARIA &#;ANCZONT 《Boreas: An International Journal of Quaternary Research》2006,35(2):266-271
Studies of the anisotropy of magnetic susceptibility (AMS) were carried out in order to define the directions and strength of palaeowind during the sedimentation of the youngest loesses in Poland and western Ukraine. These sediments, like the Chinese and Alaskan loesses, appear suitable for application of the AMS method. The inclined mean minimum axes were considered as reflecting the prevailing palaeowind direction at the time of loess sedimentation. The majority of the sections studied indicate a palaeowind direction from W-SW to E-NE, with a mean azimuth of 258°. This direction corresponds to the strike of the Weichselian ice-sheet margin and is parallel to the axis of the lowland between the ice-sheet margin to the north and the Carpathian Mountains and the Podole Upland to the south. Further AMS studies of the oldest parts of loess sequences in Poland and western Ukraine may help in reconstruction of the atmospheric circulation in this part of Europe since c. 900 kyr BP. 相似文献
5.
湿载耦合条件下结构性黄土的压缩变形模式研究 总被引：1，自引：0，他引：1
对不同含水率的杨凌、青海结构性黄土进行压缩试验,依据变形等效原则,用同一固结孔隙比下非饱和黄土与相同干密度饱和黄土的应力之差定义了结构流体等效应力,提出了压缩应力条件下结构性黄土的有效应力原理。探讨了结构流体等效应力与饱和度（含水率）及应力之间的关系,发现含水率较低时黄土的结构流体等效应力与应力之间呈线性关系,并基于此结构流体等效应力,提出了湿载耦合时结构流体等效应力的表达式。依据压缩应力条件下结构性黄土的有效应力原理,引入能够反映结构性变化的结构流体等效应力,在饱和黄土压缩曲线的基础上建立了结构性黄土压缩曲线模式,根据此模式可以确定湿载耦合时的总应力压缩曲线和有效应力压缩曲线,计算结果与试验结果吻合较好,为计算其增湿湿陷变形提供了一条新的途径。 相似文献
6.
《Earth》2006,74(3-4):309-316
Loesses form wide belts in front of previously glaciated areas. Their thicknesses may be considerable, changing in Eurasia from maximally a few metres in the west to a hundred metres or more in the east. The Eastern (particularly Chinese) loesses are mostly unrelated to glaciations. The periglacial loesses from China and elsewhere predominantly date from the last Pleistocene glaciation: relatively few comparable occurrences are known from earlier Quaternary glaciations. As it is difficult to imagine that the conditions in front of the land-ice masses during the earlier glaciations differed fundamentally from those of the last one, considerable quantities of loess must have disappeared. This disappearance, which is commonly ascribed to fluvial and eolian erosion, is not easily explained as equivalent deposits that may have the older loesses as a source, are practically absent. A possible explanation might be that loess is recycled during successive glaciations. Some loess disappears during interglacials by erosion, but this quantity is more than compensated by the formation of new silt particles. The implication would be that the loess deposits increase in volume for each new glaciation. 相似文献
7.
A comparison of the geochemical features of loesses of New Zealand and China indicates that the distributions of the elements and their variations reflect the fluctuations of climate which can be compared with the oxygen isotope stages and glacial periods.New Zialand loess is different in source from Chinese loess.Therefore ,some differences are also noticed in their chemical compositions .Loess accumulation in New Zealand is later than that in China.Because of more rainfall in New Zealand and different distributions of loess the elements in loess have suffered stronger leaching than in China. 相似文献
8.
不同地区非饱和黄土动力结构性研究 总被引：3，自引：0，他引：3
对兰州、洛川、杨凌地区黄土在不同含水率与不同应力状态下进行动扭剪三轴试验,测定了黄土的动剪应力-应变关系曲线;同时,依据Hardin-Drnevich双曲线模型,改进了基于动剪应力考虑的土结构性定量化参数,并应用该参数对三地区非饱和黄土的动力结构性进行了分析。结果表明,三地区非饱和黄土的动力结构性参数随动剪应变的增大先降低,而后保持在一个稳定的水平;含水率与固结应力对黄土的动力结构性影响显著,在相同的固结应力条件下,含水率越低,黄土的动力结构性参数越大,在相同的含水率条件下,固结应力越小,黄土的动力结构性参数越大;在相同的条件下,杨凌地区黄土的动力结构性最强,洛川地区黄土次之,兰州地区黄土最弱,即黄土的动力结构性在地理空间分布上存在从西北向东南方向增强的规律。 相似文献
9.
J. Buraczynski 《Engineering Geology》1988,25(2-4):201-208
Buraczynski, J., 1988. Lithological, mineralogical and geochemical characteristics of loess in the Rhinegraben. Eng. Geol., 25: 201–208.
Lithological properties of loesses have considerable practical significance. Together with the origin of the material and the genetic–facial variability they are characterised by granulometry, chemical and mineral composition and textural features. In particular, the clay fraction and carbonate content point to the fraction and carbonate content point to the geotecnical properties of loesses. 相似文献
10.
11.
川西高原甘孜黄土地层学 总被引：23，自引：2，他引：23
本文初步研究了甘孜黄土地层，实测了甘孜县城西南郊新市区和满地两剖面，它们分别厚２３．７ｍ和２６．０ｍ。根据岩性、磁性地层特征、磁化率、ＣａＣＯ３质量分数测定和热释光测年结果，甘孜黄土可划分为冰后期Ｓ０复合古土壤，末次冰期Ｌ１复合黄土和末次间冰期Ｓ１复合古土壤等３个地层单位。布莱克反向极性亚时记录于底部Ｓ１ＬＬ１黄土中。甘孜黄土沉积始于晚更新世早期，大约为１２０ｋａＢＰ。甘孜黄土的磁化率变化反映了最近１２０ｋａ来的高原季风演化和气候环境变迁，６个磁化率高值段指示了６个夏季风环流增强的时段，６个磁化率低值段则 相似文献
12.
Dr. S. S. Savvateev Dr. N. I. Kriger Dr. S. A. Lavrusevich Dr. A. G. Petrov 《GeoJournal》1987,15(2):173-176
The properties of loesses are very peculiar. The formation of loess is stable in the dry state, but under the effect of moisture it could present great subsidence. Sometimes in loess some processes are in progress. Similar to karst formation in the water-soluble rocks, but chiefly connected with mechanical suffosion (loess pseudokarst). In the water saturated condition loess soils are of a lower bearing capacity. Locally the loess is characterized by some self-progressing processes of underflooding by underground waters. Provoked by earthquakes and explosions some thixotropical liquefaction of loess soils may occur. All these processes have drawn the attention of researchers, engineers and agronomists of different countries to loess. In the first part of this paper we consider the collapse deformations and wash-outs of loess (Savvateev 1974), in the second part — pseudokarst processes (Kriger; Lavrusevich; Petrov 1983). 相似文献
13.
B. Grabowska-Olszewska 《Engineering Geology》1988,25(2-4):177-199
Grabowska-Olszewska, B., 1988. Engineering-geological problems of loess in Poland. Eng. Geol., 25: 177–199.
In Poland, loess covers are limited to a latitudinal belt in the southern part of the country. The covers vary from 2 to 30 m in thickness and the loesses are developed in three major facies: eolian, deluvial and alluvial. Stratigraphically, they represent four major horizons correlated with the Vistulian (Würm) Glaciation and some older ones. The paper presents characteristics of granulometric, mineral and chemical compositions with reference to origin, facies and stratigraphic position of these soils, as well as their lithofacies classification. The classification gives the basis for analysis of local and regional variability in engineering-geological properties of the loess. 相似文献
14.
多瑙河中游盆地黄土和其它陆相层序 总被引：1，自引：0，他引：1
文章叙述了多瑙河中游盆地的第四系黄土与古土壤层序。一般第四纪下降盆地的黄土、砂及古土壤层的层序两倍于抬升的黄土高原及山坡部位所见到的数量，因此能划分得更详细。利用盆地中划分的层序重建的古气候特征可以表征大小不同的区域性差别，同样亦可揭示不同时代的差异。根据冷黄土、埋藏溪流、河阶地等的位置，亦可根据不同古生物的指示，可获得某些气候类型（旱冷的、湿冷的）的重要信息。应用米兰柯维奇曲线根据岩性地层学的研究重建了过去事件的新时间表 相似文献
15.
美国技术标准用弦线模量对我国技术更新的启示 总被引：1，自引：1，他引：0
用弦线模量计算地基变形是中国的原始自主创新。它改正了压缩模量和各种计算模型存在的问题,所以对计算结果有很大的改进。它依据土性物理指标用软件计算,是各种计算方法中最简单的方法。用于地基设计规范能够实现以变形控制设计的目标;用于黄土地区建筑规范,能够依据基础面积、基底压力、相邻基础影响等条件,并考虑地区差异、土性的微结构差异等条件真实地计算不同类型黄土的湿陷量,实现定量评价黄土湿陷性的目标。在中国对弦线模量研究的同时,美国在金属材料非线弹性变形计算中也研究并已经在其技术标准中采用了弦线模量代替杨氏模量,中国的同类标准也引用了它。这对在我国地基规范中采用弦线模量法进行技术更新,应该具有重要的启示作用。在简要介绍弦线模量法主要情况的基础上,进一步阐明这一观点。 相似文献
16.
Dr. Ulrich Manze Dr. John C. Vogel Dr. Reinhard Streit Prof. Dr. Karl Brunnacker 《International Journal of Earth Sciences》1974,63(3):885-897
The ratio of oxygen and carbon isotopes is a criterion for the carbonate-genesis with distinct differences between marine, freshwater, soil and loess carbonates. In addition it becomes clear that there is a number of carbonate soils within the loess of the mediterranean region with distinguishable isotopic compositions. The components affecting the relation of the isotopes in these loesses and the intercalated soils are discussed. The carbonate-turnover during the sedimentation of the loess with carbonate-precipitation from remnant solutions seems to be of some importance. The relatively small participation of biogenic CO2 in the carbonate-turnover ist evident. 相似文献
17.
18.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(5):475-478
Typical loess-palaeosol formations in the southern part of the Russian plain (Novaya Etuliya type section), in China and in Central Asia show the same pattern of magnetic susceptibility (MS) variations with enhanced signatures in soils compared to loesses. This behavior is well known to be caused by in situ forming fine grained magnetite (maghemite) of pedogenic origin. A different pattern of MS changes has been reported for Western Siberia and Alaska: high magnetic signatures in loesses and low ones in palaeosols. The highest MS values in the Belovo type section (Ob River) are connected with the sand and silt fractions and hence are due to sedimentary processes and terrigenous magnetic minerals. Low MS in palaeosols is related to gleisation. A more complex behaviour of ms changes is observed in the Precaucasus loess section at Otkaznoe. The palaeosols here show enhanced magnetic signatures whereas the loess horizons display largely variable magnetic signals due to changing detrital material influx. 相似文献
19.
应力路径试验前后不同黄土的孔隙分形特征 总被引：1，自引：0，他引：1
为了解不同黄土孔隙形状复杂程度的差异和应力路径对孔隙形状复杂程度的影响,对两种黄土应力路径前后孔隙分形特征进行了研究。首先比较了3种分维模型所得孔隙分形维数的可靠性,然后选用热力学关系模型,由进汞、退汞试验得到地裂缝区黄土、充填黄土初始样和三轴应力路径试验后的孔隙分布,据此分析了两种土体进汞孔隙和退汞孔隙分形维数的差异和受载后的分形维数变化,根据退汞过程仅管形孔内的汞流出及孔隙由管形孔和球形孔组成的假定,得到了应力路径试验前后孔隙形状的改变。结果表明,热力学关系模型得到的孔隙分形维数合理、可靠。初始状态,原状和重塑充填黄土的孔隙形状比原状和重塑黄土复杂;常规三轴试验后试样孔隙比减少,孔隙分形维数增加,球形孔向管形孔转变;相对于常规三轴压缩试验,减围压三轴压缩试验后试样的孔隙分形维数较小,管形孔占总孔隙的体积比例较少;总体上管形孔的分形维数比球形孔大,且基本不受应力路径的影响,其占总孔隙的体积比例随着试样宏观孔隙比的减少而增加。 相似文献