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静止土压力系数(K0)是岩土工程中计算侧向土压力的关键参数,原状和重塑黄土的K0系数在固结过程中的发展规律明显区别于黏土或砂土。为研究围压和初始孔隙比对原状和重塑黄土的K0系数的影响,采用加装高精度局部径向位移计(LVDT)的应力路径三轴仪开展了K0固结试验研究,结果表明:(1)重塑黄土的K0系数受初始孔隙比(e0)的影响较为明显,当试样的初始孔隙比减小(从0.775变为0.503),其K0系数的最大降幅为55%;然而原状黄土的K0系数受有效围压(σ3′)的影响较为明显,比如在σ3′ < 350kPa时,K0系数为0.77~0.85,在σ3′>350kPa时,K0系数为0.46~0.51;(2)在固结过程中,原状黄土试样和重塑黄土试样的K0系数均发生陡降,具体表现为重塑黄土密样(e0<0.6)的陡降发生在固结的起始阶段,重塑黄土松样(e0 ≈ 0.77)的陡降发生在有效围压接近100kPa,而原状黄土试样的陡降发生在有效围压为350kPa附近;(3)在相同的有效围压和密度条件下,原状黄土的K0系数大于重塑黄土。采用核磁共振技术(NMR)获取了重塑和原状黄土的孔隙分布,并辅以试样的超孔隙水压力、排水体积等数据进行了讨论,发现结构性是造成黄土K0系数差异的主要原因。 相似文献
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本文利用扁铲侧胀试验对超固结砂土的土力学参数进行测试,目的是获取砂土的超固结比OCR和静止土压力系数k_0。经过一系列室内试验箱砂土物理模型试验的精确测试,分别得到在加载和卸载阶段的P_0压力值和P_1压力值,并换算成各项扁铲侧胀试验指标。试验结果表明,在扁铲侧胀试验指标中,侧胀水平应力指数K_D更能反映粗颗粒砂土的超固结比,因此,可用相对密实度D_r和侧胀水平应力指数K_D建立超固结比OCR的表达式;由于K_D/k_0和E_D/σ'_m之间有共同的因子,即状态参数ψ,因此可建立两者的关系式来计算静止土压力系数k_0。 相似文献
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静止土压力系数K0描述土体的原位应力状态,是许多工程计算的重要参数。本文通过等应变速率K0固结试验,研究原状和重塑马兰黄土的K0变化规律,并探讨这种变化与内部结构的关系。结果表明:(1)原状和重塑马兰黄土的K0均不是恒定值,根据土体结构的变化,其固结过程可分为初始阶段和稳定阶段。初始阶段K0(以K0i表示)随含水率的增加呈线性增长,稳定阶段K0(以K0s表示)随含水率的增加呈双曲线增长,且K0s始终大于K0i。(2)原状马兰黄土的K0i小于重塑马兰黄土,原因在于原状马兰黄土具有很强的簇聚结构,这种竖向结构弱化了水平应力的增长;而重塑马兰黄土趋于均质,呈各向同性,进而导致较高的K0i。(3)稳定阶段,原状马兰黄土的初始结构被破坏,与重塑马兰黄土近似,使得两者的K0s相近。(4)相较于其他类土,原状马兰黄土的K0s始终呈现较小值(饱和原状马兰黄土的K0s基本稳定在0.45左右,而其他类土可高达0.8)。通过对不同K0下的边坡进行数值模拟,发现低K0土体更易于在坡顶区域形成近直立的深长拉张裂隙,这也是典型黄土地貌(如黄土墙、黄土柱)形成的重要原因之一。 相似文献
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欠固结土是在自重作用下尚未固结完成的土,欠固结土的超固结比（overconsolidation ratio,简称OCR）取值在现有文献中可见两种不同的表述,分别是等于1和小于1,这容易导致概念混淆和超固结比取值误用等问题。对国内外使用较为广泛的土力学教材中超固结比相关内容进行了整理,发现超固结比有两种不同的定义表达式,这两种表达式中分母的不同是导致欠固结土超固结比取值差异的根源。采用知识图谱法,对超固结比和欠固结土的概念内涵、历史源头和研究应用等进行了综合分析,结果表明：研究欠固结土相关问题时,采用固结度或固结状态参数作为分析变量可完全替代超固结比的作用;将超固结比定义为前期固结应力与现有有效应力的比值（即OCR = pc /p′0,pc为前期有效固结压力,p′0为竖直有效应力）,契合应力历史对土体工程特性影响的内在机制,也符合概念的历史渊源。 相似文献
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本文借助于先进的多功能大型高速高压环剪试验机,通过进行不同应力历史、剪切速度和正应力等条件下的系列试验,对吉林长春地区广泛分布的超固结粉质黏土在快速大剪切位移条件下的力学响应特性进行了试验研究。试验结果显示,前期固结历史和剪切速度不仅对超固结粉质黏土的抗剪强度变化具有显著的影响作用,并且对于其峰后应变软化亦产生明显的影响。在相同剪切速率和正应力条件下,前期固结压力越大,其峰值强度和残余强度值越大。不同剪切速度下的试验结果表明,在具有相同应力历史的条件下,峰值强度和峰后应力降低随着剪切速度的增大而增大。剪切速度越快越有利于土应变软化的产生以及剪切面的形成。在快速大剪切条件下对长春地区超固结粉质黏土抗剪强度变化起主要作用的是剪切过程中土体结构的变化和剪切面的生成,而剪切过程中孔隙水的作用并不显著。 相似文献
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《岩土力学》2017,(4)
通过应力路径三轴试验对不同超固结比下饱和软黏土的K_0系数及K_0超固结软土的抗剪强度进行了研究,提出了超固结软土的K_0系数计算公式,基于各向异性屈服准则推导了K_0超固结软黏土的不排水抗剪强度,并与试验结果对比证明了计算公式的有效性。分析表明,常用的Mayne-Kulhawy K_0系数计算公式过高地估算较大超固结比OCR时的K_0系数,同时所提出的K_0超固结软黏土不排水抗剪强度公式通过考虑土体K_0系数随OCR的变化,避免了假设以有效上覆压力表示的回弹线斜率为常数所存在的问题。通过与试验结果对比表明,该公式能较好地预测K_0超固结土体的不排水抗剪强度。 相似文献
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针对长江口地区的重塑饱和海洋黏土,进行了一系列均等固结条件下的应力控制式轴向-扭转双向耦合循环剪切试验,着重探讨了循环荷载分量比R与超固结比OCR对孔压与动强度特性的影响。试验结果表明,随着R的减小,波动孔压幅值逐渐降低,而残余孔压先降低后升高,R = 1时残余孔压最小。在循环耦合剪切作用过程中,对应相同循环次数,随着OCR的增大,累积孔压变小,而波动孔压幅值却在增大。对应相同循环次数比N/Nf,随着OCR增大,残余孔隙水压力比ur / urmax减小。经归一化处理后ur / urmax-N/Nf关系曲线对于正常固结与超固结饱和黏土可分别用不同的表达式来表达。随着R的降低,破坏循环次数先增大后减小,R = 1时最大。随着OCR的增大,饱和黏土的强度变化减小 相似文献
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大量工程实践表明：正确预估欠固结地层的静止侧压力大小对工程的稳定性分析和安全设计十分重要。因此,通过理论分析和数值模拟深入探讨了固结排水过程中地层侧向压力的变化规律,建立了静止侧压力与超固结比OCR的联系,提出了等效静止土压力系数的概念和计算公式,形成了考虑OCR影响的欠固结地层静止侧压力简化计算方法,并用数值模拟和试验结果进行了验证。提出的等效静止土压力系数实现了欠固结地层和正常固结地层侧压力计算的统一。研究结果表明：欠固结地层的静止侧压力随超固结比OCR的增大而线性减小,且随土体有效内摩擦角的增大,OCR对侧向压力的影响越大。上述研究成果可为欠固结地层的土压力计算提供技术支撑。 相似文献
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Emily Keeble David I. Whiteside Michael J. Benton 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(2):99-119
Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco. 相似文献
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Gilles Serge Odin 《Comptes Rendus Geoscience》2002,334(6):409-414
Lithostratigraphy, physicochemical stratigraphy, biostratigraphy, and geochronology of the 77–70 Ma old series bracketing the Campanian–Maastrichtian boundary have been investigated by 70 experts. For the first time, direct relationships between macro- and microfossils have been established, as well as direct and indirect relationships between chemo-physical and biostratigraphical tools. A combination of criteria for selecting the boundary level, duration estimates, uncertainties on durations and on the location of biohorizons have been considered; new chronostratigraphic units are proposed. The geological site at Tercis is accepted by the Commission on Stratigraphy as the international reference for the stratigraphy of the studied interval. To cite this article: G.S. Odin, C. R. Geoscience 334 (2002) 409–414. 相似文献
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The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts 总被引：4，自引：0，他引：4
The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H2O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H2O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species. 相似文献
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Muriel Rocher Stéphane Baize Stéphane Jaillet Edward Marc Cushing Yannick Lozac&#x;h Francis Lemeille 《Comptes Rendus Geoscience》2003,335(8):701-708
Calcite samples were extracted both from the rock matrix and the superficial coating of a karstified fault plane of an underground quarry, located in the eastern border of the Paris basin. The karstification is dated as Quaternary. Analysis of mechanical calcite twinning reveals that only the calcite matrix has also undergone a compression trending WNW that can be attributed to the Mio-Pliocene alpine collision. Both coating and matrix have undergone a strike-slip regime with σ1 roughly trending north–south, that could correspond to the regional present-day state of stress, a strike-slip compression rather trending NNW, modified by local phenomena. To cite this article: M. Rocher et al., C. R. Geoscience 335 (2003). 相似文献
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正20141520 Bo Ying(Key Laboratory of Metallogeny and Mineral Assessment,MLR,Beijing 100037,China);Liu Chenglin Saline Spring Hydrochemical Characteristics and Indicators for Potassium Exploration in Southwestern and Northern Tarim Basin,Xinjiang(Acta Geoscientica Sinica,ISSN1006-3021,CN11-3474/P,34(5),2013,p.594-602,5 illus.,3 tables,28 refs.) 相似文献
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正20141243Chen Ge(Hangzhou Research Institute of Petroleum Geology,PetroChina,Hangzhou 310023,China);Si Chunsong Study on Sedimentary Numerical Simulation Method of Fan Delta Sand Body(Journal of Geology, 相似文献
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正20142599Chen Sanming(Guangxi Key Laboratory of Concealed Deposits Exploration,Guilin University of Technology,Guilin541004,China);He Yuzhou Block Model and Reserves Estimation of Panzhihua Iron Deposit Based on 3D Geological Modeling(Journal of Guilin University of Technology,ISSN1674-9057,CN45-1375/N,33(4),2013,p.610-615,9illus.,1table,15refs.) 相似文献
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正20140594 Bai Daoyuan(Hunan Institute of Geology Survey,Changsha 410016,China);Zhong Xiang Faults in the Jingzhou Basin and Their Tectonic Settings(Geotectonica et Metallogenia,ISSN1001-1552,CN44-1595/P,37(2),2013,p.173-183,6illus.,59refs.)Key words:basin evolution,tectonic setting,South China In the Upper Paleozoic and Jurassic se- 相似文献
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正20141912Cao Hui(State Key Laboratory for Continental Tectonics and Dynamics,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)Gravitational Collapse and Folding during Orogenesis:A Comparative Study of FIA Trends and Fold Axial Plane Traces(Geology in China,ISSN1000-3657,CN11-1167/P,40(6),2013,p.1818-1828,9illus.,35refs.,with 相似文献