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21.
Takashi Yoshino 《Comptes Rendus Geoscience》2019,351(2-3):171-181
The core–mantle boundary is the only interface where the metallic core and the silicate mantle interact physically and chemically. Many geophysical anomalies such as low shear velocity and high electrical conductivity have been observed at the bottom of the mantle. Perturbations in the Earth's rotation rate at decadal time periods require the existence of a thin conductive layer with a conductance of 108 S. Substantial additions of molten iron from the outer core into the mantle may produce these geophysical anomalies. Although iron enrichment by penetration has only been observed in (Mg,Fe)O, the second dominant mineral in the lower mantle, the penetration process leading to iron enrichment in the silicate mantle has not been experimentally confirmed. In this study, high-pressure and high-temperature experiments were conducted to investigate the penetration of molten iron alloy into lower mantle phases; postspinel, polycrystalline bridgmanite and polycrystalline (Mg,Fe)O. At the interface between (Mg,Fe)O aggregate and molten iron alloy, liquid metal penetrated the (Mg,Fe)O aggregate along grain boundaries and formed a thin layer containing metal-rich blobs. In contrast, no penetration of molten iron alloy was observed at the interface between molten iron alloy and silicate phases. Penetration of liquid iron alloy into the (Mg,Fe)O aggregate is caused by the capillarity phenomenon or Mullins–Sekerka instability. Neither mechanism occurs at the boundary of pure polycrystalline MgO, indicating that the FeO in (Mg,Fe)O plays an essential role in this phenomenon. Infiltration of molten iron alloy along grain boundaries (capillarity phenomenon) is the dominant process and precedes penetration due to the Mullins–Sekerka instability. The capillarity phenomenon is governed by the balance of forces between surface tension and gravity. In the case where the ultralow velocity zone (ULVZ) with a low shear velocity is composed of Fe-rich (Mg,Fe)O, the maximum penetration distance of molten iron alloy by capillary rise is limited to 20 m. The addition of iron-rich melt to the base of the mantle is therefore unlikely to be the main cause of the high conductance of the CMB region predicted from decadal variation of the length of day. Furthermore, the absence of molten iron alloy penetration into silicate phases does not allow an extensive modification of the chemical composition of the mantle by core–mantle interaction. 相似文献
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The paper presents total-stress numerical analyses of large-displacement soil-structure interaction problems in geomechanics using the Particle Finite Element Method (PFEM). This method is characterized by frequent remeshing and the use of low order finite elements to evaluate the solution. Several important features of the method are: (i) a mixed formulation (displacement-mean pressure) stabilized numerically to alleviate the volumetric locking effects that are characteristic of low order elements when the medium is incompressible, (ii) a penalty method to prescribe the contact constraints between a rigid body and a deformable media combined with an implicit scheme to solve the tangential contact constraint, (iii) an explicit algorithm with adaptive substepping and correction of the yield surface drift to integrate the finite-strain multiplicative elasto-plastic constitutive relationship, and (iv) the mapping schemes to transfer information between successive discretizations. The performance of the method is demonstrated by several numerical examples, of increasing complexity, ranging from the insertion of a rigid strip footing to a rough cone penetration test. It is shown that the proposed method requires fewer computational resources than other numerical approaches addressing the same type of problems. 相似文献
23.
采用等效渗透系数法搜索渗流自由面 总被引:5,自引:1,他引:4
采用一个具体的实例对比分析了当前最为常用的几种自由面确定方法 ,阐明了各自的优缺点 ;然后在此基础上对单元传导矩阵调整法作了简化和改进 ,提出了等效渗透系数法。应用表明 ,等效渗透系数法不仅具有足够的计算精度 ,而且还具备算法简单、易推广等优点 相似文献
24.
静力触探(CPT)是一种速度快,数据连续、再现性好、操作省力等优点的原位测试方法。随着海洋开发的迅速发展,CPT测试技术在国内外海洋工程领域的使用越来越普遍。因此,了解国外海上CPT设备和应用情况,探讨应用中的问题,对CPT测试技术在我国海上工程领域的应用具有重要意义。文章描述了国外海上静力触探(CPT)测试技术的发展现状,阐明了主要的海床CPT(Seabed CPT)设备和井下CPT(Downhole CPT)设备的特点,并对不同CPT设备在海洋工程领域的应用作了分析,这对海上CPT测试技术在我国的应用和发展具有一定的参考价值和指导作用。 相似文献
25.
通过对镇江开发区某工程振动沉管桩基础施工方法的总结,系统地论述了沉管灌注桩施工中发生缩径的原因,提出了预防措施。 相似文献
26.
研究土体结构强度对了解土体开裂破坏过程和预防相关工程地质问题有重要意义。以南京地区下蜀土为对象,采用超微型贯入试验方法,分析了试样在干燥过程中的结构强度演化特征。结果表明:所采用的超微型贯入试验方法为定量研究土体在干燥过程中结构强度的演化规律提供了可行的途径,该方法具有操作简单、精度高和含水率适应范围大等优点; 在干燥过程中,当试样处于高含水率阶段时(w24.27%),剖面上的结构强度基本保持一致,空间差异性较小; 在低含水率阶段(w24.27%),试样结构强度空间差异性显著增强,随深度的增加,结构强度呈递减趋势并逐渐趋于稳定; 总体上,土体的结构强度在干燥过程中随平均含水率的减小呈指数递增趋势,这主要是由于土体水分蒸发导致吸力增加,土颗粒之间的作用力增强。此外,由于土体发生收缩变形,土体孔隙比减小,土颗粒间联接点增加,也会对结构强度产生贡献。 相似文献
27.
Hanna Hadler Andreas Vött Timo Willershäuser Dennis Wilken Ruth Blankenfeldt Claus von Carnap-Bornheim Kurt Emde Peter Fischer Ulf Ickerodt Stefanie Klooß Bente Majchczack Lea Obrocki Wolfgang Rabbel 《地球表面变化过程与地形》2021,46(15):3228-3251
In ad 1362, a major storm surge drowned wide areas of cultivated medieval marshland along the north-western coast of Germany and turned them into tidal flats. This study presents a new methodological approach for the reconstruction of changing coastal landscapes developed from a study site in the Wadden Sea of North Frisia. Initially, we deciphered long-term as well as event-related short-term geomorphological changes, using a geoscientific standard approach of vibracoring, analyses of sedimentary, geochemical and microfaunal palaeoenvironmental parameters and radiocarbon dating. In a next step, Direct Push (DP)-based Cone Penetration Testing (CPT) and the Hydraulic Profiling Tool (HPT) were applied at vibracore locations to obtain in situ high-resolution stratigraphic data. In a last step, multivariate linear discriminant analysis (LDA) was successfully applied to efficiently identify different sedimentary facies (e.g., fossil marsh or tidal flat deposits) from the CPT and HPT test dataset, to map the facies' lateral distribution, also in comparison to reflection seismic measurements and test their potential to interpolate the borehole and CPT/HPT data. The training dataset acquired for the key site from coring and DP sensing finally allows an automated facies classification of CPT/HPT data obtained elsewhere within the study area. The new methodological approach allowed a detailed reconstruction of the local coastal landscape development in the interplay of natural marsh formation, medieval land reclamation and storm surge-related land losses. 相似文献
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