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31.
32.
In urban environments, one major concern with deep excavations in soft clay is the potentially large ground deformations in and around the excavation. Excessive movements can damage adjacent buildings and utilities. There are many uncertainties associated with the calculation of the ultimate or serviceability performance of a braced excavation system. These include the variabilities of the loadings, geotechnical soil properties, and engineering and geometrical properties of the wall. A risk‐based approach to serviceability performance failure is necessary to incorporate systematically the uncertainties associated with the various design parameters. This paper demonstrates the use of an integrated neural network–reliability method to assess the risk of serviceability failure through the calculation of the reliability index. By first performing a series of parametric studies using the finite element method and then approximating the non‐linear limit state surface (the boundary separating the safe and ‘failure’ domains) through a neural network model, the reliability index can be determined with the aid of a spreadsheet. Two illustrative examples are presented to show how the serviceability performance for braced excavation problems can be assessed using the reliability index. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
33.
The gray crystalline hematite at Meridiani Planum first discovered by the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) instrument occurs as spherules that have been interpreted as concretions. Analysis of the TES and mini-TES spectra shows that no 390 cm−1 feature is present in the characteristic martian hematite spectrum. Here, we incorporate the mid-IR optical constants of hematite into a simple Fresnel reflectance model to understand the effect of emission angle and crystal morphology on the presence or absence of the 390 cm−1 feature in an IR hematite spectrum. Based on the results we offer two models for the internal structure of the martian hematite spherules. 相似文献
34.
Håkon Austrheim Christine V. Putnis Ane K. Engvik Andrew Putnis 《Contributions to Mineralogy and Petrology》2008,156(4):517-527
Ilmenite in coronitic gabbros from the Bamble and Kongsberg sectors, southern Norway, is surrounded by zircons ranging in
diameters from a fraction of a micrometer to 10 μm across. The zircons are inert during subsequent metamorphism (amphibolite-
to pumpellyite–prehnite facies) and metasomatism (scapolitization and albitization) and can be found as trails in silicates
(phlogopite, talc, chlorite, amphibole, albite, and tourmaline) in the altered rocks. The trails link up to form polygons
outlining the former oxide grain boundary. This 3-dimensional framework of zircons is used to (a) recognize metasomatic origin
of rocks, (b) quantify the mobility of elements during mineral replacement, (c) establish the growth direction of reaction
fronts and to identify the reaction mechanism as dissolution–reprecipitation. Zircon coronas on Fe–Ti oxides have been described
from a number of terrains and appear to be common in mafic rocks (gabbros and granulites) providing a tool for a better understanding
of metasomatic and metamorphic reactions. 相似文献
35.
Influence of Structural Non-Stationarity of Surface Roughness on Morphological Characterization and Mechanical Deformation of Rock Joints 总被引:2,自引:2,他引:0
N. Fardin 《Rock Mechanics and Rock Engineering》2008,41(2):267-297
Summary Structural non-stationarity of surface roughness affects accurate morphological characterization as well as mechanical behaviour
of rock joints at the laboratory scale using samples with a size below the stationarity threshold. In this paper, the effect
of structural non-stationarity of surface roughness is investigated by studying the scale dependence of surface roughness
and mechanical behaviour of rock joints. The results show that the structural non-stationarity mainly affects the accurate
characterization of the surface roughness of the fracture samples. It also controls the amount and location of the contact
areas during shear tests, which in turn affects the mechanical properties and asperity degradation of the samples. It is concluded
that for accurate determination of the morphological and mechanical properties of rock joints at laboratory and field scales,
samples with size equal to or larger than the stationarity threshold are required.
Author’s address: Nader Fardin, Rock Mechanics Group, Department of Mining Engineering, Faculty of Engineering, University
of Tehran, P.O. Box: 11365/4563, Tehran, Iran 相似文献
36.
本文以赤道东太平洋海温作为主导因子,分析其与东亚温带气旋的关系。得出:高海温多气旋,低海温少气旋的对应关系较为明显。并进一步对不符合这种主要关系的年份从环流型。下垫面海温等作了分类鉴别分析。 相似文献
37.
物质海 -气通量计算新建议中将物质海 -气通量计算公式 F=K(CL- b Cg)中的 CL 用CL ( SML ) 代替。本文着重于对公式中质量迁移系数 K的讨论。在测定了海水微表层、次表层水粘度并同时测定了其它一些化学参量基础上 ,得出如下结论 :海水粘度与盐度、碱度有一定相关性 ;微表层与次表层海水的粘度变化小于 3%。因此 ,海水微表层效应影响 K值 ,与海水微表层效应影响物质浓度相比 ,可以不考虑。 相似文献
38.
39.
太平洋东南海域表层地转流场的季节及年际变化特征 总被引:1,自引:0,他引:1
利用1992~2001年Topex/Poseidon卫星高度计遥感资料分析了太平洋东南海域(5°~55°S,70°~120°W)表层流场的季节及年际变化特征。结果表明,南赤道流的季节变化主要体现在流速上,而秘鲁海流和西风漂流主要体现在流轴位置的移动上。表层流场的年际变化受El Nino影响,在El Nino期间,南赤道流和秘鲁海流均发生流向偏转现象,大部分海区流场被削弱(除低纬度海区外),而在其后的1998年La Nina期间,流场则重新被加强,西风漂流无明显的年际变化。 相似文献
40.