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In order to provide a physical interpretation of the variation of the mechanical properties of Callovo-Oxfordian argillite with mineral composition, we implement three linear homogenization schemes. The argillite is modeled as a three phase material composed of a clay matrix and inclusions of quartz and calcite. It is shown that, unlike the dilute scheme and the self-consistent scheme, the Mori-Tanaka model describes the in situ experimental data well. The determined properties are finally used in a finite element computation. The aim is to evaluate the effect of mineral composition on the elastic response of the excavation of a vertical shaft in the context of the underground laboratory of Meuse/Haute Marne. 相似文献
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A multiphase model, developed in the context of elastoplasticity, is applied to the simulation and design of reinforced earth retaining structures. The main feature of this model is to combine the advantage of a homogenization approach, as regards its computational efficiency, with the ability to account for a specific failure condition at the interface between the soil and the reinforcing strips, which may have a decisive influence on the behavior of the structure. A particular emphasis is put on the stability analysis of this kind of reinforced soil structures, formulated within the framework of the yield design theory. Making use of a generalized rigid block failure mechanism, the stability of a reinforced earth retaining wall is investigated by means of the kinematic approach, leading to upper bound estimates for the stability factor of the structure, which are then favorably compared with the results of an elastoplastic analysis. Special attention is paid to assessing in a quantitative way how a specific soil–strip failure condition affects the stability of the reinforced earth structure as a whole. 相似文献
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青海茶卡盐湖石盐中流体包裹体记录的古气候信息 总被引：3，自引：0，他引：3
内陆干旱区形成的盐湖是研究过去气候变化的有效载体之一,而石盐中包裹体是揭示古气候的一种有效手段。青海茶卡盐湖是晚更新世晚期,逐渐演变形成的以石盐为主,固液相并存的综合性盐矿床。对茶卡盐湖钻孔样品中石盐的流体包裹体均一温度研究,揭示出从5ka 以来,盐湖水温总体上逐渐升高,从20℃～30℃升高到接近400℃,反映出古气候的温度是逐渐升高的,与全球变暖的总体趋势是一致的。研究表明,对石盐中原生单液相流体包裹体,采用冷冻-加热的方法测定均一温度,是获得盐湖古水温资料,进而恢复古气候变化的一种十分可信新手段,它在盐湖的研究方面具有广阔的应用前景。 相似文献
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This paper addresses the question of how spatial variability in the hydraulic and chemical properties of groundwater systems affects the transport and sorption behavior of pollutants at the field scale. In this paper, we limit our investigations on pollutants that adsorb according to an equilibrium controlled nonlinear Freundlich sorption isotherm. The new contribution of this paper is take into account not only spatially variable Freundlich distribution coefficients KS but spatially variable Freundlich nonlinearity parameters p as well. Using a homogenization theory approach, we shortly review the impact of spatially variable hydraulic properties on the transport and extend the theory to spatially variable chemical properties. We show that spatially variable Freundlich exponents cause a very different field scale transport and sorption behavior than spatial variations in the distribution coefficients only since in the first case field scale Freundlich parameters and field scale dispersion coefficients become concentration dependent. In particular, field scale retardation is much larger than small-scale retardation. 相似文献
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基于国家气象信息中心"基础气象资料建设专项"研制的中国地面历史基础气象资料及台站元数据,利用RHtest V4软件包对天津1951~2012年的历史气温序列进行了均一性分析。结果显示,通过惩罚最大t检验(PMT)方法对12个地面站逐日平均、最高、最低气温序列检验得到,迁站是导致平均气温和最低气温序列突变的主要原因,同类型仪器更换则是导致最高气温序列突变的主要原因,而2005年以后的自动站业务化并没有对天津地区气温序列的均一性造成很大影响。同时,研究中也检验出少部分未知原因的显著间断点,可能是由于观测员的误判或观测仪器翘变等因素造成的历史数据疑误。从订正量来看,逐日平均气温和最高气温序列主要以正偏差订正为主,而最低气温则主要以负偏差订正为主。其中,最高气温序列的分位数匹配(QM)订正量均值最大,90%以上集中在0.1~1.0°C,平均气温序列的QM订正量均值相对最小,90%以上的订正量在-0.7~0.7°C,而最低气温的订正量90%以上集中在-1.5~1.5°C范围中。另外,以Xu et al.(2013)研制的数据集为参照,通过误差分析,发现两类研究得到的年(季节)尺度气温数据具有较高的相符率和一致性,从而可以说明本研究订正后的天津地区1951~2012年逐日气温序列具有一定的可靠性。 相似文献
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This paper presents a micromechanics-based elastoplastic damage model for quasi-brittle rocks under a compressive stress state. The plastic strain is considered to be related to frictional sliding along micro-cracks, and it is coupled inherently with damage evolution. By following a homogenization procedure, we determine the free energy of the matrix-cracks system. The thermodynamic force associated with the inelastic strain contains a back stress, which controls material hardening. Next, in order to determine plastic flow and crack propagation, we propose a Coulomb-type friction criterion, which is used as the plastic yielding function, and a damage criterion based on strain energy release rate. These thermodynamic formulations with a micro–macro scale change allow reducing significantly the number of model parameters, as compared to phenomenological models. Our model is applied to simulate triaxial compression tests on two sets of diabase samples. The first sample set is cored from a fresh diabase rock mass, and the second from a slightly weathered one. Comparisons between numerical predictions and test data are presented. 相似文献
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Density-dependent dispersion in heterogeneous porous media Part II: Comparison with nonlinear models 总被引：1，自引：0，他引：1
Anke Jannie Landman Ruud Schotting Andrey Egorov Denis Demidov 《Advances in water resources》2007,30(12):2481-2498
The results of a series of high-resolution numerical experiments are used to test and compare three nonlinear models for high-concentration-gradient dispersion. Gravity stable miscible displacement is considered. The first model, introduced by Hassanizadeh, is a modification of Fick’s law which involves a second-order term in the dispersive flux equation and an additional dispersion parameter β. The numerical experiments confirm the dependency of β on the flow rate. In addition, a dependency on travelled distance is observed. The model can successfully be applied to nearly homogeneous media (σ2 = 0.1), but additional fitting is required for more heterogeneous media.The second and third models are based on homogenization of the local scale equations describing density-dependent transport. Egorov considers media that are heterogeneous on the Darcy scale, whereas Demidov starts at the pore-scale level. Both approaches result in a macroscopic balance equation in which the dispersion coefficient is a function of the dimensionless density gradient. In addition, an expression for the concentration variance is derived. For small σ2, Egorov’s model predictions are in satisfactory agreement with the numerical experiments without the introduction of any new parameters. Demidov’s model involves an additional fitting parameter, but can be applied to more heterogeneous media as well. 相似文献