Solid–liquid–air coupling in multiphase porous media

This paper addresses various issues concerning the modelling of solid–liquid–air coupling in multiphase porous media with an application to unsaturated soils. General considerations based on thermodynamics permit the derivation and discussion of the general form of field equations; two cases are considered: a three phase porous material with solid, liquid and gas, and a two phase porous material with solid, liquid and empty space. Emphasis is placed on the presentation of differences in the formulation and on the role of the gas phase. The finite element method is used for the discrete approximation of the partial differential equations governing the problem. The two formulations are then analysed with respect to a documented drainage experiment carried out by the authors. The merits and shortcomings of the two approaches are shown. Copyright © 2003 John Wiley & Sons, Ltd.     

1970-2000年中国近地层大气热力增强的气候效应

中国区域1970-2000年622个气象观测台站资料EOF分析显示,气温的上升导致中国大部分地区饱和水汽压差呈上升趋势,大气热力强度增加,风动力明显减弱.内蒙中部以南至长江中游以北区域是大气热力增强最为敏感的地区.气温升高导致这一区域大气"干燥力"增强,区域蒸发潜力下降速度低于其他地区,气温的上升对低云覆盖产生一定程度...     

热力学方法在土体动力Ramberg—Osgood模型中的应用研究

从Ramberg—Osgood模型的骨架曲线和滞回曲线出发,假定塑性中心的移动为直线,构造土体动力耗散函数,从热力学基本定律出发研究了土体动力耗散特性及动力变形机理．提出了反映筑坝堆石料动力特性的第1阌值应变和第2阈值应变,两个阈值应变主要受最大动剪切模量系数、指数及无黏性土的内摩擦角的影响．第1和第2阈值应变间屈服面...     

Foreword

Protons of energy 10⁹ GeV and 10⁴ GeV accelerating by the magnetic field of very strongly magnetized neutron stars and of extreme Kerr-Newmann black holes (respectively) may undergo instantaneous decay.     

How well known are the thermodynamics of Fe–Mg–Ca garnet? Evidence from experimentally determined exchange equilibria

ABSTRACT Many thermodynamic calculations relating to metamorphic rocks hinge on the thermodynamic parameters of garnet. Though some models are widely used, it is not clear whether their underlying premise is correct: that a single set of equations can be written for the activities of the end-members of garnet covering the whole compositional range. A voluminous body of data can be used to constrain the thermodynamics of garnet, namely Fe–Mg exchange experimental data involving garnet and another mineral, particularly clinopyroxene, orthopyroxene and olivine. However, examination of these data reveals inconsistencies, apparently stemming from differences between the thermodynamics of low-Ca and high-Ca garnets, with a boundary of about X^g_Ca= 0.15. In the two regions, for the high P–T of the experimental data, the thermodynamics follow the regular model, with values for the interaction parameters in the low Ca region of about w^g_FeMg= 50R and w_aFe–w^g_MgCa=– 1300R, in which R is the gas constant, and in the high Ca region of about w^g_FeMg= 1100R and w^g_CaFe–w^g_MgCa=– 2200R. Using the subregular, rather than the regular, model does not remove the discrepancy. The cause of the discrepancy needs to be identified if reliable calculations on rocks are to be made.     

Application of thermodynamics to the global modelling of shallow foundations on frictional material

Soil–shallow foundation interaction has been theoretically analysed within the framework of thermomechanics. The design of a global interaction model has been achieved with an original treatment of the Clausius–Duhem inequality. The role of the gravity volume forces is emphasized. The paper is focused on a strip footing based on dense sand and subjected to time‐independent plastic processes. The theoretical approach has confirmed that an associated global flow rule cannot be expected to hold true. The analysis of the sources of dissipation has led to the development of a soil–footing interface model and a complete interaction model accounting for the interface constraints and the intrinsic frictional properties of the soil. Finally, the abilities of the complete model are checked by comparisons with experimental results found in the literature. Copyright © 2001 John Wiley & Sons, Ltd.     

A constitutive model based on modified mixture theory for unsaturated rocks

Non-equilibrium thermodynamics and Biot poro-elasticity have been combined to give a coupled hydro-mechanical formulation for unsaturated rock. Darcy’s law for unsaturated flow has been derived from the dissipation process by using standard arguments of non-equilibrium thermodynamics, whereas Helmholtz free energy has been used to derive the relationship between stress and pore pressure changes. The resulting general framework accommodates both large and small deformation theories. When small deformations are assumed, the formulation is comparable with coupled equations derived using an alternative approach. For illustrative purposes, the formulation has been used to analyse a seasonally affected tunnel model. Numerical results for the desaturation in winter and resaturation in summer, of the zone near the tunnel wall, have been evaluated and compared with the findings of other researchers.     

The truth and beauty of chemical potentials

This essay in honour of Mike Brown addresses aspects of chemical equilibrium and equilibration in rocks, with a focus on the role that chemical potentials play. Chemical equilibrium is achieved by diffusive flattening of chemical potential gradients. The idea of equilibration volume is developed, and the way equilibration volumes may evolve along a pressure–temperature path is discussed. The effect of the environment of an equilibration volume is key to understanding the evolution of the equilibration volume with changing conditions. The likely behaviour of equilibration volumes is used to suggest why preservation of equilibrium mineral assemblages and mineral compositions from metamorphism tends to occur. This line of logic then provides the conceptual support to conventional equilibrium thermodynamic approaches to studying rocks, using, for example, thermobarometry and pseudosections.     

岩土流动势的存在性及解耦性

基于不可逆热力学岩土损伤理论的流动势理论存在两个基本问题：（1）岩土材料是否存在流动势;（2）流动势可否分解为塑性势和损伤势,即塑性、损伤两种机制可否解耦,给出了流动势存在的充分必要条件并加以严格证明,结合岩土的基本变形性质,证明了岩土不存在流动势。进一步考察流动势的解耦性,给出了流动势的塑性流动与损伤流动可解耦的充分必要条件,并进行了严格论证,结合土体的基本变形性质,证明了岩土塑性流动和损伤流动机制不可解耦,从而也为其他固体材料流动势的存在性和解耦性提供判别依据。