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One‐dimensional dynamics of saturated incompressible porous media: analytical solutions and influence of inertia terms 
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下载免费PDF全文 The complexity of formulations for the hydromechanical coupled mechanics of porous media is typically minimised by simplifying assumptions such as neglecting the effect of inertia terms. For example, three formulations commonly employed to model practical problems are classified as fully dynamic, simplified dynamic and quasi‐static. Thus, depending on the porous media conditions, each formulation will have advantages and limitations. This paper presents a comprehensive analysis of these limitations when solving one‐dimensional fully saturated porous media problems in addition to a new solution that considers a more general loading situation. A phase diagram is developed to assist on the selection of which formulation is more appropriate and convenient regarding particular cases of porosity and hydraulic conductivity values. Non‐dimensional formulations are proposed to achieve this goal. Results using the analytical solutions are compared against numerical values obtained with the finite element method, and the effect of porosity is investigated. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Uptake of the trace metals, Pd, Cd, Hg and Pb, by the marine macroalga, Ulva lactuca, has been studied along a salinity gradient (S = 15–35; pH ~ 8.3) created by batch mixing of synthetic sea water and pure water, both in the absence and presence of humic substances. Factors defining the concentration ratio of metal taken up (w/w) to metal remaining in solution ranged from about 102 mL g− 1 for Cd to 103 mL g− 1 for Pd and Hg. Within experimental error, only the biouptake of Cd appeared to exhibit a dependence on salinity, while the addition of 3 mg L− 1 of humics resulted in a small suppression of Pd and Hg uptake and a moderate enhancement of Pb uptake compared with the humic-free system. Metal internalisation, evaluated from an EDTA wash of the alga, followed the sequence: Hg > Pd > Cd > Pb; and was notably inhibited in the presence of humics for Pb. Metal uptake (as adsorption and internalisation) was modelled using the Windermere Humic Aqueous Model (WHAM, v6) by encoding the macroalga as a polyelectrolytic binding phase whose properties were defaulted to those of aqueous humics in the software database. By setting the “activity” of the binding phase to about 0.1 and systematically reducing the default constants for metal binding, the magnitude of metal uptake by U. lactuca was reproduced. However, for all metals the model predicted a reduction in algal uptake as a function of salinity that was not always observed experimentally. Moreover, calculations performed in the presence of aqueous humic substances and using the earlier fitted constants significantly underestimated metal uptake by U. lactuca. Discrepancies between experimental observations and model calculations, which are attributed to the formation of ternary complexes at the algal surface, suggest that conventional equilibrium speciation considerations alone are not applicable for modelling metal interactions with marine macroalgae. 相似文献
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Tun Ye W. Llano-Serna Marcelo A. Pedroso Dorival M. Scheuermann Alexander 《Acta Geotechnica》2019,14(1):207-223
Acta Geotechnica - This paper presents a genetic algorithm (GA) to solve the multimodal optimisation problem resulting from 3D slopes prone to multiple regions of failure. A probabilistic approach... 相似文献
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An automatic technique for the determination of the coefficients of models for soil–water characteristic curves (SWCC) or water retention curves (WRC) is presented. The technique is based on optimisation using genetic algorithms, in which the error between predictions and experimental data is minimised by varying the model parameters. The method is powerful and reasonably efficient in finding the best parameters. Four models are analysed including one accounting for hysteresis behaviour. Details of a simple genetic algorithm (SGA) and its complete application are explained. To account for the hysteresis of the SWCC, the models are programmed in a rate form, in which numerical integration is employed to advance the state variables. One advantage of the optimisation presented is that the best curves averaging both the drying and wetting paths are obtained when hysteresis is present. 相似文献
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This paper presents a simple concept which can be used for simulating a range of soil mechanics problems. The study is motivated by the observation that many experimental results are commonly described in terms of lines or curves according to a phenomenological approach. Frequently, these relations are based on rather different formulations from one application to another, and in complex forms for some cases. This leads to complications for the calibration of parameters as well as constitutive modelling. Thus, a general framework referred to as “reference curves” has been developed. This framework provides a unique treatment of the macroscopically observed behaviour of clays, sands, and structured materials under isotropic compression, as well as the water retention characteristics of granular materials and geotextiles. Several examples are provided illustrating the good accuracy of models developed with this concept. The proposed framework may be equally applied to any other behaviour where reference lines are easily identifiable from a macroscopic scope, such as some non-linear failure envelopes for granular materials. In addition, we show that the incorporation of the proposed equations into constitutive models is quite straightforward. 相似文献
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This paper discusses the numerical integration of the subloading tij model. This is an elastoplastic model with stress path dependent hardening, which can predict the behaviour of normally consolidated clays or loose sands, as well as of over-consolidated clays or dense sands, with a small number of material parameters. Three features distinguish the subloading tij model from the conventional ones: (a) the use of a modified stress space given by tensor tij; (b) the split of the plastic strain increments in two components leading to a stress path dependent hardening; and (c) the use of two yield surfaces (subloading yield surface and normal yield surface). This last feature is based on the concept of sub-yielding stress states and adds an extra internal strain-like hardening variable, related to the relative density state, which demands its own evolution law. The three characteristics above greatly improve the prediction capabilities of the model, with respect to those of the well-known Cam clay model, at the cost of only two additional parameters. Nonetheless, the numerical integration of the constitutive equations of subloading tij model is a bit challenging, mainly due to the stress path dependent hardening. In order to integrate the equations of subloading tij model in the same way as for any conventional model, the authors reformulated its equations in a simpler and direct manner. Here, these equations are integrated using multi-step explicit schemes, such as modified-Euler and Runge–Kutta–Dormand–Price, with automatic error control. Simple forward-Euler scheme is also used for the sake of comparison. The results show that the modified-Euler scheme is more accurate as well as faster than the other schemes analysed over a wide range of error tolerance. Besides, the automatic feature of these schemes is a great convenience for the users of numerical codes. 相似文献
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An assessment of the material point method for modelling large scale run-out processes in landslides 总被引：1，自引：1，他引：0
This paper demonstrates the predictive capabilities of a numerical model based on continuum mechanics for the simulation of run-out processes during landslides. It assesses a particle-based method that takes advantage of a double Lagrangian-Eulerian discretization and known as the material point method (MPM). Attention is given to the post-failure behaviour and, in particular, to the computation of important quantities such as run-out distance, maximum velocity and energy release. The MPM is a step forward in computational solid mechanics and has the potential to simulate large deformations such as those occurring during landslides. A validation is conducted based on simulations of two case studies of different scales, namely the Tokai-Hokuriku expressway failure in Japan and the Vajont landslide in Italy. The results show a very good agreement with field and other numerical observations. 相似文献
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Zhang Yunpeng Pedroso Dorival M. Li Ling Scheuermann Alexander Ehlers Wolfgang 《Acta Geotechnica》2020,15(7):1859-1879
Acta Geotechnica - When applying equal-order monolithic schemes for the solution of incompressible fluid saturated porous media dynamics, the resulting pressure field often exhibit spurious... 相似文献
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The Barcelona Basic Model (BBM) is an extension of the Cam clay model that has become popular in applications involving unsaturated soils and, in particular, in simulations using the finite element method. Partially saturated soils can be loaded in different ways, for instance, mechanically and/or hydraulically. In addition, cycles of loading and unloading can be applied. The present work introduces a modification of the BBM in order to simplify its computer implementation and also to allow the simulation of elastoplastic behaviour during cycles of both mechanical and hydraulic loading. A unique smooth yield surface is introduced and a two-yield surfaces concept is applied in order to represent the cyclic behaviour. The influence of the intermediate principal stress on the strength is also accounted for. Finally, the numerical integration (stress update) of the extended BBM is briefly discussed. 相似文献
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Soil–water characteristic curves can be defined as the relationship between the degree of saturation and suction of an unsaturated soil. Geomaterials, such as clays, sands, and geotextiles, usually exhibit hysteresis between drying and wetting curves. In addition, each drying and wetting curve is nonlinear in shape, which may be approximated by sigmoid curves. In geotechnical engineering, it is common to adopt analytical expressions for these curves that must be calibrated iteratively by trying different values for the constitutive parameters. In this paper, a novel approach for modelling the nonlinear saturation–suction response with hysteresis is presented, where a simple differential equation is introduced to describe the shapes of the curves. The great advantage of this new technique is the ease with which the parameters can be determined. In addition, the implementation of the resulting equations into fully hydro-mechanical models for numerical analyses is straightforward. Some features of the behaviour predicted with the new representation are studied and validations against real laboratory curves for soils are presented. The technique is simple, yet versatile due to the rational basis used in the deduction of the equations, which allows for future extensions to soils displaying more complex unsaturated behaviour. 相似文献
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