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1

Main drying and wetting curves of soils: on measurements, prediction and influence on wave propagation

Albers B.

Engineering Transactions

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2015

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Vol. 63, iss. 1

5--34

EN

Depending on the initial degree of saturation of a soil, different capillary pressure curves occur. If a sample is initially water saturated and then drained (process of drainage) the main drying curve results. On the other hand, if the sample is initially dry and water is supplied until saturation is reached (process of imbibition) the main wetting curve is the consequence. These two curves build a hysteresis loop. If after the first process the other is followed up (possibly a number of times), then inner hysteresis curves arise. The focus of this paper is the investigation of some aspects of the main drying curve (MDC) and the main wetting curve (MWC). Some methods of their measurement are discussed. Because of big differences in the capillary pressure for different degrees of saturation the measurement is laborious and time consuming and often application of more than one method is necessary. Consequently, often only the MDC is measured and the data is used to predict the MWC and inner curves. Exemplarily, one prediction method is shown and subsequently, for one soil type the resulting curves are used to calculate the wave speeds and attenuations of the appearing sound waves. The dependence of these wave features on frequency and saturation for the current example shows, that the hysteresis effect of the capillary pressure curve has only a slight effect on the propagation of sound waves in partially saturated sand.

2

BEM and FEM results of displacements in a poroelastic column

Albers B., Savidis S. A., Taşan H. E., von Estorff O., Gehlken M.

International Journal of Applied Mathematics and Computer Science

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2012

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Vol. 22, no. 4

883-896

EN

The dynamical investigation of two-component poroelastic media is important for practical applications. Analytic solution methods are often not available since they are too complicated for the complex governing sets of equations. For this reason, often some existing numerical methods are used. In this work results obtained with the finite element method are opposed to those obtained by Schanz using the boundary element method. Not only the influence of the number of elements and time steps on the simple example of a poroelastic column but also the impact of different values of the permeability coefficient is investigated.

3

Influence of coupling through porosity changes on the propagation of acoustic waves in linear poroelastic materials

Albers B., Wilmanski K.

Archives of Mechanics

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2006

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Vol. 58, nr 4-5

313-325

EN

In earlier works it has been shown that linearization of thermodynamical models of poroelastic materials yields a contribution to stresses in the form ......., where ... is the current porosity, ... denotes its value in the thermodynamical equilibrium and ... is a material parameter. It has been also claimed on the basis of rough estimates that this parameter gives only negligible contributions to the properties of acoustic waves. The purpose of this work is twofold. We investigate the influence of ß on the propagation of acoustic waves in more details. We use the full linear model of saturated poroelastic materials in which an additional coupling to porosity changes appears. This results from the presence of a term with the porosity gradient in the momentum sources. Such a model becomes identical with Biot's model without any added mass contribution in the limit if infinite relaxation time of porosity ... and for the parameters ß=0, and N=0, where the latter is describing the above mentioned influence of porosity gradient on the momentum sources. The analysis of influence of the parameter N, i.e. the influence of the porosity gradient on properties of acoustic waves, is the second purpose of this work. We also indicate a correction of the permeability contribution to the momentum source. The permeability coefficient ... is assumed in Biot's model to be dependent on the frequency. This is inconsistent with other temporal contributions to field equations. In order to obtain such a dependence in the Fourier space, one has to assume a viscous effect to enter the momentum source and we do so in the general equations. However, we do not use this general relation in the analysis of monochromatic waves.

4

Linear stability of a 1D flow in porous media under transversal disturbance with adsorption

Albers B.

Archives of Mechanics

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2002

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Vol. 54, nr 5-6

361-375

EN

In this paper we investigate the linear stability behavior of a flow within an adsorption/diffusion model for porous materials summarized in Section 2. We consider a 1D stationary flow through a poroelastic medium which is perturbed by transversal (2D) disturbances with mass exchange. The eigenvalue problem for the first step field equations is solved using a finite-difference scheme. We present the instability regions in dependence on the three most important model parameters, namely the bulk and surface permeability coefficients, and the mass density of the adsorbate on the inner surface.

5

Dependence of adsorption/diffusion processes in porous media on bulk and surface permeabilities

Albers B.

Archives of Mechanics

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2001

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Vol. 53, nr 4-5

289-306

EN

The paper contains a macroscopic continuum model for adsorption in porous materials (B. Albers [1, 2]) which is an extension of the model for porous bodies by K. Wilmański [7] on mass exchange processes. We consider the flow of a fluid/adsorbate mixture through channels of a solid component. The fluid serves as carrier for an adsorbate whose mass balance equation contains a source term. Due to low adsorbate concentration we deal with a physical adsorption process which means that particles of the adsorbate stick to the skeleton due to weak van der Waals forces. The model contains two different permeability parameters whose nature is completely different: The first one, the usual bulk permeability coefficient, describes the resistance of the skeleton to the flow of the fluid/adsorbate mixture. The second one describes the surface resistance to the outflow of the mixture from the solid. This work shows within a simple example the range of these parameters and the dependence of adsorption/diffusion on them.