Water Content In Porous Media Research Articles

Influence of the water content on the complex conductivity of bentonite

Compacted bentonite is considered as a potential buffer material for deep geological disposals of high-level nuclear wastes. Methodologies to non-intrusively monitor the water content of such sealing materials are important in the context of the safety of these storage facilities and for various engineering applications as well. Induced polarization is a non-intrusive geophysical method sensitive to the water content of porous media. We investigated the complex conductivity spectra of 69 samples made of 2 distinct MX80 bentonites, one in the form of powder from crushed pellets (Type I) and the other in the form of a granulated bentonite mixture (GBM, type II). The samples are prepared at different compaction states and saturations. The pore water conductivity of the porous samples is estimated to be ∼2.5 S m−1 (25 °C) by two different methods. The complex conductivity spectra were obtained at room temperature (25 ± 2 °C) in the frequency range 1 Hz-45 kHz. In-phase and quadrature conductivities reflect conduction (electromigration) and polarization processes, respectively. At a given frequency, both the in-phase and quadrature conductivities increase with the water content along a trend that is independent of the compaction state. An induced polarization model based on the dynamic Stern layer model is used to explain these results. The first Archie's exponent m is inferred from the formation factor F using the in-phase conductivity data versus the pore water conductivity data at different salinities (NaCl, 25 °C). The dynamic Stern layer model applied to polarization correctly predicts the dependence of the in-phase conductivity, quadrature conductivity, and normalized chargeability with the water content and the Cation Exchange Capacity (CEC). This petrophysical work can easily be applied to time-domain induced polarization data collected in field conditions to monitor hydraulic barriers.

Transport and retention patterns of fragmental microplastics in saturated and unsaturated porous media: A real-time pore-scale visualization

The environmental behaviors of microplastics (MPs) have garnered ever-increasing attention globally. To overcome the limitations of commonly used “black box”, a real-time pore-scale visualization system including microscope, charge coupled device (CCD) microscope camera, and flow cell (connected with pump and sample collector) was used to unravel the transport and retention mechanisms of fragmental microplastics (FMPs) in saturated and unsaturated porous media. The breakthrough curves (BTCs) of effluent concentrations from the flow cells were used to quantitatively analyze FMPs transport. The videos gathered from different transport scenarios indicated that FMPs can move along with the bulk flow in porous media, but also move around the sand surfaces via sliding, rolling, and saltating patterns. The FMPs were retained in porous media mainly via deposition and straining in saturated porous media. Interestingly, little FMPs were captured by the air-water interface in unsaturated conditions. The mobility of FMPs varied with environmental factors, which became lower at higher solution ionic strength (IS), smaller grain size, and lower water content in porous media. Flow rate barely affected the transport of FMPs under 0.1 mM IS with the mass recovery rate ranging between 65.8 and 67.5%, but significantly enhanced FMPs mobility under 10 mM IS through reducing the moving rate. The IS and grain size showed a more significant effect on the transport of FMPs in unsaturated porous media. Our findings, for the first time, visually deciphered the transport and retention patterns of MPs with fragmental shapes on pore-scale, expanding our current knowledge of the fate and transport of more realistic MPs in the environment.

Time and frequency domain reflectometry for the measurement of tree stem water content: A review, evaluation, and future perspectives

Electromagnetic (EM) methods for estimation of water content in porous media (e.g., soil and tree stems) are based on estimates of the media's bulk dielectric permittivity, which is sensitive to water content. Time domain reflectometry (TDR) and frequency domain reflectometry (FDR) are routinely used for rapid, automated and minimally destructive approach for routine measurement of soil water content (θsoil) and stem water content (θstem) in the laboratory and field. Applications and advances of TDR and FDR in soil science have been well-documented, but no attempt has been made to critically review the use of EM methods for measuring θstem. In this paper we review the principles, calibration, sensor configuration, and sensor installation of the TDR and FDR methods for the measurement of θstem. Perspectives are presented on new TDR calibration, the development of new sensors, and technologies for the simultaneous measurement of θstem, sap flow, bulk density/porosity, radial distribution of θstem, and electric conductivity. Also discussed were the effects of tree morphology and wounding on the accuracy of both methods. This review provides information for the novice and expert alike to guide them on the advantages, limitations, development, and application of the EM methods required to improve the reliability and validity of measured values of θstem.

Evaluation of consolidation of different porous media with hydraulic lime grout injection

Abstract The grout injection is a technique widely used for structural consolidation of the multi-leafs stone masonry, which often present low compactness and weak links between the internal and external leaves. Grouts can be seen as mixtures of binder with water, with or without special additives. To ensure an adequate flow of the grout and a correct filling of the internal voids inside the masonry, it is essential to assure good fresh grout properties, such as stability, water retention and a rheological behaviour. The grout specification involves the knowledge of the flow capacity within the masonry inner core and physic-chemical compatibility with the original materials present in the historic materials. Thereby, the scope of this paper is to evaluate the injection performance of hydraulic lime based grouts as a function of the porous media to be injected. For this purpose, simplified models were created to allow injectability tests in controlled conditions. To enable the simulation of different permeabilities and internal structures of masonries, the models were created by filling plexiglass cylinders with different grain size distributions of limestone sands and crushed bricks. Since, these materials exhibit different water absorption coefficients, it also was possible to study the influence of water loss from grout to porous media in grout injectability. Another variable studied with influence on grout injectability was the water content of porous media. As it is not expected that masonries are always dried, the pre-wetting of some cylinders by simple injection of water is of extreme relevance to compare the results of grout injectability in the two opposite situations. The grout injection performance was analysed both in the fresh and hardened states. The injectability of the grout as well as its link to the materials within the inner core of old masonries was assessed by tomography and mechanical tests. The mechanical results showed good correlation with injectability and high dependence with the position of the specimen analysed on the cylinder injected, creating tensile strength gradients along the height of the cylinder. Regarding the tomography, the tomographs demonstrate the compactness of the porous media after grout injection. In fact, according to the results obtained, it can be stated that the tomography allows the evaluation of the grout injection capacity to improve the physical and mechanical properties of the inner core of old masonries.

Dielectric relaxation behavior of Callovo‐Oxfordian clay rock: A hydraulic‐mechanical‐electromagnetic coupling approach

Water content is a key parameter to monitor in nuclear waste repositories such as the planed underground repository in Bure, France, in the Callovo‐Oxfordian (COx) clay formation. High‐frequency electromagnetic (HF‐EM) measurement techniques, i.e., time or frequency domain reflectometry, offer useful tools for quantitative estimation of water content in porous media. However, despite the efficiency of HF‐EM methods, the relationship between water content and dielectric material properties needs to be characterized. Moreover, the high amount of swelling clay in the COx clay leads to dielectric relaxation effects which induce strong dispersion coupled with high absorption of EM waves. Against this background, the dielectric relaxation behavior of the clay rock was studied at frequencies from 1 MHz to 10 GHz with network analyzer technique in combination with coaxial transmission line cells. For this purpose, undisturbed and disturbed clay rock samples were conditioned to achieve a water saturation range from 0.16 to nearly saturation. The relaxation behavior was quantified based on a generalized fractional relaxation model under consideration of an apparent direct current conductivity assuming three relaxation processes: a high‐frequency water process and two interface processes which are related to interactions between the aqueous pore solution and mineral particles (adsorbed/hydrated water relaxation, counter ion relaxation and Maxwell‐Wagner effects). The frequency‐dependent HF‐EM properties were further modeled based on a novel hydraulic‐mechanical‐electromagnetic coupling approach developed for soils. The results show the potential of HF‐EM techniques for quantitative monitoring of the hydraulic state in underground repositories in clay formations.

A developed technique for measuring water content in oil-contaminated porous media

Water content is an important physical parameter for soil, vadose zone, and porous aquifer. Accurate measurement of water content in oil-contaminated porous media is critical for the research on oil pollution process and remediation in soil and groundwater systems. In this study, an improved water content calculation formula for oil-contaminated porous media was proposed based on the theory of oven-drying method, and laboratory experiments were conducted to test the applicability and accuracy of the formula for several types of manually prepared oil-contaminated porous media with different water contents. Furthermore, the measuring method and calculation formula, which can be used to determine the water content of porous media sampled from the oil-contaminated sites, were proposed for the first time in this study based on the improved formula. The experimental results showed that the improved formula was very accurate when used to calculate the water contents of diesel-contaminated sand, gasoline-contaminated mild clay, and engine oil-contaminated sand, indicating that it was widely applicable to oils with different volatile ability as well as porous media with different texture. This study meets the urgent need for accurate determination of water content in oil-contaminated porous media, and it solves the technical problem that the existing water content measuring methods cannot be applied directly in the field study.

Transport study in unsaturated porous media by tracer experiment in a dichromatic X-ray experimental device

Estimating contaminant migration in the context of waste disposal and/or environmental remediation of polluted soils requires a complete understanding of the underlying transport processes. In unsaturated porous media, water content is one of the most determining parameters to describe solute migration because it impacts directly on solute pore velocity. However, numerous studies are satisfied with only a global or a partial spatial distribution of water content within the studied porous media. Therefore, distribution of water content in porous media must be precisely achieved to optimize transport processes modeling. Tracer experiments with downward flow were performed on the BEETI experimental device equipped with a sand column. Water content and concentration profiles of tracer (KI) were measured along the column during experiment. The relative dispersion of water content, calculated along the column, gives an idea of influence of this parameter on transport properties. A relationship between pore velocity, Darcy flow velocity and water content is proposed.

DSC(示差走査熱量測定）による多孔質体中の不凍水量に関する研究

DSC(示差走査熱量測定）による多孔質体中の不凍水量に関する研究

Influence of Dispersion on Transport of Tracer through Unsaturated Porous Media

The dispersion phenomenon has resulted from the various water flow magnitude and direction in porous media. The dissolved tracer tends to spread due to dispersion and then travel time of tracer through the porous media increases. In unsaturated porous media, dispersion coefficient varies with non-linear Darcy’s velocity and the water content. These nonlinear dispersions were observed in both of the laboratory scale sand and soil columns (20 cm). The unsaturated infiltration column and tracer tests have been used to interpret the relationships between Darcy’s velocity and the water content together with the dispersion coefficient. However, the dispersivity coefficient cannot be measured directly; it has to be determined from advection-dispersion equation (ADE), which can be used to model the tracer transport in unsaturated porous media. The model was used to describe the non-linear functions of water contents and dispersivities for both porous media. The simulations have been verified that the dispersion of tracer through soil is higher than that of sand column and also the travel time of tracer through soil is longer than that of sand column. Even though, soil has very low degree of pore velocity, high dispersivity is observed in the simulations. The water content and tracer concentration profiles reveal that the increase of dispersivity induces the increase of flow path distance and the decrease of pore velocity. The maximum dispersivity was observed when the water content of porous media is relatively low; this leads to the maximum of spreading of tracer.

Characterization of a spiral‐shaped time domain reflectometry probe

Time domain reflectometry is one of the most common methods to determine water content in porous media. Transmission lines used to carry the electromagnetic pulse can take many different forms and shapes and can be tailored to specific needs. Here we describe the design and characterization of a miniaturized transmission line, specifically designed for applications in laboratory settings. The sensor consists of a spiral‐shaped Cu waveguide, which is constructed by etching techniques used in printed circuit board manufacturing. The waveguides are 0.508 mm wide and have a separation of 0.508 mm. The overall diameter of the spiral is 42 mm, and the overall length of the waveguide is 38 cm. The probe was tested experimentally in media of different dielectric properties using a Tektronix cable tester. The electrostatic field distribution of the probe was simulated using a two‐dimensional numerical solution of the Laplace equation. The numerical analysis was used to compute a weighting function of the measurement and to determine the equivalent dielectric permittivity. For the range of permittivities expected in environmental porous media, such as soils and sediments, the sampling area of the probe was not affected by the water content of the medium.

Continuum percolation theory for pressure–saturation characteristics of fractal soils: extension to non-equilibrium

Systematic experimental deviations from theoretical predictions derived for water retention characteristics of fractal porous media have previously been interpreted in terms of continuum percolation theory (at low moisture contents, below the critical volume fraction of water, α c capillary flow ceases). In other work, continuum percolation theory was applied to find the hydraulic conductivity as a function of saturation for saturations high enough to guarantee percolation of capillary flow. Now these two problems are further linked, using percolation theory to estimate non-equilibrium water retention at matric potential values such that the equilibrium water content is too low for percolation of capillary flow paths. In particular, a procedure for developing a time-dependent moisture content is developed for experimental time scales long enough that film flow can provide an alternate mechanism for equilibrating when continuous capillary flow is not possible. The time scales are defined in terms of moisture-dependent length scales and film flow and capillary flow hydraulic conductivities. Imbibition is treated in the extreme case of no film-flow contribution to equilibration. In another application at higher matric potentials, recursive relations are derived for the water content of porous media during drying when external pressures are changed at rates too rapid for equilibrium to be attained by capillary flow.

Evaluation of distribution coefficients for the prediction of strontium and cesium migration in a natural sand at different water contents

Contaminant distribution coefficient determined under saturated conditions are often used to model solute transport in the vadose zone. However, the water content of porous media may affect the transport behaviour of conservative and sorbing solutes. We performed column experiments using sand from Chernobyl area and we investigated the transport of tritiated water as conservative tracer, 85 Sr and 134 Cs as reactive solutes at different water saturation levels. The results indicate that when the Kd model is applicable, a decrease of the water content leads to a decrease of the Kd value.

Evaluation of a method to measure water content in porous media by employing ultrasound

A method to measure water content in porous media, such as soils and grains, was developed as a real time nondestructive test. The method was based on piezoelectric ultrasonic transducers as a sensor system. Transmitters and receivers was developed to administrate the sensors system and ultrasonic signal. Transmitters and receivers are placed facing each other and located inside the porous media 10 cm apart. The method was evaluated in two porous media, namely a column 30 cm coarse sand and a paddy rice variety Fedearroz 50, in order to evaluate the sensors system performance in two different porous media with different water holder capacity. Tools were developed for data acquisition, capacity of 16 analog signal, 12 bits resolution. Electronic circuits, C++ OOP programming and Matlab were used. The results showed a monotonically increment of millivolts as a response of the transducer as the water content was decreasing.

TDR measurements of hydraulic jump aeration in the South Fork of the American River, California

Turbulent pressure and velocity fluctuations associated with hydraulic jump air entrainment likely play an important role in local flow dynamics and morphologic changes of steep bedrock and alluvial rivers. Previous engineering research indicates that hydraulic jump air entrainment and energy dissipation locally intensify erosion of both bedrock and alluvial elements, enhance hydraulic quarrying, suppress cavitation, and decrease the friction factor of a flow. Despite studies in artificial settings, air content in natural hydraulic jumps remains largely unquantified. In this study, Time Domain Reflectometry (TDR), a method commonly used to determine the volumetric water content of porous media for the last two decades, was evaluated in the laboratory and then adapted to measure air contents of natural hydraulic jumps. Laboratory tests were conducted to determine the influence of turbulence, temperature, and sampling volume on the TDR signal over an air content range of 0–100%. Based on the results of the laboratory tests, an empirical calibration was developed that converts the TDR signal into air content. Local air contents were then measured in hydraulic jumps occurring along a mixed alluvial- and bedrock-dominated 8.4-km section of the South Fork American River. Two small jumps had a mean air content of 19% and 23%, a coefficient of variation (CV) of 27% and 28%, and a root-mean-square (RMS) of 19% and 24%, respectively. A large jump had a mean air content of 42%, a CV of 26%, and a RMS of 44%. TDR provides fast, accurate, repeatable, and nondestructive in situ measurements at one-tenth the cost of traditional methods and is far more robust for field applications than traditional lab instruments. Future studies can now expand upon the hydrogeomorphic and ecological significance of jump aeration.

Influence of water content in river sand on the self-brightening of acoustic waves

Results of laboratory experiments on the propagation of high-frequency acoustic waves ( f=100 kHz) in a glass tube filled with river sand are presented. Several sand samples have been used with different water content: dry, partially and completely water saturated. It is shown that the dissipative coefficient of acoustic waves decreases with increasing wave amplitude. This ‘self-brightening’ phenomenon takes place over the whole range of moisture content, from 0 to 100%, but its degree of manifestation depends on the moisture content. The exponent of the dissipative non-linearity α, is found to be the most sensitive parameter to the moisture content and is determined on the basis of measurements. It is considered to be a good indicator of water content in porous media and provides an opportunity to measure water content in such materials indirectly by means of an acoustic method. A simple phenomenological model is presented to explain the experimental results.

Effect of water content on solute transport in a porous medium containing reactive micro-aggregates

The water content of porous media may substantially affect the transport behaviour of conservative and sorbing solutes. Physical processes potentially involved include alterations of the flow velocities, flow patterns, or of accessible surface sites. We performed column experiments using a synthetic porous medium, in which a substantial part of the sorption sites was concentrated in regions within small grained aggregates that were accessible only by diffusion, a feature often found in natural soils and sediments. We investigated the transport of solutes exhibiting very different sorption characteristics under steady state conditions at different water contents of the porous medium. The tracers used were either nonreactive, partitioned into organic matter or sorbed specifically and nonlinearly to clay minerals. Hydrodynamic dispersion generally increased with decreasing water content, reflected by the breakthrough curves (BTCs) of conservative and only slightly sorbing tracers, which exhibited stronger spreading and early breakthrough of the fronts at lower water saturation. Nonlinear sorption and nonequilibrium mass transfer between the mobile region and the immobile water present within the aggregates dominated the BTCs of the strongly sorbing tracer at all degrees of water saturation, and, thus, rendered the effects of increased hydrodynamic dispersion negligible. Due to a relative increase in the ratio of sorption sites per water volume, the retardation of this tracer distinctly increased at low water contents of the porous medium. Solute transport of all tracers was successfully simulated with an advective–dispersive transport model that considered the respective sorption behaviour and retarded intra-aggregate diffusion as predominant processes. All parameter values of the model had been determined previously in independent experiments under completely saturated conditions. Our results demonstrate that a well parameterised transport model that was calibrated under completely saturated conditions was able to describe rate-limited advective-dispersive transport of reactive solutes also under unsaturated steady-state conditions. Enhanced relative retardation of strongly sorbing compounds under such conditions is likely to affect biological and chemical transformation processes of these compounds.

Comparison of empirical and partly deterministic methods of time domain reflectometry calibration, based on a study of two tropical soils

The use of time domain reflectometry for the determination of volcanic soils' moisture content in tropical areas has shown the necessity to set up an accurate calibration. We chose to test the most representative calibration models on two tropical volcanic soils coming from two different climatic areas of the Réunion Island. The empirical model of Topp et al. [Topp, G.C., Davis, J.L., Annan, A.P., 1980. Electromagnetic determination of soil water content: measurements in coaxial transmission lines. Water Resources Research, 16 (3) 574–582.] was found to offer the best accuracy/simplicity trade-off for simulations with a cambisol, with an accuracy of ±2.46 dielectric constant points (or about ±2.7% for a water content close to 45%). In contrast, it gave poorer results for analysis of the andosol containing the greatest quantity of amorphous minerals (±5.74 dielectric constant points). The partly deterministic models were found to be better for this latter application, including that of Ansoult et al. [Ansoult, M., De Backer, L.W., Declercq, M., 1985. Statistical relationship between apparent dielectric constant and water content in porous media. Soil Sci. Soc. Am. J., 49, 47–50.] which gave the best accuracy (±3.84 dielectric constant points). For both soil materials studied, there was only a slight gain of accuracy by introducing a specific polynomial calibration determined in the laboratory: ±1.72 and ±3.46 dielectric points for the cambisol and the andosol, respectively. Choices of models to be used should thus be based on the type of soil to be analysed and accuracy requirements.

Test of a Heat‐Pulse Probe for Measuring Changes in Soil Water Content

AbstractThe maximum temperature rise measured at some distance from a line heat source can be used to determine the volumetric heat capacity and hence water content of porous media. We describe a simple heat‐pulse device for determining the volumetric heat capacity and hence water content of porous media. The device consists of three needle probes (0.813‐mm diam., 28 mm long) mounted in parallel. The heater probe contains a heating element while the sensor (mounted 6 mm from the heater) and reference probe (mounted 20 mm from the heater) contain thermocouples. The reference probe can be used to automatically correct for changes in background temperature. Measurements made at three depths during drying of a laboratory soil column yielded accurate changes in soil water content provided actual heater‐to‐sensor probe spacings were used in the calculations. We describe a simple procedure for checking on the probe spacings once the probes have been installed. These heat‐pulse devices should prove useful for monitoring wetting or drying changes in soil water under both laboratory and field conditions.

Statistical Relationship between Apparent Dielectric Constant and Water Content in Porous Media

AbstractA theoretical relationship between the apparent dielectric constant (Ka) and the water content (θr) of porous media is presented. The dielectric effect of the porous medium is investigated at the microscopic scale of the probable path of an electric charge. This path is a function of the environment of the charge. Only one parameter, the number of degrees of freedom of the charge is necessary to describe the heterogeneity of the porous medium. The results of this model generally agree very well with recently published experimental data.