Showing papers on "Permeability (earth sciences) published in 1992"

The RETC code for quantifying the hydraulic functions of unsaturated soils

Abstract: This report describes the RETC computer code for analyzing the soil water retention and hydraulic conductivity functions of unsaturated soils. These hydraulic properties are key parameters in any quantitative description of water flow into and through the unsaturated zone of soils. The program uses the parametric models of Brooks-Corey and van Genuchten to represent the soil water retention curve, and the theoretical pore-size distribution models of Mualem and Burdine to predict the unsaturated hydraulic conductivity function from observed soil water retention data. The report gives a detailed discussion of the different analytical expressions used for quantifying the soil water retention and hydraulic conductivity functions. A brief review is also given of the nonlinear least-squares parameter optimization method used for estimating the unknown coefficients in the hydraulic models. Several examples are presented to illustrate a variety of program options. The program may be used to predict the hydraulic conductivity from observed soil water retention data assuming that one observed conductivity value (not necessarily at saturation) is available. The program also permits one to fit analytical functions simultaneously to observed water retention and hydraulic conductivity data. The report serves as both a user manual and reference document. Detailed information is given on the computer program along with instructions for data input preparation and sample input and output files. A listing of the source code is also provided.

On Flow through Aligned Fiber Beds and Its Application to Composites Processing

Abstract: In process modeling of continuous fiber composites, matrix flow through aligned fiber beds is traditionally described by Darcy's law, which relates matrix flow rate to matrix pressure gradient, matrix viscosity, and fiber bed permeability. This phenome nological relationship was originally derived for macroscopically isotropic beds of spheri cal or sphere-like particles. Hence it is necessary to establish the conditions under which this relationship may be extended to fiber beds, which are approximately transversely iso tropic. A review of previous work on steady-state Newtonian fluid flow through isotropic porous media is used as a foundation to explore the validity of extending Darcy's law to flow through beds of aligned fibers. Theoretical analyses are compared to experimental results obtained from flow through real fiber beds and ideal beds of regularly spaced cylinders. Functional relationships for flow of generalized Newtonian fluids through iso tropic sphere beds are also reviewed, and their extens...

Determination of the Effective-Stress Law for Permeability and Deformation in Low-Permeability Rocks

Abstract: This paper reports that laboratory experiments were performed to determine the effective stress law of tight sandstones and chalk for permeability and deformation. Permeability and volumetric strain data were taken at various stresses and pore pressures and were analyzed with a statistical model-building approach. Results show that the effective stress laws for both processes are variable with stress and pressure, depend on the material, and do not agree well with present theories. This may be applied for a greater understanding of oil reservoir formations.

The effects of fluid escape on accretionary wedges 2. Seepage force, slope failure, headless submarine canyons, and vents

Abstract: The high pore pressure gradients inherent to accretionary complexes affect the force balance of the wedge via seepage force, which acts in the direction of flow and is proportional to the pressure (head) gradient. If sufficiently large, this seepage force can offset gravity and friction and lead to failure. At the toe of the wedge sediments are weak, slopes are over-steepened by folding and faulting, and fluid pressure gradients can be high; these conditions are conducive to seepage-induced failure. For the 14–16° slope at the toe of the southern Cascadia wedge, the pore pressure gradient necessary to initiate failure is λ=0.74–0.86. The gradient necessary to cause failure is sensitive to surface slope and sediment strength, but is insensitive to porosity. Reasonable estimates of sediment strength for most accretionary wedges require pore pressure gradients ranging from 10 to 60% of lithostatic to cause failure. These values are within the range of modeled and measured pore pressures in accretionary complexes, suggesting that seepage-induced slope failure should be an expected feature in this environment. If these failure features are observed, then their presence can be used to constrain the pore pressure gradient within the wedge, independent of any assumptions regarding fluid discharge or permeability. If seepage failure repeats and is localized in the same region, then it can lead to channel, gully, and canyon formation. Two convergent margins, southern Cascadia and northern Hispaniola, show many regularly spaced headless canyons that cannot be attributed to downslope erosive flow. We suggest that these canyons are forming from internally driven seepage-induced failure. Both the Oregon and Hispaniola accretionary wedges also contain evidence for non-uniform fluid flow based on the observed and inferred presence of vents. Using Darcy's Law, the pore pressure constraint from the slope failure analysis and an estimate of the total fluid discharge, we examine the relationship between wedge and vent permeabilities, the areal extent of focused fluid venting, and the percent of the total fluid discharge that flows out of vents. Given reasonable estimates of the total fluid discharge out of the southern Cascadia wedge, we find that the wedge must be less permeable than 2 × 10−17 m2 in order for focused fluid venting to occur at all. If the permeability of the vents is much higher than the wedge permeability, then the vents will occur over a very small percentage of the wedge; these vents, however, could accommodate much of the fluid flowing out of the wedge. Using permeability measurements from samples collected at the toe of the Oregon margin [Horath, 1989], we estimate that vents at the toe of the southern Cascadia accretionary complex comprise less than 0.2% of the wedge area, but that these vents can accommodate up to 60% of the total fluid discharge.

Effects of freezing on hydraulic conductivity of compacted clay

Abstract: A compacted clay is subjected to five cycles of freezing and thawing at constant water content. The test specimens are then permeated in flexiblewall permeameters at a relatively low effective stre...

Chapter 9 Measurement of Permeability and Storage Capacity in Rocks During Deformation at High Temperature and Pressure

Abstract: Both permeability and storage capacity have been determined in a marble, a limestone, and a sandstone during deformation at high pressure and temperature. The method used utilizes the attenuation and phase retardation of a sinusoidal pore pressure oscillation as it propagates through a sample under test. These parameters were measured at a confining pressure of 300 MPa, argon pore fluid pressures ranging from 20 to 270 MPa, temperatures to 873 K and strains of 0, 10% and 20%. The results for marble indicate that temperature elevated to moderate levels can enhance both the permeability and storage capacity owing to the anisotropy in thermal expansion of the constituent minerals, while the activation of plastic processes at higher temperatures causes the collapse of void spaces and reduction of permeability and storage capacity. It has been observed at all temperatures, however, that when the pore fluid pressure approaches the confining pressure, both measured parameters increase rapidly, and also that ongoing deformation can, when pore pressure remains relatively high, have a profound effect on the transport and storage properties of polycrystalline materials, pushing the measured permeability to up to two orders of magnitude above the level of virgin rock. A model analysis is presented from which information regarding the in-situ pore structure under the experimental conditions can be deduced (permeability, storage capacity, pore structure, crack aspect ratio).

Permeability of thermally cracked granite

Abstract: Permeability of granite specimens heated up to 650°C were measured in the laboratory with respect to both confining and pore pressure. An unexpected behavior (permeability decrease) was found in the low temperature range (20–125°C). Permeability variations are interpreted with the help of a theoretical model of porosity. Complementary measurements of porosity and absolute surface area have also been obtained. A discussion in terms of microstructural controlling parameters concludes to a decrease of crack aperture at low temperatures (20–125°C), followed by an increase at higher temperatures (T >125°C).

Impact of fracture coatings on fracture/matrix flow interactions in unsaturated, porous media

Abstract: Groundwater flow in unsaturated, fractured rock is often assumed to be dominated by the porous matrix component. This is frequently the result of reasoning that water flowing in the fractures is rapidly imbibed into the rock matrix by capillary suction forces with negligible resistance to uptake at the fracture/matrix interface. However, the existence of a low-permeability mineralized layer or coating at this interface may substantially reduce matrix imbibition and could consequently result in fracture-dominated flow. To test this idea, four tuff samples containing natural fractures were obtained from tuff formations in southern Nevada. By performing imbibition experiments into the matrix rock, across a mineralized fracture face and then across a fresh uncoated fracture face, water uptake as a function of time and coating was measured. A model combining Darcy's law and the Washburn equation has been used to describe the imbibition behavior. Before testing the tuff samples, the experimental technique and imbibition model were first tested using ordered sphere packings with known pore size and structure. From the tuff imbibition data, the ratio of the permeability through the mineralized face to the permeability through the uncoated face was found to be 0.3 (relatively little effect of the mineralized layer) for two samples, 0.01 for one sample, and 10−7 (uptake strongly restricted by the mineralized layer) for one sample. Using a simple fracture flow model and the imbibition model mentioned above to simulate matrix uptake from the fracture, numerical simulations indicate that the existence of fracture coatings could significantly decrease the travel time and increase the travel depth of water flowing through fractures.

Estimating the mean permeability: how many measurements do you need?

Abstract: The question of the number of permeability measurements that are required to estimate the mean permeability of a reservoir interval is not generally considered during reservoir evaluation. Permeability sampling is traditionally carried out with core plugs (1.0-1.5 inch or 2.5-3.8 cm cylindrical samples) at a spacing of about 1 foot or 0.3 m. This spacing has evolved from considerations of practicality, cost and the need for core conservation, and takes little account of the underlying rock variability.

Physical properties of ash flow tuff from Yucca Mountain, Nevada

Abstract: We have measured the density and determined the porosity of 198 samples of ash flow tuffs from three boreholes at Yucca Mountain, Nevada. The electrical properties, velocity, and permeability of many of these samples have also been determined. We use mineralogical and physical data from other sources to determine the dependence of measured physical properties upon petrology. Porosity in the samples varies over a wide range, from as low as 1% in the densely welded tuffs to 53% in the zeolitized nonwelded tuffs. Porosity is the primary control on the other measured physical properties that consequently vary over broad ranges. Alteration (zeolites and clays) is a primary control on grain density and a significant secondary control on bulk density, resistivity, velocity, and permeability. Sorting the samples into rock classes defined in terms of the degree of welding and gross mineralogy enables us to separate the influence of zeolites and clays from that of porosity. Empirical rock property relationships established for sandstones can be applied with good success to tuffs. Archie's law relating resistivity to porosity is found to fit the unaltered samples with an exponent m of 2.0. An empirical expression relating compressional velocity to porosity and clay content forms an excellent upper bound to the velocity-porosity data. Permeability-porosity plots are similar in form to those obtained for clastic rocks, although the permeability is considerably lower than in clastic rocks of similar porosity. Zeolites and clays reduce the grain density, increase the electrical conductivity, reduce the compressional velocity, and reduce the permeability.

Forward modelling of porosity and pore pressure evolution in sedimentary basins

Abstract: The gravitational compaction of sediments is an important process in forward basin modelling. This paper presents a mathematical model for the one-dimensional compaction of an accreting layer of argillaceous sediments. Realistic constitutive laws for the clay compressibility and the clay permeability, based on soil mechanics tests, were incorporated into the model. The governing equations were put in dimensionless form and the extent of abnormal pore fluid pressure development was found to depend on the sedimentation parameter, a dimensionless group representing the ratio of the sediment hydraulic conductivity to the sediment accumulation rate. The effects of clay compressibility were studied and highly colloidal clays such as montmorillonite developed higher overpressures than less compressible materials. The results also showed that overpressuring developed in shales for cases in which the clay permeability did not go to zero in the limit of zero porosity. Linear models based on simplifying assumptions inappropriate for sedimentary basins were found to give significantly different estimates for the conditions leading to overpressuring. Using reasonable ,parameters, the model adequately reproduced porosity and pore pressure profiles measured in the sandshale sequences of the South Caspian Sea.

Pore-Size-Dependent Apparent Viscosity for Organic Solutes in Saturated Porous Media

Abstract: The value of hydraulic conductivity under saturated conditions, K, depends on the nature of the porous medium and the physical properties of the perfusing fluid. The equation K = kρg/η, where k is the permeability, η is the fluid viscosity, ρ is the fluid density, and g is the gravitational constant, has been used to account for porous medium and fluid properties on K. A laboratory study was conducted to determine whether the equation properly accounts for viscosity effects of organic solutes on K. Hydraulic conductivity of 0, 25, 50, 100, 200, 300, and 400 mg L⁻¹ solutions of large molecular weight polyacrylamides (PAM); 0, 10, 20, 30, 40 and 50% (v/v) of glycerol in distilled water; and undiluted n-propanol was measured in two size fractions of quartz sand. The apparent viscosities of PAM and glycerol solutions were higher in the fine sand than in the coarse sand. The apparent viscosity of n-propanol was about the same in the two sand-size fractions. The above-stated equation did not properly account for the effects of fluid properties of PAM and glycerol on K. Use of viscosity values as measured by a viscometer in the equation could result in a several-fold error in prediction of K. Quantitatively characterizing those conditions under which the equation is valid may be important in analyzing the transport of environmental contaminants through soil, particularly when the contaminants may be organic chemicals of various molecular sizes and conformations. This research was supported by the Univ. of California Kearney Foundation of Soil Science.

Hydraulic conductivity of a recent estuarine silty clay at Bothkennar

Abstract: In characterizing the estuarine clay at Bothkennar, Scotland, the hydraulic conductivity (permeability) was studied. In situ the hydraulic conductivity was determined using pushed-in-place piezometers, self-boring permeameters and the BAT system; in the laboratory oedometer cells, triaxial cells and a radial flow cell were used to determine the vertical and horizontal hydraulic conductivities and their variation with vertical compression. The results show a size effect and an anisotropy ratio varying with the fabric of the soil, but typically between 1·5 and 2. They also indicate that the pushed-in-place piezometers and the BAT system underestimate the hydraulic conductivity. The most representative profile seems to be given by the self-boring permeameter. The variation with compression of the hydraulic conductivity can be characterized by Ck=0·5 e0. Pour caracteriser l'argile d'estuaire a Bothkennar, Ecosse, la conductivite hydraulique (permeabilite) a ete etudiee. In situ la conductivite hydraulique a e...

Permeability Transects of Eolian Sands and Their Use in Generating Random Permeability Fields

Abstract: This paper reports on observations derived from more than 10,000 permeability measurements taken from eolian sands and their use in generating permeability fields for reservoir simulation input. Results show that classification and statistical measures of variability and spatial correlation (but not mean permeability) are portable between the outcrop and the subsurface.

Fluid flow in compressible porous media: I: Steady‐state conditions

Abstract: This is the first of two articles dealing with fluid flow in compressible porous media. In this article a model describing fluid flow and pressure-induced variations in porosity under stationary conditions is developed. In a forthcoming article the dynamic behavior during filtration and wet pressing of compressible porous media are presented. Fluid flow through rigid porous media is generally described by Darcy's law. The corresponding expression for compressible materials is derived in this article. This expression, the steady-state flow (SSF) equation, allows the steady-state flow to be easily calculated, either numerically, or by using the approximative analytical solutions that are also presented here. In the SSF equation optional empirical and/or theoretical permeability and compressibility relationships may be combined. Further, a new compressibility model which also applies for viscoelastic materials is presented. The influence of the compressibility of the material and the influence of precompression is illustrated. (Less)

Characterization of non-Darcy multiphase flow in petroleum bearing formations. Annual status report, May 14, 1991--May 13, 1992

Abstract: The objectives of this research are: Develop a proper theoretical model for characterizing non-Darcy multi-phase flow in petroleum bearing formations. Develop an experimental technique for measuring non-Darcy flow coefficients under multiphase flow at insitu reservoir conditions. Develop dimensional consistent correlations to express the non-Darcy flow coefficient as a function of rock and fluid properties for consolidated and unconsolidated porous media. The research accomplished during the period May 1991--May 1992 focused upon theoretical and experimental studies of multiphase non-Darcy flow in porous media.

Well-conditioned iterative schemes for mixed finite-element models of porous-media flows

Abstract: Mixed finite-element methods are attractive for modeling flows in porous media since they can yield pressures and velocities having comparable accuracy. In solving the resulting discrete equations, however, poor matrix conditioning can arise both from spatial heterogeneity in the medium and from the fine grids needed to resolve that heterogeneity. This paper presents two iterative schemes that overcome these sources of poor conditioning. The first scheme overcomes poor conditioning resulting from the use of fine grids. The idea behind the scheme is to use spectral information about the matrix associated with the discrete version of Darcy’s law to precondition the velocity equations, employing a multigrid method to solve mass-balance equations for pressure or head. This scheme still exhibits slow convergence when the permeability or hydraulic conductivity is highly variable in space. The second scheme, based on the first, uses mass lumping to precondition the Darcy equations, thus requiring more work per i...

Estimation of radial permeability distribution from well-test data

Abstract: This paper presents a method of estimating a radial permeability distribution that would reproduce the pressure data obtained in a well test. The method is applied to three examples: permeability variation in a composite reservoir, porosity variation in a composite reservoir, and permeability variation with inaccurate data. The permeability estimates obtained are shown to be smoothed versions of the actual permeability distribution, and an estimate for the resolution width of the smoothing is provided. One significant advantage of the solution method applied in this paper is the ability to estimate permeability variation without dividing the reservoir into zones of constant permeability

The Resistance to Flow Transmission of Porous Materials

Abstract: This paper presents a model to predict the permeability of woven fabrics. A capillary model of porous systems based on Poiseuille's formula (laminar flow) and D'Arcy's Law (laminar and turbulent flow) is used. The determination of permeability is based on the corrections proposed in previous papers.

Carbonate reservoir characterization : a geologic-engineering analysis, part 1

Abstract: 1. Introduction (G.V. Chilingarian, S.J. Mazzullo, H.H. Rieke). Important, relatively new concepts. Traditional concepts: classification schemes. Reserve analysis of carbonate reservoirs. Reserve calculation methods. Fractured reservoir rocks and fractures. Relative permeability concepts. Prediction of overpressured formations in carbonate reservoirs. Appendices: Material balance equation. Application of petrography and statistics to the study of some petrophysical properties of carbonate reservoir rocks. 2. Carbonate Rock Classifications (S.J. Mazzullo, G.V. Chilingarian, H.J. Bissell). Classification of limestones. Classification of dolomites. Classification of dolomites of marine origin. 3. Depositional Models of Carbonate Reservoirs (S.J. Mazzullo, G.V. Chilingarian). Stratigraphic traps in carbonate rocks: a review. Depositional facies in marine carbonate rock reservoirs. Platform types. 4. Diagenesis and Origin of Porosity (S.J.Mazzullo, G.V. Chilingarian). Overview of concepts. Methods of diagenetic study. Porosity characteristics of carbonate sediments and rocks. Formation of secondary matrix porosity in limestones. Porosity in dolomites. Reservoir examples. 5. Carbonates as Hydrocarbon Source Rocks (R.J. Cordell). Characteristic lithologies of carbonate source beds. Depositional environments. Environmental interpretations from geochemistry. Diagenesis. Source-bed geochemistry. Maturation.Effects of clay minerals. Maturation examples. Migration mechanisms. Matching source with reservoir. 6. Pore Geometry of Carbonate Rocks and Capillary Pressure Curves ( Basic Geologic Concepts ) (R.L. Jodry). Classification of carbonate porosity. Capillary pressure curve interpretation. Interrelation between pore geometry and rock types. Application of pore geometry characteristics to exploration. Pore geometry of dolomites. 7. Interrelationships among Surface Area, Permeability, Porosity, Pore Size, and Residual Water Saturation (G.V. Chilingarian, J. Torabzadeh, H.H. Rieke, M. Metghalchi, S.J. Mazzullo). Theoretical and empirical equations relating porosity, permeability, and surface area. Statistical technique of determining specific surface area. Interrelationships among surface area, rock granulometric composition, porosity, permeability, and residual water saturation. 8. Permeability and Relative Permeability of Carbonate Reservoirs (M.M. Honarpour, G.V. Chilingarian, S.J. Mazzullo). Relationship between effective and absolute permeability. Permeability parallel to bedding versus permeability perpendicular to bedding. Effects of rock properties on relative permeability. Effects of saturation history on relative permeability. Effects of temperature on relative permeability. Laboratory- measured relative permeability examples. Three-phase relative permeability of carbonate rocks. Empirical correlation. 9.Compressibility (G.V. Chilingarian, J. Torabzadeh, J.O. Robertson, H.H. Rieke, S.J. Mazzullo).

Impact of Permeability and Lithology on Gel Performance

Abstract: This paper describes an experimental investigation of the effects of rock permeability and lithology on the performance of several gels, including those formed from resorcinolformaldehyde, colloidal silica, chloride)-xanthan, and acetate)-polyacrylamide. During these experiments, particular attention was paid to (1) the importance of pH to gelation, (2) gel performance as a function of fluid velocity, and (3) the use of tracers to assess the fraction of the pore space that was occupied by gel. During core experiments, the "strongest" gels were found to reduce the permeability of all cores to approximately the same value (in the low microdarcy range). Tracer studies indicated that these gels occupied most of the available pore space. Flow experiments were performed in rectangular micromodels to determine whether these gels have some inherent permeability to water. The permeabilities for five gels were found to be less than or equal to 60 pD. For "weaker" gels (i.e., those leaving a significant permeability), residual resistance factors generally decreased with increased rock permeability. Tracer studies indicated that these gels occupied a small fraction of the pore space in a core. Experiments revealed that gelation in the porous rock was often far less complete than that in a bottle. For unbuffered gelants in porous rocks, the pH at which gelation occurs may be determined more by rock mineralogy than by the pH of the injected gelant. Thus, the buffering action of reservoir rocks should be considered when evaluating gel performance in the laboratory. The immense buffering capacity of limestone can effectively preclude the propagation of unbuffered chloride)-xanthan gelants or CrC13 solutions through porous limestone. Introduction Ideally, gel treatments should reduce channeling of fluids through high-permeability, watered-out flow paths without damaging oil-productive zones. However, in most applications, the gelant penetrates to some extent into lowpermeability, oil-productive zones. A gel treatment can either enhance or harm oil production, depending on how the gel's performance in low-permeability rock compares with that in the "thief' zone.'^^ Some researchers have attempted to evaluate the effectiveness of fluid diversion processes using porous media with only one ~ e r m e a b i l i t ~ . ~ ~ Unfortunately, this type of evaluation indicates nothing about the performance of the diversion process in strata with different permeabilities. For example, assume that a diverting agent reduces the flow capacity of a "thief' zone by a factor of ten. If the diverting agent reduces the flow capacity of a nearby oil-productive zone by a factor of two, then the fluid diversion process could impro~e sweep efficiency. However, if the diverting agent reduces the flow capacity of the oil-productive zone by a factor of twenty, then the diversion process could reduce sweep efficiency substantially. Thus, the effectiveness of a diversion process cannot be assessed by using rock with a single permeability. Other researchers have used parallel linear corefloods with cores of different permeabilities to evaluate the effectiveness of fluid diversion pro~esses.~'~ Unfortunately, these studies can be extremely misleading for several rea~ons.'"'~ First, the results are not relevant to unfractured wells where the flow geometry is radial. Simple calculations using the Darcy equation reveal that the performance of a diverting agent can be substantially different in a radial geometry than in a linear ge~metry.'.'~ Second, the short bank of the diverting agent in the less-permeable core can be diluted enough by diffusion and References and figures at end of paper. 1

Low permeability subterranean formation testing methods and apparatus

Abstract: The present invention provides methods and apparatus for determining the gas permeability of very low permeability subterranean formations as well as the gas permeability reducing effects of injecting one or more treatment fluids thereinto. A gas is injected into a core sample of the formation at a selected substantially constant pressure, and the injection is continued for a long period of time to insure steady state flow conditions. The temperature of the gas as it flows through the core sample and the flow rate of the gas exiting the core sample are measured, and the native state gas permeability of the core sample is calculated therefrom. One or more treatment fluids can be injected into the core sample after the native state permeability is determined. Thereafter, the gas permeability can again be determined and compared to the native state permeability.

Cement kiln dust management: permeability

Abstract: Three samples of cement kiln dust were selected to represent three groups of kiln systems: long wet, long dry, and precalciner kiln. Chemical composition and physical characteristics of the dusts were studied. The principal objectives of the experimental study was the determination of their permeability to water. Taking a standard geotechnical engineering approach, it was decided to treat these materials as soils capable of compaction, and to determine their permeability as a function of density. Although the dusts covered a very large range of particle size, free lime content, etc., it was found that they were indeed amenable to normal compactive effort, giving familiar moisture-density curves that provided target maximum dry densities, and corresponding optimum moisture contents. The densities so obtained are maxima only for the standard effort; thus higher densities are achievable as the compactive effort is increased. Specimens of each dust were prepared at three levels of density: low, standard laboratory maximum, and high. Permeabilities were determined by means of a constant head permeameter designed to permit measurements over a very wide range of permeabilities. The results indicated consistent inverse relationship between permeability and density for each dust, and that extremely low permeability could be achieved in each case.

Critical gradients and pressures in dense swelling clays

Abstract: Uncertainties exist with regard to the applicability of Darcy's law to dense swelling clays. These clays may not allow water to pass through them when the hydraulic gradient is below a critical value. Preliminary results are presented from a series of constant-head permeability tests on dry, confined, densely compacted bentonite clays. The tests are intended to clarify the applicability of Darcy's law to dense bentonites: these materials may be used for isolation of nuclear fuel wastes in deep geologic disposal vaults. On wetting and with increasing hydraulic gradient, the clays develop swelling pressures, and some specimens appear to exhibit a critical hydraulic gradient or pressure. Below these gradients and pressures, water does not appear to flow through the materials. Once the apparent critical gradient is exceeded, water flux through the materials increases linearly and directly with gradient. Water continues to flow if the gradient is subsequently decreased to values below the original critical val...

On wave propagation in saturated and partially saturated porous media

Abstract: Samenvatting