Saturated Permeabilities Research Articles

Fragility assessment for the rainfall-induced embankments on silty soils

The fragility curve expresses the probability that an asset exceeds some serviceability state for a given level of environmental perturbation or other loadings. It is an important component in the quantitative risk analysis and resilience evaluation of infrastructure exposed to natural hazards. Incidences of over-settlement of embankments are increasingly reported due to more intense and longer-duration rainfall events. This paper develops fragility curves for the rainfall-induced embankment settlement. For this purpose, an embankment incorporating enhanced seepage and displacement analysis within unsaturated soil conditions is modelled based on a reported case history. A Monte Carlo simulation is used for rainfall infiltration and embankment deformation analysis under various rainfall scenarios. Probability values are obtained to achieve three levels of damage states in terms of road embankment settlement. The parametric analysis produces the exceedance probability curves for various rainfall intensities, saturated permeabilities and embankment slope angles. This work offers an efficient tool for assessing fragility to rainfall-induced excessive settlement of embankments.

In-plane permeability changes of plain weave glass fabric induced by tufting

The presence of the tufts has direct influence on the permeability of textile preforms. In this paper, new insights are presented into the mechanisms responsible for changes to the in-plane permeability of tufted preforms according to three different tufting patterns relative to flow direction with a constant tufting distance. The saturated permeabilities are measured based on the rectilinear flow in a tool constituted by a steel base, a transparent PMMA top, and steel supports. Beforehand, the permeability measurements of textile preform composed of eight layers of plain weave glass fabric without tufting are conducted at three different cavity heights. The results show that the in-plane permeability values for the tufted preforms are lower than the permeability values of the preform without tufting. The paper reveals the significant influence of the tufting patterns on the permeability values for three different fibre volume fractions.

An experimental and analytical study based on fractal theory of satin fabrics in unsaturated permeability

Prediction of relative permeability is important to avoid dry spots or micro voids in the liquid composite molding process. Most of previous studies focused on plain and twill, but few are about stain and none of them provide explicit equation to calculate accurate values of unsaturated permeability. The main purpose of this work is to first propose a new model which is proposed mainly based on fractal theory and has no empirical constant in the expression, to calculate the permeability of satin fabric. And then we employ a new experimental method to calculate the unsaturated permeability. Finally, a contrast experiment of 5-harness fabric and 8-harness fabric is designed at different injection pressures, and the accurate values of permeability are obtained. The results show that unsaturated and saturated permeabilities are in the same order of magnitude; furthermore, unsaturated permeability is 77% of saturated permeability in 5-harness fabric and 73% in 8-harness fabric.

Flow modelling of quasi-Newtonian fluids in two-scale fibrous fabrics

Permeability is the fundamental macroscopic material property needed to quantify the flow in a fibrous medium viewed as a porous medium. Composite processing models require the permeability as input data to predict flow patterns and pressure fields. In a previous work, the expressions of macroscopic permeability were derived in a double-scale porosity medium for both Newtonian and generalized Newtonian (shear-thinning) resins. In the linear case, only a microscopic calculation on a representative volume is required, implying as many microscopic calculations as there are representative microscopic volumes in the whole fibrous structure. In the non-linear case, and even when the porous microstructure can be described by a unique representative volume, a large number of microscopic calculations must be carried out as the microscale resin viscosity depends on the macroscopic velocity, which in turn depends on the permeability that results from a microscopic calculation. An original and efficient offline-online procedure was proposed for the solution of non-linear flow problems related to generalized Newtonian fluids in porous media. In this paper, this procedure is generalized to quasi-Newtonian fluids in order to evaluate the effect of extensional viscosity on the resulting upscaled permeability. This work constitutes a natural step forward in the definition of equivalent saturated permeabilities for linear and non-linear fluids.

Unsaturated and Saturated Permeabilities of Fiber Reinforcement: Critics and Suggestions

In general, permeability measurement results show a strong scattering according to the measurement method, the type of test fluid and the fluid injection condition, even though permeability is regarded as a unique property of porous medium. In particular, the discrepancy between the unsaturated and saturated permeabilities for the same fabric has been widely reported. In the literature, relative permeability has been adopted to model the unsaturated flow. This approach has some limits in the modeling of double-scale porosity medium. We address this issue of permeability measurement by rigorously examining the mass conservation condition. Finally, we identify that the pressure gradient is non-linear with positive curvature in the unsaturated flow and a misinterpretation of pressure gradient is the main reason for the difference between the saturated and unsaturated permeabilities of the same fiber reinforcement. We propose to use a fixed value of permeability and to modify the mass conservation equation if there are air voids which are entrapped inside the fiber tow. Finally, we also suggest some guidelines and future perspectives to obtain more consistent permeability measurement results.

Characterization of transient through-thickness permeabilities of Non Crimp New Concept (NC2) multiaxial fabrics

In order to support the development of the recent composite manufacturing processes involving resin infusion across dry preforms prior to cure, a big effort has been realized to obtain reliable experimental techniques for measuring the through-thickness permeability. Some of our previous works focused on the through-thickness permeability measured in saturated regime for some so-called Non Crimped New Concept (NC2) multiaxial fabrics [Drapier S, Pagot A, Vautrin A, Henrat P. Influence of the stitching density on the transverse permeability of non-crimped new concept (NC2) multiaxial reinforcements: measurements and predictions. Compos Sci Technol 2002;62(15):1979-1991; Elbouazzaoui O, Drapier S, Henrat P. An experimental assessment of the saturated transverse permeability in Non Crimp New Concept (NC2) multiaxial fabrics. To appear in J Compos Mater]. But since in the real processes, both saturated and transient permeabilities are encountered, experimental assessments of these two permeabilities has to be achieved. If in saturated regime the through-thickness permeability is relatively easy to assess, in transient regime, however, the flow front is hardly defined in such small dimensions (order of 1 mm). Relying on optical fibre sensors to detect the flow front, transient through-thickness permeabilities are assessed here for various fibre volume fractions. using a Darcy's law to deduce the permeability from the fluid pressure and velocity. These measurements exhibit a satisfying reproducibility and appear to be consistent with the saturated permeabilities, in the sense that here again the permeability measured depends on the face receiving the fluid [Elbouazzaoui O, Drapier S, Henrat P. An experimental assessment of the saturated transverse permeability in Non Crimp New Concept (NC2) multiaxial fabrics. To appear in J Compos Mater]. Moreover, the transient permeabilities appear to be around a factor 10 larger than the saturated permeabilities. Since the differentiation between saturated and transient permeabilities is an open problem, these experimental results can be used for some process simulations as well as a basis for some theoretical developments of the permeability prediction in both regimes.

Environments of Formation and Controls on Spatial Distribution of Calcite Cementation in Plio-Pleistocene Fluvial Deposits, New Mexico, U.S.A.

ABSTRACT The Sierra Ladrones Formation is the uppermost syn-rift sedimentary unit of the Rio Grande Rift in central New Mexico. In the vicinity of the study site it was deposited in a variety of fluvial subenvironments. Portions of the Formation are strongly cemented by calcite, forming resistant ledges in otherwise poorly consolidated sediment. The calcite exhibits a wide range of macroscopic and microscopic textures and structures, which formed in different hydrologic environments, including vadose nonpedogenic, vadose pedogenic, and phreatic. Phreatic cements are characterized by sparite with uniform, disseminated, isopachous, poikilotopic, and drusy textures; vadose-nonpedogenic by micrite with meniscus textures; and vadose-pedogenic by textures similar to those in the vadose-nonpedogenic environment, plus macroscopic features such as root structures, destruction of primary sedimentary textures, and a red hue. Many of the cements are of mixed vadose/phreatic origin, with vadose micrite formation preceding phreatic sparite. The calcite is near end-member in composition, with only minor substitution of trace elements (Sr, Mg, Mn, and Fe) for Ca in the calcite structure. Vadose micrite cements generally have a higher trace-element content than phreatic sparite, perhaps as a result of more rapid precipitation in the vadose zone. Carbon isotope values range from -4.7 to -3.5‰ PDB and 18O values range from -10.3 to -7.2‰ PDB. Cements that are dominantly vadose have a wider range of 13C values, and are more 13C-depleted overall than phreatic cements. Oxygen values are similar for both vadose and phreatic cements. At large scales (i.e., several meters to decameters vertical dimension), calcite is present preferentially in coarse-grained sediments that had high pre-cementation saturated permeabilities relative to uncemented finer-grained strata. At smaller scales (i.e., several meters or less vertical dimension), however, there is no clear relationship between degree of cementation and pre-cementation permeability. At these scales, calcite cement is present preferentially in areas that contain early vadose calcite. This suggests that at large scales cementation was controlled by pre-cementation permeability, perhaps due to a greater flux of Ca2+ and/or HCO3- in permeable horizons, whereas at smaller scales, within high permeability units, the distribution of cementation was controlled by other factors, such as the presence of nucleating material.

Pore-scale modeling of saturated permeabilities in random sphere packings.

We use two pore-scale approaches, lattice-Boltzmann (LB) and pore-network modeling, to simulate single-phase flow in simulated sphere packings that vary in porosity and sphere-size distribution. For both modeling approaches, we determine the size of the representative elementary volume with respect to the permeability. Permeabilities obtained by LB modeling agree well with Rumpf and Gupte's experiments in sphere packings for small Reynolds numbers. The LB simulations agree well with the empirical Ergun equation for intermediate but not for small Reynolds numbers. We suggest a modified form of Ergun's equation to describe both low and intermediate Reynolds number flows. The pore-network simulations agree well with predictions from the effective-medium approximation but underestimate the permeability due to the simplified representation of the porous media. Based on LB simulations in packings with log-normal sphere-size distributions, we suggest a permeability relation with respect to the porosity, as well as the mean and standard deviation of the sphere diameter.

Permeability characterization. Part 2: Flow behavior in multiple‐layer preforms

AbstractWithin the resin transfer molding (RTM) process, flow is generally characterized by the progression of a distinct, nonuniform flow front into the preform as a function of time. The flow front progression introduces unsaturated characteristics into RTM flow fields. As a result, the definition of an effective in‐plane permeability (Keff) is used to determine the permeability of actual preforms as they fill with fluid. This Keff expression expands upon the original definition of Darcy's law by generalizing its applicability to unsaturated creeping flows. Results of experimentally obtained Keff for flow in single‐layer preforms have been detailed for two common RTM materials, a random mat and a 3‐D weave, in Part 1. In this paper (Part 2), we characterize the unsaturated and saturated permeabilities of multiple‐layer preforms constructed from the random mat and 3‐D weave materials characterized in Part 1. This work identifies the apparent permeability characteristics of a specific unsaturated multiple‐layer flow that demonstrates behavior inherent to this important class of heterogeneous flows. Also, parallels are drawn between the unsaturated permeability behavior of complex 3‐D weave materials and multiple‐layer preforms.