Laboratory Measurements Of Hydraulic Conductivity Research Articles

Fabrication of Permeameter for Determination of Hydraulic Conductivity of Earth Materials

Laboratory investigation is one of the major ways of assessing soil hydraulic conductivity. Determination of hydraulic conductivity aids in engineering design of well pumping, prediction concerning spread of polluting fluids, embankment of canal bank affected by seepage, flooding solutions and stability of earth dams. However, different studies have shown that there are alternative models to Darcy’s law which governs the widely use of laboratory measurement of hydraulic conductivity. The deficiencies accustomed to the conventional permeameter such as the time wastage and cost-intensivehas led to different research modification. A low-cost permeameter was fabricated using a plastic column, hose pipe, to serve as water inlet and outlet connected to two manometer tubes to measure the pressure head difference. The hydraulic conductivities measured using the low-cost were 4.31 cm/s, 8.14 cm/s, 6.12 cm/s, 5.86 cm/s for 0.3 mm coarse sand, 0.85-1 mm fine sand, sandy clay and silty clay respectively. In comparison of the fabricated permeameter with conventional permeameter and other fabricated laboratory permeameters, it was observed that the hydraulic conductivity obtained is consistent with the typical permeability range for each soil type.

Application of fitting parameters in best fit equation

Soil-water characteristic curve (SWCC) contains key information for the application of unsaturated soil mechanics principles to engineering practice. SWCC variables such as air-entry value, residual suction and residual saturation are commonly referred to for estimation of other unsaturated soil properties. Though there are clear definitions for these SWCC variables, it is difficult to measure them directly in laboratory and these SWCC variables are commonly estimated from SWCC. Hydraulic conductivity of unsaturated soil is the major property that controls water flow in soil. The laboratory measurement of hydraulic conductivity is time consuming and costly. Therefore, hydraulic conductivity is also commonly estimated from SWCC. Normally, SWCC is represented by a best fit equation which is typically governed by few fitting parameters. These fitting parameters can be obtained from a best fit procedure and are proven to be dependent on each other. Fredlund and Xing’s (1994) equation is one of the popular equations commonly used by researchers and there are only three fitting parameters such as “a”, “n”, “m” in this equation. Correlation equations between SWCC variables, hydraulic conductivity and the fitting parameters such as “a”, “n” and “m” are presented in this paper. In addition, the variability in the determined SWCC variables and hydraulic conductivity due to the variation in these fitting parameters is also discussed in this paper.

Determining the Effective Hydraulic Properties of a Highly Heterogeneous Soil Horizon

In this study, we have attempted to determine the effective hydraulic properties of a highly heterogeneous soil horizon composed of two elementary pedological volumes (EPVs). Our upscaling approach was guided by the “scaleway” approach, in which the properties of a complex system can be estimated by multiple discrete upscaling steps. This approach was tested on a data set from laboratory measurements of hydraulic conductivity at the EPV scale, while an explicit three‐dimensional soil structure was considered at the horizon scale. We then formulated a decision tree to guide the choice of the appropriate upscaling method to determine the effective hydraulic conductivity at the horizon scale. In the case of low contrast between hydraulic conductivities at the EPV scale, the effective hydraulic conductivity at the horizon scale can be achieved by calculating the Wiener bounds, which requires only the proportion of the different EPVs. In the case of high contrast between hydraulic conductivities at the EPV scale, we recommend either calculating the Cardwell and Parson bounds, or performing a direct three‐dimensional numerical simulation to solve Richards' equation, which requires an explicit representation of the three‐dimensional structure of the soil horizon. The Cardwell and Parsons bounds remains a good and easily available approximation. Otherwise, more accurate estimation can be obtained by numerical simulation, although this is time consuming. A decision map is proposed to help choose the best method to estimate the effective hydraulic conductivity.

Deformation mechanisms and hydraulic properties of fault zones in unconsolidated sediments; the Roer Valley Rift System, The Netherlands

In general, faults cutting through the unconsolidated sediments of the Roer Valley Rift System (RVRS), The Netherlands, form strong barriers to horizontal groundwater flow. The relationships between deformation mechanisms along fault zones and their impact on the hydrogeological structure of the fault zone are analyzed in a shallow (0–5 m below land surface) trench over one of the faults in the study area. Recently developed digital-image-analysis techniques are used to estimate the spatial distribution of hydraulic conductivity at the millimeter-scale and to describe the micromorphologic characteristics of the fault zone. In addition, laboratory measurements of hydraulic conductivity on core-plug samples show the larger-scale distribution of hydraulic conductivity in the damage zone flanking the main fault plane. Particulate flow is the deformation mechanism at shallow depths, which causes the damage zone around the fault, in the sand-rich parts, to have a relatively enhanced hydraulic conductivity. The fault core is characterized by reduced hydraulic conductivity due to clay smearing, grain-scale mixing, and iron-oxide precipitation.

Predictive modeling of flow and transport in a two‐dimensional intermediate‐scale, heterogeneous porous medium

As a first step toward understanding the role of sedimentary structures in flow and transport through porous media, this work deterministically examines how small‐scale laboratory‐measured values of hydraulic conductivity relate to in situ values of simple, artificial structures in an intermediate‐scale (10 m long), two‐dimensional, heterogeneous, laboratory experiment. Results were judged based on how well simulations using measured values of hydraulic conductivities matched measured hydraulic heads, net flow, and transport through the tank. Discrepancies were investigated using sensitivity analysis and nonlinear regression estimates of the in situ hydraulic conductivity that produce the best fit to measured hydraulic heads and net flow. Permeameter and column experiments produced laboratory measurements of hydraulic conductivity for each of the sands used in the intermediate‐scale experiments. Despite explicit numerical representation of the heterogeneity the laboratory‐measured values underestimated net flow by 12–14% and were distinctly smaller than the regression‐estimated values. The significance of differences in measured hydraulic conductivity values was investigated by comparing variability of transport predictions using the different measurement methods to that produced by different realizations of the heterogeneous distribution. Results indicate that the variations in measured hydraulic conductivity were more important to transport than variations between realizations of the heterogeneous distribution of hydraulic conductivity.

Hydraulic Conductivity of Soils from Grain-Size Distribution: New Models

This paper presents new developments of regression-based models to predict the saturated hydraulic conductivity of compacted soils from grain-size distribution. The models incorporate parameter values that adequately represent the distribution of grain sizes. Alternative representations of the grain-size distribution, the fractal dimension and entropy of the distributions, as well as porosity, soil density, and fines content are used in the models to estimate the hydraulic conductivity. These parameters that characterize the textural and hydraulic properties of the soil are combined and used in a multidimensional analysis to estimate the hydraulic conductivity. The predictions of the developed models are compared with those of existing models and laboratory measurements of hydraulic conductivity. The results suggest that the newly developed models outperform the existing models in predicting hydraulic conductivity using information from grain-size distribution. The presented models are suggested as alternatives to, for example, laboratory measurements of the hydraulic conductivity of certain soils that may be difficult to prepare or that may take several days or perhaps weeks to perform. In certain circumstances it may also be used to give first-hand information about the hydraulic properties in a field environment.

Laboratory measurement of fine-grained soil fluid conductivity

Advective fluid flow, which depends directly on hydraulic conductivity, controls contaminant migration through soils in many cases. The state of practice in laboratory measurements of hydraulic conductivity of soils was reviewed and found to be extremely variable, with the result that measurements on a given soil material often give variations of several orders of magnitude. An experimental program was completed using compacted clay soils to study several facets of laboratory testing practice, and a suitable test procedure for consistent results was developed. Recommendations on several important aspects of procedure are presented.

Fluid Conductivity Testing of Fine‐Grained Soils

Advective fluid flow, which depends directly on hydraulic conductivity, controls contaminant migration through soils in many cases. The state of practice in laboratory measurements of hydraulic conductivity of soils was reviewed and found to be extremely variable, with the result that measurements on a given soil material often give variations of several orders of magnitude. An experimental program was completed using compacted clay soils to study several facets of laboratory testing practice, and a suitable test procedure for consistent results was developed. Recommendations on several important aspects of procedure are presented. The procedure was also evaluated with a synthetic lead‐zinc tailings leachate, and alteration of the test soils' hydraulic conductivity was evaluated and correlated with probable chemical interactions of the test permeants and soils.