Showing papers on "Hydraulic conductivity published in 2013"

Development of a China Dataset of Soil Hydraulic Parameters Using Pedotransfer Functions for Land Surface Modeling

Abstract: The objective of this study is to develop a dataset of the soil hydraulic parameters associated with two empirical soil functions (i.e., a water retention curve and hydraulic conductivity) using multiple pedotransfer functions (PTFs). The dataset is designed specifically for regional land surface modeling for China. The authors selected 5 PTFs to derive the parameters in the Clapp and Hornberger functions and the van Genuchten and Mualem functions and 10 PTFs for soil water contents at capillary pressures of 33 and 1500 kPa. The inputs into the PTFs include soil particle size distribution, bulk density, and soil organic matter. The dataset provides 12 estimated parameters and their associated statistical values. The dataset is available at a 30 × 30 arc second geographical spatial resolution and with seven vertical layers to the depth of 1.38 m. The dataset has several distinct advantages even though the accuracy is unknown for lack of in situ and regional measurements. First, this dataset utilize...

Influence of soil, land use and climatic factors on the hydraulic conductivity of soil

Abstract: Due to inadequate data support, existing algo- rithms used to estimate soil hydraulic conductivity, K, in (eco)hydrological models ignore the effects of key site fac- tors such as land use and climate and underplay the signifi- cant effects of soil structure on water flow at and near satura- tion. These limitations may introduce serious bias and error into predictions of terrestrial water balances and soil mois- ture status, and thus plant growth and rates of biogeochem- ical processes. To resolve these issues, we collated a new global database of hydraulic conductivity measured by ten- sion infiltrometer under field conditions. The results of our analyses on this data set contrast markedly with those of ex- isting algorithms used to estimate K. For example, saturated hydraulic conductivity,Ks, in the topsoil (< 0.3 m depth) was found to be only weakly related to texture. Instead, the data suggests that Ks depends more strongly on bulk density, or- ganic carbon content and land use. In this respect, organic carbon was negatively correlated withKs, presumably due to water repellency, whileKs at arable sites was, on average, ca. 2-3 times smaller than under natural vegetation, forests and perennial agriculture. The data also clearly demonstrates that clay soils have smaller K in the soil matrix and thus a larger contribution of soil macropores to K at and near saturation.

Hydraulic limits on maximum plant transpiration and the emergence of the safety–efficiency trade‐off

Abstract: Summary � Soil and plant hydraulics constrain ecosystem productivity by setting physical limits to water transport and hence carbon uptake by leaves. While more negative xylem water potentials provide a larger driving force for water transport, they also cause cavitation that limits hydraulic conductivity. An optimum balance between driving force and cavitation occurs at intermediate water potentials, thus defining the maximum transpiration rate the xylem can sustain (denoted as Emax). The presence of this maximum raises the question as to whether plants regulate transpiration through stomata to function near Emax. � To address this question, we calculated Emax across plant functional types and climates using a hydraulic model and a global database of plant hydraulic traits. � The predicted Emax compared well with measured peak transpiration across plant sizes and growth conditions (R= 0.86, P < 0.001) and was relatively conserved among plant types (for a given plant size), while increasing across climates following the atmospheric evaporative demand. The fact that Emax was roughly conserved across plant types and scales with the product of xylem saturated conductivity and water potential at 50% cavitation was used here to explain the safety–efficiency trade-off in plant xylem. � Stomatal conductance allows maximum transpiration rates despite partial cavitation in the xylem thereby suggesting coordination between stomatal regulation and xylem hydraulic characteristics.

Simple consistent models for water retention and hydraulic conductivity in the complete moisture range

Abstract: [1] The commonly used hydraulic models only account for capillary water retention and conductivity. Adsorptive water retention and film conductivity is neglected. This leads to erroneous description of hydraulic properties in the dry range. The few existing models, which account for film conductivity and adsorptive retention are either difficult to use or physically inconsistent. A new set of empirical hydraulic models for an effective description of water dynamics from full saturation to complete dryness is introduced. The models allow a clear partitioning between capillary and adsorptive water retention as well as between capillary and film conductivity. The number of adjustable parameters for the new retention model is not increased compared to the commonly used models, whereas only one extra parameter for quantifying the contribution of film conductivity is required for the new conductivity model. Both models are mathematically simple and thus easy to use in simulation studies. The new liquid conductivity model is coupled with an existing vapor conductivity model to describe conductivity in the complete moisture range. The new models were successfully applied to literature data, which all reach the dry to very dry range and cannot be well described with the classic capillary models. The investigated soils range from pure sands to clay loams. A simulation study with steady-state water transport scenarios shows that neglecting either film or vapor conductivity or both can lead to significant underestimation of water transport at low water contents.

Improvements in Engineering Properties of Soils through Microbial-Induced Calcite Precipitation

Abstract: Microbial-Induced Calcite Precipitation (MICP) has recently emerged as a sustainable technique for soil improvement. This paper aims to study the effectiveness of MICP in improving the shear strength and reducing the hydraulic conductivity of soils. A species of Bacillus group, B. megaterium was used to trigger the calcite precipitation. The experimental variables included soil types (tropical residual soil and sand), soil densities (85%, 90%, and 95% of their respective maximum densities), and treatment conditions (untreated, treated with cementation reagents only, treated with B. megaterium only, and treated with B. megaterium and cementation reagents). The results showed that MICP could effectively improve shear strength and reduce hydraulic conductivity for both residual soil and sand. The improvements, however, varied with soil densities, soil types, and treatment conditions. With MICP treatment, the improvement ratios in shear strength of the residual soil specimens were significantly higher (1.41–2.64) than those of the sand specimens (1.14–1.25). On the contrary, the sand specimens resulted in greater hydraulic conductivity reduction ratios (0.09–0.15) than those of the residual soil specimens (0.26–0.45). These observations can be explained by the particle-particle contacts per unit volume and pore spaces in the soil specimens. Both soil specimens when treated with cementation reagents only exhibited slight alterations in the shear strength (ranging from 1.06–1.33) and hydraulic conductivity (ranging from 0.69–0.95). The results implied that natural calcite forming microorganisms only exist for insignificant amount. The amount of calcite precipitated in the treated residual soil specimens ranged from 1.080% to 1.889%. The increments of calcite content in the treated sand specimens were comparatively higher, ranging from 2.661% to 6.102%. The results from Scanning Electron Microscope (SEM) analysis confirmed the experimental findings.

Combined influence of sulphate and temperature on the saturated hydraulic conductivity of hardened cemented paste backfill

Abstract: This paper presents an experimental study that focuses on the investigation of the coupled effects of temperature and sulphate on the permeability of hardened cemented paste backfill (CPB). Hydraulic conductivity tests and a microstructural analysis are conducted on mature CPBs prepared with various amounts of sulphate (0, 5000, 15,000, and 25,000 ppm) and cured at various temperatures (2 °C, 20 °C, 35 °C, and 50 °C). Important findings and valuable results are gained. It is found that the coupled effects of sulphate and temperature can lead to decrease (i.e. improvement of the environmental performance of CPBs) or increase of the hydraulic conductivity of CPBs. There is competition between the permeability decreasing and increasing factors. The dominant influencing factors depend on the curing temperature and initial sulphate content.

Temperature effects on the swelling pressure and saturated hydraulic conductivity of the compacted GMZ01 bentonite

Abstract: Using a newly developed apparatus, swelling pressure tests and saturated hydraulic conductivity tests on the compacted Gao-Miao-Zi (GMZ01) bentonite with an initial dry density of 1.7 Mg/m3 were conducted at various temperatures. Based on the test results, the mechanisms of influence of temperature on the swelling pressure and saturated hydraulic conductivity were analyzed. Results indicate that swelling pressure increases with the increase in temperature. The swelling pressures measured at 20 and 40 °C are 3.02 and 3.41 MPa, respectively. For a given temperature, the swelling pressure increases rapidly at the beginning of the infiltration process and then reaches a first peak value followed by an intermediate period characterized by a decrease of swelling pressure, well before the clay reaches its full saturation. The saturated hydraulic conductivity of the GMZ01 bentonite also shows an increase with temperature rise. The temperature changing paths (heating or cooling) have no effect on the saturated hydraulic conductivity. Based on the test results, models for prediction of saturated hydraulic conductivity of the compacted GMZ01 bentonite have been developed and verified. It was observed that the model that only considers the temperature effect on water viscosity gives predictions with large deviation from the measured values, moreover, the deviation increases with temperature rise. When considering both the temperature influence on water viscosity and the effective flow cross-sectional area of porous channels, the model can satisfactorily account for the temperature effects.

Hydraulic Conductivity Imaging from 3-D Transient Hydraulic Tomography at Several Pumping/Observation Densities

Abstract: [1] 3-D Hydraulic tomography (3-D HT) is a method for aquifer characterization whereby the 3-D spatial distribution of aquifer flow parameters (primarily hydraulic conductivity, K) is estimated by joint inversion of head change data from multiple partially penetrating pumping tests. While performance of 3-D HT has been studied extensively in numerical experiments, few field studies have demonstrated the real-world performance of 3-D HT. Here we report on a 3-D transient hydraulic tomography (3-D THT) field experiment at the Boise Hydrogeophysical Research Site which is different from prior approaches in that it represents a ‘‘baseline’’ analysis of 3-D THT performance using only a single arrangement of a central pumping well and five observation wells with nearly complete pumping and observation coverage at 1 m intervals. We jointly analyze all pumping tests using a geostatistical approach based on the quasi-linear estimator of Kitanidis (1995). We reanalyze the system after progressively removing pumping and/or observation intervals; significant progressive loss of information about heterogeneity is quantified as reduced variance of the K field overall, reduced correlation with slug test K estimates at wells, and reduced ability to accurately predict independent pumping tests. We verify that imaging accuracy is strongly improved by pumping and observational densities comparable to the aquifer heterogeneity geostatistical correlation lengths. Discrepancies between K profiles at wells, as obtained from HT and slug tests, are greatest at the tops and bottoms of wells where HT observation coverage was lacking.

A water retention curve and unsaturated hydraulic conductivity model for deformable soils: consideration of the change in pore-size distribution

Abstract: This paper presents a hysteretic water retention curve (WRC) and unsaturated hydraulic conductivity model for deformable soils based on the change in pore-size distribution (PSD). The PSD plays a decisive role in the water retention behaviour of soils. Although its evolution during deformation is rather complicated, experimental data showed that the overall shapes and distribution characteristics of the PSD function are not significantly altered. Based on these findings, the PSD function at a deformed state is obtained by horizontal shifting and vertical scaling of the corresponding PSD function at a reference state. On this basis, a hysteretic WRC model is formulated to account for the influences of deformation and hysteresis on the variation of saturation, using seven model parameters with clear physical meanings. The proposed model is then incorporated in the Mualem model to predict the unsaturated hydraulic conductivity for deformable soils, using only one additional parameter. A large number of publi...

Algae influence the hydrophysical parameters of a sandy soil

Abstract: Article history:Received 2 August 2011Received in revised form 31 January 2012Accepted 3 February 2012Available online xxxxKeywords:AlgaeBiological soil crustSoil water repellencySand duneSorptivityHydraulic conductivity Biological soil crusts have a major effect on water flow in soils. Two study sites, located at a pine-forest gladecovered with a biologicalsoil crust, formed the basis of our study. The sand soil atthe surface (Glade soil) wascompared to a control soil (Pure sand) with limited impact of vegetation or organic matter, occurring at50 cm depth beneath a glade area. To assess the influence ofalgae in the biological soil crust on the propertiesof pure sand, a coccal green alga (Choricystis minor), filamentous green alga (Klebsormidium subtile) and stra-menopile alga (Tribonema minus) were isolated from the top layer of glade soil and grown in the lab in Petridishes on sterile pure sand as monoalgal and bialgal (C. minor and K. subtile) crusts for 3, 5, 7, 9, 11, 13, 15, 17,19, and 21 days. Atthe end ofeach growth stage, the hydrophysicalparametersof crusted sand were estimat-ed after drying at 50 °C for 15 h (equivalent to a 3-day hot spell) and compared to the parameters of puresand. The hydrophysical parameters were substantially different between the two surfaces. The glade soilhad an index of water repellency about 18-times that of pure sand and the persistence of water repellencyalmost 54-times that of pure sand. Both sorptivity and hydraulic conductivity in the glade soil were about7% those of the pure sand, respectively. The growth of artificial algal crusts, characterized by an increase inorganic carbon content from 0.16% to 0.33%, resulted in an increase in water drop penetration time of thedried crusts up to 14-times that of the pure sand and a decrease in the water sorptivity of the dried crustsup to 10% that of the pure sand. Whereas K. subtile crusts (both monoalgal and bialgal with C. minor) hadup to a 9% decrease in hydraulic conductivity compared to pure sand, there was no impact of monoalgalC. minor and T. minus crusts on hydraulic conductivity. K. subtile was possibly limited to surface growth,whereas C. minor and T. minus penetrated to depth. Consequently, K. subtile may have clogged the toppores more effectively than the other two strains. The water repellency cessation time increased with anincrease in water drop penetration time for all the dried monoalgal and bialgal crusts used in this study. Agreater impact of K. subtile on the shifts in hydraulic behaviour could influence water capture and storage,potentially decreasing evaporation during dry periods, but enhancing overland flow diminishing leachingduring wet periods.© 2012 Elsevier B.V. All rights reserved.

Effect of fines content and void ratio on the saturated hydraulic conductivity and undrained shear strength of sand–silt mixtures

Abstract: The hydraulic conductivity represents an important indicator parameter in the generation and redistribution of excess pore pressure of sand–silt mixture soil deposits during earthquakes. This paper aims to determine the relationship between the undrained shear strength (liquefaction resistance) and the saturated hydraulic conductivity of the sand–silt mixtures and how much they are affected by the percentage of low plastic fines (finer than 0.074 mm) and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests carried out on samples reconstituted from Chlef river sand with 0, 10, 20, 30, 40, and 50 % non-plastic silt at an effective confining pressure of 100 kPa and two initial relative densities (D r = 20, 91 %) are presented and discussed. It was found that the undrained shear strength (liquefaction resistance) can be correlated to the fines content, intergranular void ratio and saturated hydraulic conductivity. The results obtained from this study reveal that the saturated hydraulic conductivity (k sat) of the sand mixed with 50 % low plastic fines can be, in average, four orders of magnitude smaller than that of the clean sand. The results show also that the global void ratio could not be used as a pertinent parameter to explain the undrained shear strength and saturated hydraulic conductivity response of the sand–silt mixtures.

Use of NMR logging to obtain estimates of hydraulic conductivity in the High Plains aquifer, Nebraska, USA

Abstract: [1] Hydraulic conductivity (K) is one of the most important parameters of interest in groundwater applications because it quantifies the ease with which water can flow through an aquifer material. Hydraulic conductivity is typically measured by conducting aquifer tests or wellbore flow (WBF) logging. Of interest in our research is the use of proton nuclear magnetic resonance (NMR) logging to obtain information about water-filled porosity and pore space geometry, the combination of which can be used to estimate K. In this study, we acquired a suite of advanced geophysical logs, aquifer tests, WBF logs, and sidewall cores at the field site in Lexington, Nebraska, which is underlain by the High Plains aquifer. We first used two empirical equations developed for petroleum applications to predict K from NMR logging data: the Schlumberger Doll Research equation (KSDR) and the Timur-Coates equation (KT-C), with the standard empirical constants determined for consolidated materials. We upscaled our NMR-derived K estimates to the scale of the WBF-logging K(KWBF-logging) estimates for comparison. All the upscaled KT-C estimates were within an order of magnitude of KWBF-logging and all of the upscaled KSDR estimates were within 2 orders of magnitude of KWBF-logging. We optimized the fit between the upscaled NMR-derived K and KWBF-logging estimates to determine a set of site-specific empirical constants for the unconsolidated materials at our field site. We conclude that reliable estimates of K can be obtained from NMR logging data, thus providing an alternate method for obtaining estimates of K at high levels of vertical resolution.

Evaluation of permeability and non-Darcy flow in vuggy macroporous limestone aquifer samples with lattice Boltzmann methods

Abstract: [1] Lattice Boltzmann flow simulations provide a physics-based means of estimating intrinsic permeability from pore structure and accounting for inertial flow that leads to departures from Darcy's law. Simulations were used to compute intrinsic permeability where standard measurement methods may fail and to provide better understanding of departures from Darcy's law under field conditions. Simulations also investigated resolution issues. Computed tomography (CT) images were acquired at 0.8 mm interscan spacing for seven samples characterized by centimeter-scale biogenic vuggy macroporosity from the extremely transmissive sole-source carbonate karst Biscayne aquifer in southeastern Florida. Samples were as large as 0.3 m in length; 7–9 cm-scale-length subsamples were used for lattice Boltzmann computations. Macroporosity of the subsamples was as high as 81%. Matrix porosity was ignored in the simulations. Non-Darcy behavior led to a twofold reduction in apparent hydraulic conductivity as an applied hydraulic gradient increased to levels observed at regional scale within the Biscayne aquifer; larger reductions are expected under higher gradients near wells and canals. Thus, inertial flows and departures from Darcy's law may occur under field conditions. Changes in apparent hydraulic conductivity with changes in head gradient computed with the lattice Boltzmann model closely fit the Darcy-Forchheimer equation allowing estimation of the Forchheimer parameter. CT-scan resolution appeared adequate to capture intrinsic permeability; however, departures from Darcy behavior were less detectable as resolution coarsened.

Hydration and Cation Exchange during Subgrade Hydration and Effect on Hydraulic Conductivity of Geosynthetic Clay Liners

Abstract: Experiments were conducted to evaluate cation exchange during hydration of geosynthetic clay liners (GCLs) used in composite hydraulic barriers and the effect on their hydraulic conductivity. GCLs arranged in a composite barrier configuration were hydrated by contact with moist compacted subgrades (two clays, one silt, and one sand) under a confining stress of 10 kPa for 30 days to 1 year. No measurable exchange occurred in GCLs hydrated for 30 days. For hydration periods longer than 30 days, the exchange increased as the duration of hydration increased. The exchange during subgrade hydration had no measurable effect on the hydraulic conductivity to deionized (DI) water. However, if the GCL was desiccated after hydration, the hydraulic conductivity increased more than 1,000-fold. Dissolution of calcite within the bentonite during permeation with DI water also induced the replacement of sodium by calcium; however, this additional exchange had no measurable effect on the hydraulic conductivity to DI...

Laboratory measurement of hydraulic conductivity functions of two unsaturated sandy soils during drying and wetting processes

Abstract: The importance of applying unsaturated soil mechanics to geotechnical engineering design has been well understood However, the consumption of time and the necessity for a specific laboratory testing apparatus when measuring unsaturated soil properties have limited the application of unsaturated soil mechanics theories in practice Although methods for predicting unsaturated soil properties have been developed, the verification of these methods for a wide range of soil types is required in order to increase the confidence of practicing engineers in using these methods In this study, a new permeameter was developed to measure the hydraulic conductivity of unsaturated soils using the steady-state method and directly measured suction (negative pore-water pressure) values The apparatus is instrumented with two tensiometers for the direct measurement of suction during the tests The apparatus can be used to obtain the hydraulic conductivity function of sandy soil over a low suction range (0-10 kPa) Firstly, the repeatability of the unsaturated hydraulic conductivity measurement, using the new permeameter, was verified by conducting tests on two identical sandy soil specimens and obtaining similar results The hydraulic conductivity functions of the two sandy soils were then measured during the drying and wetting processes of the soils A significant hysteresis was observed when the hydraulic conductivity was plotted against the suction However, the hysteresis effects were not apparent when the conductivity was plotted against the volumetric water content Furthermore, the measured unsaturated hydraulic conductivity functions were compared with predictions using three different predictive methods that are widely incorporated into numerical software The results suggest that these predictive methods are capable of capturing the measured behavior with reasonable agreement

Hydraulic tomography offers improved imaging of heterogeneity in fractured rocks

Abstract: Fractured rocks have presented formidable challenges for accurately predicting groundwater flow and contaminant transport This is mainly due to our difficulty in mapping the fracture-rock matrix system, their hydraulic properties and connectivity at resolutions that are meaningful for groundwater modeling Over the last several decades, considerable effort has gone into creating maps of subsurface heterogeneity in hydraulic conductivity (K) and specific storage (Ss ) of fractured rocks Developed methods include kriging, stochastic simulation, stochastic inverse modeling, and hydraulic tomography In this article, I review the evolution of various heterogeneity mapping approaches and contend that hydraulic tomography, a recently developed aquifer characterization technique for unconsolidated deposits, is also a promising approach in yielding robust maps (or tomograms) of K and Ss heterogeneity for fractured rocks While hydraulic tomography has recently been shown to be a robust technique, the resolution of the K and Ss tomograms mainly depends on the density of pumping and monitoring locations and the quality of data The resolution will be improved through the development of new devices for higher density monitoring of pressure responses at discrete intervals in boreholes and potentially through the integration of other data from single-hole tests, borehole flowmeter profiling, and tracer tests Other data from temperature and geophysical surveys as well as geological investigations may improve the accuracy of the maps, but more research is needed Technological advances will undoubtedly lead to more accurate maps However, more effort should go into evaluating these maps so that one can gain more confidence in their reliability

Shrub Hydropedology: Preferential Water Availability to Deep Soil Layer

Abstract: The complex interactions between shrub traits, soil structure, and soil water dynamics are not well understood yet. This study investigated rainfall partition by C. microphylla L., spatial soil water pattern, soil hydraulic conductivity, and soil macropores to ascertain preferential water flow to deep soil layer by shrub. Results indicated that high variability in throughfall existed within individual shrub stand: average coefficient of variation was 0.36 ± 0.13 for shrub and 0.15 ± 0.13 for interspace grass. Throughfall was less at the center of the shrub patch (30–60% of rainfall) than the outward positions at the edges of the canopy (70–90% of rainfall). Soil water responded differently to rainfall, soil depth, and vegetation type and showed high variability within shrub patches and on the slope. Greater and deeper infiltration was observed beneath C. microphylla L. canopy than interspaces grass after rainfall with large amount and high intensity, suggesting that macropore flow dominated in shrub patches. X-ray CT showed that macroporosity was over six times greater in soil under C. microphylla L. than interspace grass. Soil hydraulic conductivity for shrub at saturation and the pressure heads of −30, −60, and −150 mm were 3, 2, 2.5, and 2 times than those of grass, respectively. Shrub patches had a significant lower bulk density and higher porosity than grass patches at the top 0- to 30-cm depth. Soil hydraulic conductivity was significantly correlated to organic matter content, total N, bulk density, and porosity. This study suggests that rainfall partition by shrub’s canopy and subsurface soil macropores induced by root architecture results in preferential water flow into deep soil layer, which might favor competitive advantages for water by shrubs under arid conditions.

Shoot hydraulic characteristics, plant water status and stomatal response in olive trees under different soil water conditions

Abstract: To evaluate the impact of the amount and distribution of soil water on xylem anatomy and xylem hydraulics of current-year shoots, plant water status and stomatal conductance of mature ‘Manzanilla’ olive trees. Measurements of water potential, stomatal conductance, hydraulic conductivity, vulnerability to embolism, vessel diameter distribution and vessel density were made in trees under full irrigation with non-limiting soil water conditions, localized irrigation, and rain-fed conditions. All trees showed lower stomatal conductance values in the afternoon than in the morning. The irrigated trees showed water potential values around −1.4 and −1.6 MPa whereas the rain-fed trees reached lower values. All trees showed similar specific hydraulic conductivity (K s) and loss of conductivity values during the morning. In the afternoon, K s of rain-fed trees tended to be lower than of irrigated trees. No differences in vulnerability to embolism, vessel-diameter distribution and vessel density were observed between treatments. A tight control of stomatal conductance was observed in olive which allowed irrigated trees to avoid critical water potential values and keep them in a safe range to avoid embolism. The applied water treatments did not influence the xylem anatomy and vulnerability to embolism of current-year shoots of mature olive trees.

Field study of subsurface heterogeneity with steady-state hydraulic tomography.

Abstract: Remediation of subsurface contamination requires an understanding of the contaminant (history, source location, plume extent and concentration, etc.), and, knowledge of the spatial distribution of hydraulic conductivity (K) that governs groundwater flow and solute transport. Many methods exist for characterizing K heterogeneity, but most if not all methods require the collection of a large number of small-scale data and its interpolation. In this study, we conduct a hydraulic tomography survey at a highly heterogeneous glaciofluvial deposit at the North Campus Research Site (NCRS) located at the University of Waterloo, Waterloo, Ontario, Canada to sequentially interpret four pumping tests using the steady-state form of the Sequential Successive Linear Estimator (SSLE) (Yeh and Liu 2000). The resulting three-dimensional (3D) K distribution (or K-tomogram) is compared against: (1) K distributions obtained through the inverse modeling of individual pumping tests using SSLE, and (2) effective hydraulic conductivity (K(eff) ) estimates obtained by automatically calibrating a groundwater flow model while treating the medium to be homogeneous. Such a K(eff) is often used for designing remediation operations, and thus is used as the basis for comparison with the K-tomogram. Our results clearly show that hydraulic tomography is superior to the inversions of single pumping tests or K(eff) estimates. This is particularly significant for contaminated sites where an accurate representation of the flow field is critical for simulating contaminant transport and injection of chemical and biological agents used for active remediation of contaminant source zones and plumes.

A Drying Cake Method for Measuring Suction-Stress Characteristic Curve, Soil–Water-Retention Curve, and Hydraulic Conductivity Function

Abstract: A drying cake (DC) method is invented for measurement of the suction-stress characteristic curve (SSCC), the soil–water-retention curve (SWRC), and the hydraulic conductivity function (HCF) of soils under drying conditions. The DC method employs particle image velocimetry (PIV) technique to acquire digital still images of the radial displacement field of a disk-shaped soil specimen during drying, while the moisture content of the specimen is recorded using an electronic balance. A linear elasticity theory employing the suction-stress-based effective stress in both total and incremental forms is developed to calculate suction stress, suction, and hydraulic conductivity from the moisture-content-dependent displacement fields; thus permitting definition of the SSCC, SWRC, and HCF of a soil. Five different soils, representing a wide spectrum of soil variety from pure sand, to silt and organic silt, to non-swelling and swelling clays are used to illustrate and test the principle and theory, the validity, and applicability of the DC method. Established measurement techniques for the constitutive relationships of unsaturated soils, such as the Tempe cell, constant flow, transient water release and imbibition, and shear-strength relationships were used to validate the DC method. The results from the DC method were found to compare well with those techniques. Repeated DC tests confirm that the results from the test are unique. It is shown that the DC method is superior to other existing methods in: (1) providing simple and accurate data acquisition (involving taking sequential digital still images and monitoring specimen’s moisture content by an electronic balance without use of suction or moisture probe), (2) facilitating fast testing time (in less than one week for the primary drying path of the SSCC, SWRC, and HCF), (3) permitting concurrent measurement of the SSCC, SWRC, and HCF by using one soil sample, and (4) its applicability to all types of soils under wide suction and moisture-content conditions.