Simultaneous measurement of coupled water, heat, and solute transport in unsaturated porous media is made possible with the multi-functional heat pulse probe (MFHPP). The probe combines a heat pulse technique for estimating soil heat properties, water flux, and water content with a Wenner array measurement of bulk soil electrical conductivity (ECbulk). To evaluate the MFHPP, we conducted controlled steady-state flow experiments in a sand column for a wide range of water saturations, flow velocities, and solute concentrations. Flow and transport processes were monitored continuously using the MFHPP. Experimental data were analyzed by inverse modeling of simultaneous water, heat, and solute transport using an adapted HYDRUS-2D model. Various optimization scenarios yielded simultaneous estimation of thermal, solute, and hydraulic parameters and variables, including thermal conductivity, volumetric water content, water flux, and thermal and solute dispersivities. We conclude that the MFHPP holds great promise as an excellent instrument for the continuous monitoring and characterization of the vadose zone. 相似文献
Shallow failures of slopes in weathered soil are caused by infiltration due to prolonged rainfall. These failures are mainly triggered by the deepening of the wetting band accompanied by a decrease in matric suction induced by the water infiltration. This paper reports trends of rainfall-induced wetting band depth in two types of weathered soils that are commonly found in Korea. Both theoretical and numerical analyses for wetting band depth are presented based on the soil–water characteristic curve obtained using filter paper as well as tensiometer tests. It is found that the magnitude of wetting front suction plays a key role in the stability of slopes in weathered soils. Theoretical analysis based on modified Green and Ampt model tends to underestimate the wetting band depth for typical Korean weathered soils. It was also deduced that for Korean weathered soils, the factor of safety drops rapidly once the wetting band depth of 1.2 m reached. 相似文献
Previous studies indicate that a small quantity of recharge occurs from infiltration of streamflow in intermittent streams
in the upper Mojave River basin, in the western Mojave Desert, near Victorville, California. Chloride, tritium, and stable
isotope data collected in the unsaturated zone between 1994 and 1998 from boreholes drilled in Oro Grande and Sheep Creek
Washes indicate that infiltration of streamflow occurs to depths below the root zone, and presumably to the water table, along
much of Oro Grande Wash and near the mountain front along Sheep Creek Wash. Differences in infiltration at sites along each
wash are the result of hydrologic variables such as proximity to the mountain front, quantity of streamflow, and texture of
the subsurface deposits. Differences in infiltration between the washes are the result of large-scale geomorphic processes.
For example, Oro Grande wash is incised into the Victorville fan and infiltration has occurred at approximately the same location
over recent geologic time. In contrast, Sheep Creek Wash overlies an active alluvial fan and the stream channel can move across
the fan surface through time. Infiltration does not occur to depths below the root zone at control sites outside of the washes.
Electronic Publication 相似文献
The hydro-mechanical behaviour of a clay-based buffer material for nuclear waste disposal has been investigated in a laboratory program. In this program, the main focus was on the influence of confinement on water uptake and swelling pressure during suction decrease. The laboratory program and some of the results are presented by Dueck [Dueck, A., 2006. Laboratory results from hydro-mechanical tests on a water unsaturated bentonite. submitted for publication.].
The results from the laboratory tests were used to find a relationship between water content, void ratio, swelling pressure and suction. Two equations for swelling pressure represent the outline of the model.
In the first equation, the swelling pressure developed during water uptake is normalised by a pressure corresponding to the swelling pressure at saturation. This is done in order to be independent of void ratio. A relationship between the normalised swelling pressure and the degree of saturation is suggested.
The second equation describes a relationship between the swelling pressure, the water content and the actual suction (or relative humidity). The equation is based on a thermodynamic relationship and includes the retention curve (i.e. water content vs. suction under free swelling conditions).
The model can be used for a state where two of the four variables; water content, void ratio, swelling pressure and suction are known and can thus be useful to evaluate field measurements and model late stages of the wetting process. An example of an application is given. The equations are mainly based on results from tests with increasing degrees of saturation under constant void ratio but are also suggested for use with increasing void ratio. 相似文献
In this paper, the shear strength with respect to the matric suction of unsaturated soils was studied. For this purpose, unsaturated
triaxial testing procedures were applied to the undisturbed residual soil specimens. An apparatus for performing triaxial
tests was designed and constructed. In the tests, matric suction was controlled by using the axis translation technique, and
pore water volume changes were measured by means of a volume change transducer with 10−8 m3 sensitivity. The test results indicated that the matric suction contributes to the shear strength of unsaturated soil specimens,
and this contribution called suction strength varies non-linearly with respect to the matric suction. The logarithmic model
needing to know the air-entry value and the internal friction angle of a soil specimen for prediction of the suction strength
were presented and compared with the test results. It was found that suction strength values predicted from the proposed model
were in satisfactory agreement with the experimental results. 相似文献
Recharge rates determined at diverse study sites in a shallow, unconfined aquifer differed from one another depending on the
analytical method used and on each method’s applicability and limitations. Total recharge was quantified with saturated-zone
methods using water-table fluctuations at seven sites in North Carolina, USA and using groundwater-age dating at three of
the seven sites; at two of the sites, potential recharge was quantified with an unsaturated-zone method using Darcy’s law;
and at five of the sites, net recharge was quantified with a stream hydrograph-separation method using streamflow-recession
curves. Historical mean net recharge was 25 to 69% of the historical total recharge rates. The large disparity is attributed
to groundwater losses between recharge and discharge areas, primarily by evapotranspiration and seepage to underlying aquifers.
The spatial distribution of historical mean annual total recharge did not vary between landscape units, as suggested in a
previous study. Similarly, total recharge did not correlate significantly with mean annual rainfall, mean annual water table
depth, or the surficial soil properties of percent clay and bulk density. Total recharge did correlate significantly with
the surficial soil properties of percent sand and percent silt.
Résumé Les taux de recharge déterminés sur divers sites d’études dans un aquifère phréatique libre, varient les uns par rapport aux
autres selon la méthode analytique utilisée et les limites et l’applicabilité de chaque méthode. La recharge totale a été
quantifiée avec des méthodes en zone saturée utilisant les fluctuations des nappes sur sept sites de la Caroline du Nord,
USA, et en utilisant les datations des eaux souterraines sur trois des sept sites ; sur deux des sites, la recharge potentielle
a été quantifiée avec une méthode en zone non-saturée utilisant la loi de Darcy, et sur deux sites, la recharge nette a été
quantifiée suivant une méthode de séparation des hydrographes de cours d’eau utilisant les courbes de récession du débit.
La moyenne historique de la recharge nette est comprise entre 25 et 69% des taux historiques de recharge totale. L’importante
disparité est attribuée aux pertes en eaux souterraines entre les zones de recharge et les zones d’exutoire, d’abord par évapotranspiration
et ensuite par infiltration vers les aquifères sous-jacents. La distribution spatiale de la recharge historique moyenne annuelle
et totale ne varie pas selon les unités paysagères, comme cela était suggéré dans une étude antérieure. De même, la recharge
totale n’est pas corrélée significativement avec la moyenne annuelle des précipitations, la moyenne annuelle de la profondeur
de la nappe, ou les propriétés de surface des sols que sont le pourcentage d’argile ou la densité apparente. La recharge totale
est corrélée significativement avec les propriétés de surface du sol et les teneurs en sable et en silt.
Resumen Las tasas de recarga determinadas en diversos sitios de estudio en un acuífero somero no confinado difieren entre sí dependiendo
del método analítico usado y de las limitaciones y aplicabilidad de cada método. Se cuantificó la recarga total con métodos
de zona saturada usando fluctuaciones del nivel freático en siete sitios en Carolina del Norte, Estados Unidos, y usando datación
de edades de agua subterránea en tres de los siete sitios; en dos de los sitios se cuantificó la recarga potencial con un
método de zona no saturada usando la Ley de Darcy y en cinco de los sitios se cuantificó la recarga neta con el método de
separación hidrográfica usando curvas de recesión de flujo en arroyos. La recarga neta media histórica varió entre 25 y 69%
de las tasas de recarga total histórica. La diferencia tan grande se atribuye a pérdidas de agua subterránea entre áreas de
descarga y recarga, principalmente por evapotranspiración y escurrimiento hacia acuíferos subyacentes. La distribución espacial
de la recarga total anual media histórica no varió entre las unidades de paisaje, como ya se había sugerido en un estudio
previo. De modo similar, la recarga total no guarda correlación significativa con la lluvia media anual, la profundidad media
anual del nivel freático, o las propiedades superficiales del suelo, particularmente porcentaje de arcilla y densidad volumétrica.
La recarga total si tuvo una correlación significativa con las propiedades superficiales del suelo tal como porcentaje de
arena y porcentaje de limo.