scholarly journals Conceptual Hydraulic Conductivity Model for Unsaturated Soils at Low Degree of Saturation and Its Application to the Study of Capillary Barrier Systems

2020 ◽  
Vol 146 (10) ◽  
pp. 04020106
Author(s):  
Riccardo Scarfone ◽  
Simon J. Wheeler ◽  
Marti Lloret-Cabot
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Degree Of Saturation ◽  
Capillary Barrier ◽  
Conductivity Model ◽  
Low Degree

Suction Stress in Unsaturated Soils Considering Hydraulic Hysteresis

2020 ◽  
pp. 110-123
Author(s):  
J. Ramírez Jiménez ◽  
J. M. Horta Rangel ◽  
M. L. Pérez Rea ◽  
E. Rojas González ◽  
T. Lopez Lara ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Time Lag ◽  
Degree Of Saturation ◽  
Soil Suction ◽  
Two Dimensional ◽  
Suction Stress ◽  
Hydraulic Hysteresis ◽  
Transient Thermal ◽  
Over Time

Aims: To develop a flow-moisture model that allows determining the variation of suction over time, as well as the suction stresses, using the finite element method in a two-dimensional model of unsaturated soil through an analogy with a transient thermal problem. Study Design: The variables used in this study were soil suction, hydraulic conductivity, diffusivity and degree of saturation which was represented as the  parameter of the Bishop’s effective stress equation. Place and Duration of Study: Graduate Engineering Department, Universidad Autónoma de Querétaro, between November 2019 and August 2020. Methodology: To establish the model, experimental Soil-Water Retention Curve was taken from Galaviz (2016). With this information, the curves of hydraulic conductivity and diffusivity were calculated with the methods of Fredlund et al. (2012) and Li (1996). In ANSYS 19.2, an analogous transient thermal analysis was run to determine suction changes over time in a 12 x 2.4 meters two-dimensional medium with an impermeable membrane at the center of its surface which was 4.8 meters long. Through these suction changes, the hydraulic hysteresis algorithm presented by Zhou et al. (2012) was used to calculate the respective degrees of saturation, which were considered as the  parameter to obtain the suction stresses. Results: The changes in soil suction, degree of saturation and suction stress were properly modeled. Conclusion: When considering the hydraulic hysteresis cycles, both spatial and temporal variations behaved in a similar way in the  parameters as well as in the suction stresses. Such stresses depended on the analysis period, increasing in the dry season, according to the precipitation-evapotranspiration model, and decreasing in the wetting season. A time lag was observed between the maximum and minimum stresses as greater depths were studied. Along the horizontal axis, considering the same depth, the stresses varied more in the areas adjacent to the impermeable membrane, while at the center this variation was practically null.

Unsaturated flow in coarse porous media

2005 ◽  
Vol 42 (1) ◽  
pp. 252-262 ◽  
Author(s):  
Jeff R Reinson ◽  
Delwyn G Fredlund ◽  
G Ward Wilson
Keyword(s):  
Porous Media ◽  
Hydraulic Conductivity ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Unsaturated Flow ◽  
Characteristic Curve ◽  
Matric Suction ◽  
Coarse Grained ◽  
Capillary Barrier ◽  
Coarse Porous Media

Design of effective capillary barrier systems requires a thorough understanding of the soil–water interactions that take place in both coarse- and fine-grained unsaturated soils. Experimental observations of water flow through coarse porous media are presented to gain greater understanding of the processes and mechanisms that contribute to the movement and retention of water in coarse-grained unsaturated soils. The use of pendular ring theory to describe how water is held within a porous material with relatively low volumetric water contents is explored. Experimental measurements of seepage velocity and volumetric water content were obtained for columns of 12 mm glass beads using digital videography to capture the movement of a dye tracer front at several infiltration rates. An estimated curve for hydraulic conductivity versus matric suction is shown and compared to a theoretical curve. The method is shown to provide a reasonable predictive tool.Key words: soil-water characteristic curve, hydraulic conductivity curve, water permeability function, capillary barrier, matric suction.

Controls on induced polarization in sandy unconsolidated sediments and application to aquifer characterization

Geophysics ◽  
2003 ◽  
Vol 68 (5) ◽  
pp. 1547-1558 ◽  
Author(s):  
L. D. Slater ◽  
D. R. Glaser
Keyword(s):  
Grain Size ◽  
Hydraulic Conductivity ◽  
Internal Surface ◽  
Ionic Mobility ◽  
Induced Polarization ◽  
Hysteretic Behavior ◽  
Degree Of Saturation ◽  
Unconsolidated Sediments ◽  
Fluid Conductivity ◽  
Grain Diameter

Resistivity and induced polarization (IP) measurements (0.1–1000 Hz) were made on clay‐free unconsolidated sediments from a sandy, alluvial aquifer in the Kansas River floodplain. The sensitivity of imaginary conductivity σ″, a fundamental IP measurement, to lithological parameters, fluid conductivity, and degree of saturation was assessed. The previously reported power law dependence of IP on surface area and grain size is clearly observed despite the narrow lithologic range encountered in this unconsolidated sedimentary sequence. The grain‐size σ″ relationship is effectively frequency independent between 0.1 and 100 Hz but depends on the representative grain diameter used. For the sediments examined here, d90, the grain diameter of the coarsest sediments in a sample, is well correlated with σ″. The distribution of the internal surface in the well‐sorted, sandy sediments investigated here is such that most of the sample weight is likely required to account for the majority of the internal surface. We find the predictive capability of the Börner model for hydraulic conductivity (K)estimation from IP measurements is limited when applied to this narrow lithologic range. The relatively weak dependence of σ″ on fluid conductivity (σw) observed for these sediments when saturated with an NaCl solution (0.06–10 S/m) is consistent with competing effects of surface charge density and surface ionic mobility on σ″ as previously inferred for sandstone. Importantly, IP parameters are a function of saturation and exhibit hysteretic behavior over a drainage and imbibition cycle. However, σ″ is less dependent than the real conductivity σ′ on saturation. In the case of evaporative drying, the σ″ saturation exponent is approximately half of the σ′ exponent. Crosshole IP imaging illustrates the potential for lithologic discrimination of unconsolidated sediments. A fining‐upward sequence correlates with an upward increase in normalized chargeability Mn, a field IP parameter proportional to σ″. The hydraulic conductivity distribution obtained from the Börner model discriminates a hydraulically conductive sand–gravel from overlying medium sand.

Capillary-based effective stress formulation for predicting shear strength of unsaturated soils

2015 ◽  
Vol 52 (12) ◽  
pp. 2067-2076 ◽  
Author(s):  
Jean-Marie Konrad ◽  
Marc Lebeau
Keyword(s):  
Shear Strength ◽  
Effective Stress ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Adsorbed Water ◽  
Soil Strength ◽  
Liquid Films ◽  
Degree Of Saturation ◽  
Stress Parameter ◽  
Effective Stress Parameter

A number of investigations have shown that the shear strength of unsaturated soils can be defined in terms of effective stress. The difficulty in this approach lies in quantifying the effective stress parameter, or Bishop’s parameter. Although often set equal to the degree of saturation, it has recently been suggested that the effective stress parameter should be related to an effective degree of saturation, which defines the fraction of water that contributes to soil strength. A problematic element in this approach resides in differentiating the water that contributes to soil strength from that which does not contribute to soil strength. To address this difficulty, the paper uses theoretical considerations and experimental observations to partition the water retention function into capillary and adsorptive components. Given that the thin liquid films of adsorbed water should not contribute to effective stress, the effective stress parameter is solely related to the capillary component of water retention. In sample calculations, this alternative effective stress parameter provided very good agreement with experimental data of shear strength for a variety of soil types.

Simulating transient infiltration in unsaturated soils

1998 ◽  
Vol 35 (6) ◽  
pp. 1093-1100 ◽  
Author(s):  
J R McDougall ◽  
I C Pyrah
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Flow Model ◽  
Unsaturated Flow ◽  
Surface Region ◽  
Infiltration Rate ◽  
Soil Suction ◽  
Wetting Front ◽  
Near Surface ◽  
Unsaturated Hydraulic Conductivity

Transient responses to various infiltration events have been examined using an unsaturated flow model. Numerical simulations reveal a range of infiltration patterns which can be related to the ratio of infiltration rate to unsaturated hydraulic conductivity. A high value of this ratio reflects a prevailing hydraulic conductivity which cannot readily redistribute the newly infiltrated moisture. Moisture accumulates in the near-surface region before advancing down through the soil as a distinct wetting front. In contrast, low values of the ratio of rainfall to unsaturated hydraulic conductivity show minimal moisture accumulation, as the relatively small volumes of infiltrating moisture are readily redistributed through the soil profile.Key words: numerical modelling, infiltration, unsaturated soil, soil suction, groundwater.

Entrapment, stability, and persistence of air bubbles in soil water

Soil Research ◽  
1969 ◽  
Vol 7 (2) ◽  
pp. 79 ◽  
Author(s):  
AJ Peck
Keyword(s):  
Hydraulic Conductivity ◽  
Moisture Content ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Equilibration Time ◽  
Air Bubbles ◽  
Air Entrapment ◽  
Water Characteristics ◽  
Spherical Bubbles ◽  
Entrapped Air

Air bubbles in soil water affect both hydraulic conductivity and moisture content at a given capillary potential. Consequently changes in the volume of entrapped air, which are not included in the specification of relationships between hydraulic conductivity, moisture content, and capillary potential, will affect all soil-water interactions. Current understanding of the process of air bubble entrapment during infiltration suggests that, in nature, significant air entrapment will often occur. It is shown that infiltrating water can dissolve only a very small volume of air, much less than the amount usually entrapped. Air bubbles in saturated soils are unstable since their pressure must exceed atmospheric, resulting in a diffusive flux of dissolved air from bubbles to menisci contacting the external atmosphere. However, stable bubbles are possible in unsaturated soils. Bubbles which are constrained by pore architecture to non-spherical shapes are usually stable, and spherical bubbles can be stable when the magnitude of the capillary potential exceeds about 3 bars. An approximate analysis of the characteristic time of bubble equilibration indicates that, in an example, it is of order 104 sec, but it may be greater or less by at least a factor 10. Since the equilibration time will be often at least as large as the period of significant soil temperature changes, it cannot be assumed that the entrapped air in a field soil is in an equilibrium state. In such circumstances unstable bubbles may be quasi-permanent. It is suggested that the slow growth of entrapped bubbles may account for the anomalously slow release of water observed in some outflow experiments. Changes of entrapped air volume may also account for the reported dependence of soil-water characteristics on the magnitude of the steps of capillary potential.

scholarly journals Impact of the moisture content in medium sands on CPTU test results

2016 ◽  
Vol 48 (3) ◽  
pp. 221-231 ◽  
Author(s):  
Łukasz Zawadzki ◽  
Marek Bajda
Keyword(s):  
Moisture Content ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Degree Of Saturation ◽  
Test Results ◽  
Time Dynamic ◽  
Tip Resistance ◽  
The Impact ◽  
Resistance Value

Abstract Soils occurring in the soil “active zone” are in contact with the surface and are directly influenced by external factors (mainly climatic changes) that cause variation in their parameters over time. Dynamic and uncontrolled changes of soil properties e.g. due to rainfall and evapotranspiration processes may affect field test results leading to the misinterpretation of the obtained data. This paper presents investigations on the influence of moisture content changes in sandy soils on CPTU results. For this purpose, a field ground model has been constructed and five CPTU tests with a different moisture content of soil were carried out. During the investigations, the tip resistance (qc), friction on sleeve (fs), and pore water pressure (u2) were measured. Moreover, a TDR probe was applied to determine the distribution of the moisture content in the studied soil columns. Differences between CPT results obtained in saturated and unsaturated soils have been shown. Furthermore, a simple equation to correct the tip resistance value due to the impact of the degree of saturation has been proposed.

Historical development of soil-water physics and solute transport in porous media

2007 ◽  
Vol 7 (1) ◽  
pp. 59-66 ◽  
Author(s):  
D.E. Rolston
Keyword(s):  
Porous Media ◽  
Hydraulic Conductivity ◽  
Solute Transport ◽  
Soil Water ◽  
20Th Century ◽  
Water Flow ◽  
Unsaturated Soils ◽  
Transport Processes ◽  
Transport In Porous Media ◽  
Unsaturated Hydraulic Conductivity

The science of soil-water physics and contaminant transport in porous media began a little more than a century ago. The first equation to quantify the flow of water is attributed to Darcy. The next major development for unsaturated media was made by Buckingham in 1907. Buckingham quantified the energy state of soil water based on the thermodynamic potential energy. Buckingham then introduced the concept of unsaturated hydraulic conductivity, a function of water content. The water flux as the product of the unsaturated hydraulic conductivity and the total potential gradient has become the accepted Buckingham-Darcy law. Two decades later, Richards applied the continuity equation to Buckingham's equation and obtained a general partial differential equation describing water flow in unsaturated soils. For combined water and solute transport, it had been recognized since the latter half of the 19th century that salts and water do not move uniformly. It wasn't until the middle of the 20th century that scientists began to understand the complex processes of diffusion, dispersion, and convection and to develop mathematical formulations for solute transport. Knowledge on water flow and solute transport processes has expanded greatly since the early part of the 20th century to the present.

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