A Theoretical Study of Some Unsaturated Properties for Different Soils

2018 ◽  
Vol 26 (9) ◽  
pp. 149-165
Author(s):  
Mohammed Nawaf Jirjees Alzaidy
Keyword(s):  
Shear Strength ◽  
Hydraulic Conductivity ◽  
Water Content ◽  
Unsaturated Soil ◽  
Basic Relation ◽  
Soil Suction ◽  
Unsaturated Hydraulic Conductivity ◽  
Clayey Silt ◽  
Two Parameters ◽  
Different Soils

Soil–water characteristic curves (SWCC) can be defined as the relationship between the water content and suction of an unsaturated soil. It considered a basic relation to explanation of the engineering behaviour of unsaturated soil such as hydraulic conductivity and shear strength, So the study of SWCC is useful to reduce the time and cost of unsaturated soil testing for different engineering purposes. An approach model has been used to predict the SWCC for different soils. The influence of the soils on SWCC shape, the unsaturated hydraulic conductivity and shear strength parameters have been studied in this paper using mathematical models. The results of SWCC show that suction of clay soil is bigger than sandy soil, while the clayey silt soils exhibit an intermediate behaviour at same water content. The values of unsaturated shear strength are increasing while the unsaturated hydraulic conductivity is decreasing with increasing soil suction. This behaviour of the last two parameters with soil suction should be taken in consideration for engineering purposes.

Estimation of hydraulic conductivity of unsaturated soils using a geotechnical centrifuge

2002 ◽  
Vol 39 (3) ◽  
pp. 684-694 ◽  
Author(s):  
D N Singh ◽  
Sneha J Kuriyan
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Sample ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Hydraulic Conductivity ◽  
Centrifuge Testing ◽  
Geotechnical Centrifuge ◽  
Silty Soil ◽  
Unsaturated Hydraulic Conductivity

A saturated silty soil sample is centrifuged in a geotechnical centrifuge to create an unsaturated state. The change in water content of the soil sample is recorded at different points along the length of the sample to obtain the water-content profile, which is then used to obtain the unsaturated hydraulic conductivity of the soil sample. These hydraulic conductivity values are compared with those obtained and reported by previous researchers by conducting accelerated falling-head tests on this soil sample in a centrifuge. The study demonstrates the use of centrifugation techniques to obtain hydraulic conductivities of unsaturated soils.Key words: silty soil, saturated soil, unsaturated soil, hydraulic conductivity, centrifuge testing.

Estimation of unsaturated hydraulic conductivity using soil suction measurements obtained by an insertion tensiometer

2003 ◽  
Vol 40 (2) ◽  
pp. 476-483 ◽  
Author(s):  
D N Singh ◽  
Sneha J Kuriyan
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Characteristic Curve ◽  
Soil Suction ◽  
Soil Hydraulic Conductivity ◽  
Silty Soil ◽  
Soil Water Characteristic Curve ◽  
Unsaturated Hydraulic Conductivity ◽  
Soil Hydraulic

To estimate the unsaturated soil hydraulic conductivity of a silty soil, an insertion tensiometer has been used for measuring its suction corresponding to different water contents. These suction values have been used for developing the soil-water characteristic curve (SWCC). The obtained SWCC has been compared with the trends predicted by various fits available in the literature. Further, with the help of the obtained SWCC, the unsaturated soil hydraulic conductivity has been estimated. The study demonstrates the usefulness of insertion tensiometers for measuring soil suction and for estimating its hydraulic conductivity.Key words: silty soil, suction, insertion tensiometer, soil-water characteristic curve, unsaturated soil hydraulic conductivity.

Hyphal colonization of Rhizophagus irregularis increases unsaturated hydraulic conductivity of a loamy sand distant from roots

2021 ◽  
Author(s):  
Michael Bitterlich ◽  
Richard Pauwels
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Hydraulic Properties ◽  
Volumetric Water Content ◽  
Rhizophagus Irregularis ◽  
Loamy Sand ◽  
Soil Hydraulic Properties ◽  
Unsaturated Hydraulic Conductivity ◽  
Soil Hydraulic ◽  
Root Exclusion

<p>Hydraulic properties of mycorrhizal soils have rarely been reported and difficulties in directly assigning potential effects to hyphae of arbuscular mycorrhizal fungi (AMF) arise from other consequences of AMF being present, i.e. their influence on growth and water consumption rates of their host plants that both also influence soil hydraulic properties.</p><p>We assumed that the typical nylon meshes used for root-exclusion experiments in mycorrhizal research can provide a dynamic hydraulic barrier. It is expected that the uniform pore size of the rigid meshes causes a sudden hydraulic decoupling of the enmeshed inner volume from the surrounding soil as soon as the mesh pores become air-filled. Growing plants below the soil moisture threshold for hydraulic decoupling would minimize plant-size effects on root-exclusion compartments and allow for a more direct assignment of hyphal presence to modulations in soil hydraulic properties.</p><p>We carried out water retention and hydraulic conductivity measurements with two tensiometers introduced in two different heights in a cylindrical compartment (250 cm³) containing a loamy sand, either with or without the introduction of a 20 µm nylon mesh equidistantly between the tensiometers. Introduction of a mesh reduced hydraulic conductivity across the soil volumes by two orders of magnitude from 471 to 6 µm d<sup>-1</sup> at 20% volumetric water content.</p><p>We grew maize plants inoculated or not with Rhizophagus irregularis in the same soil in pots that contained root-exclusion compartments while maintaining 20% volumetric water content. When hyphae were present in the compartments, water potential and unsaturated hydraulic conductivity increased for a given water content compared to compartments free of hyphae. These differences increased with progressive soil drying.</p><p>We conclude that water extractability from soils distant to roots can be facilitated under dry conditions when AMF hyphae are present.</p><p> </p>

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.

Determination of hydraulic conductivity as a function of depth and water content for soil in situ

Soil Research ◽  
1965 ◽  
Vol 3 (1) ◽  
pp. 1 ◽  
Author(s):  
CW Rose ◽  
WR Stern ◽  
JE Drummond
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Soil Profile ◽  
Saturated Soil ◽  
Potential Gradients

A theory is presented to calculate hydraulic conductivity from successive measurements of water content profiles for soil in situ. With unsaturated soil, potential gradients are inferred using moisture characteristics, but with saturated soil these gradients must be measured directly. The weight of overburden can affect in situ soil water suction, and a method for determining this effect is given. The theory was applied to a soil profile with marked changes in moisture characteristics and texture, and conductivity was determined for several depths as a function of water content.

Model for the prediction of shear strength with respect to soil suction

1996 ◽  
Vol 33 (3) ◽  
pp. 379-392 ◽  
Author(s):  
S K Vanapalli ◽  
D G Fredlund ◽  
D E Pufahl ◽  
A W Clifton
Keyword(s):  
Shear Strength ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Experimental Studies ◽  
Matric Suction ◽  
Glacial Till ◽  
Soil Suction ◽  
Soil Water Characteristic Curve

Experimental studies on unsaturated soils are generally costly, time-consuming, and difficult to conduct. Shear strength data from the research literature suggests that there is a nonlinear increase in strength as the soil desaturates as a result of an increase in matric suction. Since the shear strength of an unsaturated soil is strongly related to the amount of water in the voids of the soil, and therefore to matric suction, it is postulated that the shear strength of an unsaturated soil should also bear a relationship to the soil-water characteristic curve. This paper describes the relationship between the soil-water characteristic curve and the shear strength of an unsaturated soil with respect to matric suction. Am empirical, analytical model is developed to predict the shear strength in terms of soil suction. The formulation makes use of the soil-water characteristic curve and the saturated shear strength parameters. The results of the model developed for predicting the shear strength are compared with experimental results for a glacial till. The shear strength of statically compacted glacial till specimens was measured using a modified direct shear apparatus. Specimens were prepared at three different water contents and densities (i.e., corresponding to dry of optimum, and wet of optimum conditions). Various net normal stresses and matric suctions were applied to the specimens. There is a good correlation between the predicted and measured values of shear strength for the unsaturated soil. Key words: soil-water characteristic curve, shear strength, unsaturated soil, soil suction, matric suction.

scholarly journals Spatial distribution of argan tree influence on soil properties in southern Morocco

SOIL ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 511-524
Author(s):  
Mario Kirchhoff ◽  
Tobias Romes ◽  
Irene Marzolff ◽  
Manuel Seeger ◽  
Ali Aït Hssaine ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Seedling Survival ◽  
Drip Line ◽  
Soil Parameters ◽  
Wind Drift ◽  
Argan Tree ◽  
Unsaturated Hydraulic Conductivity

Abstract. The endemic argan tree (Argania spinosa) populations in southern Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth; however, it is unknown if the trees influence the soil of the intertree areas. Hypothetically, spatial differences in soil parameters of the intertree area should result from the translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. In total, 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) and the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) up to 50 m distance from the tree. They were analysed for gravimetric soil water content, pH, electrical conductivity, percolation stability, total nitrogen content (TN), content of soil organic carbon (SOC) and C/N ratio. A total of 74 tension disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity. We found that the tree influence on its surrounding intertree area is limited, with, e.g., SOC and TN content decreasing significantly from tree trunk (4.4 % SOC and 0.3 % TN) to tree drip line (2.0 % SOC and 0.2 % TN). However, intertree areas near the tree drip line (1.3 % SOC and 0.2 % TN) differed significantly from intertree areas between two trees (1.0 % SOC and 0.1 % TN) yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil water content was highest in the north due to shade from the midday sun; the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line. This was the case on sites under different land usages (silvopastoral and agricultural), slope gradients or tree densities. Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should be aimed around tree shelters in northern or eastern directions with higher soil water content or TN or SOC content to ensure seedling survival, along with measures to prevent overgrazing.

Finite formulation for the computation of sorptivity

2020 ◽  
Author(s):  
Pierre-Emmanuel Peyneau ◽  
Laurent Lassabatere ◽  
Joseph Pollacco ◽  
Jesús Fernández-Gálvez ◽  
Borja Latorre ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Water Retention ◽  
Water Pressure ◽  
Pressure Head ◽  
Concentration Function ◽  
Point Of View ◽  
Water Infiltration ◽  
Unsaturated Hydraulic Conductivity ◽  
Flux Concentration

<p>Soil sorptivity is one of the key hydraulic parameters for modelling water infiltration into soil. It quantifies the capacity of a soil to infiltrate water by capillarity. Several formulations, based on various models, have been proposed to compute it from the water retention and the unsaturated hydraulic conductivity functions. All these formulations use the integration of the product of either the hydraulic conductivity or diffusivity function with the flux concentration function. The integration can be performed either over an interval of water pressure head or water content, yielding two equal values. However, the expression of the integral as a function of water pressure head may involve a huge or even infinite interval, which can be numerically difficult to handle. In opposite, the expression of the integral as a function of water content involves the integration of a diverging function (diffusivity) over a large interval, which is also troublesome from a numerical point of view. In this paper, we provide a new expression for sorptivity by cutting the integral in two parts, in order to involve only the integration of a finite function over a finite interval. The dependency of the integral on the flux concentration function is also investigated.</p>

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