scholarly journals Definition and experimental determination of a soil-water retention surface

2010 ◽  
Vol 47 (6) ◽  
pp. 609-622 ◽  
Author(s):  
S. Salager ◽  
M. S. El Youssoufi ◽  
C. Saix
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Water Retention ◽  
Void Ratio ◽  
Silty Sand ◽  
Soil Water Retention ◽  
Initial Void Ratio ◽  
Hydromechanical Behaviour ◽  
Determination Methods

This paper deals with the definition and determination methods of the soil-water retention surface (SWRS), which is the tool used to present the hydromechanical behaviour of soils to highlight both the effect of suction on the change in water and total volumes and the effect of deformation with respect to the water retention capability. An experimental method is introduced to determine the SWRS and applied to a clayey silty sand. The determination of this surface is based on the measurement of void ratio, suction, and water content along the main drying paths. These paths are established for five different initial states. The experimental results allow us to define the parametric equations of the main drying paths, expressing both water content and void ratio as functions of suction and initial void ratio. A model of the SWRS for clayey silty sand is established in the space (void ratio – suction – water content). This surface covers all possible states of the soil inside the investigated range for the three variables. Finally, the SWRS is used to study the relations between water content and suction at a constant void ratio and between void ratio and suction at a constant water content.

A new procedure for the determination of soil-water retention curves by continuous drying using high-suction tensiometers

2011 ◽  
Vol 48 (2) ◽  
pp. 327-335 ◽  
Author(s):  
S. D.N. Lourenço ◽  
D. Gallipoli ◽  
D. G. Toll ◽  
C. E. Augarde ◽  
F. D. Evans
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Water Retention ◽  
Soil Water Retention ◽  
Mass Measurements ◽  
Discrete Measurement ◽  
Wetting Process ◽  
High Suction

Soil-water retention curves (SWRCs) can be determined using high-suction tensiometers (HSTs) following two different procedures that involve either continuous or discrete measurement of suction. In the former case, suction measurements are taken while the sample is permanently exposed to the atmosphere and the soil is continuously drying. In the latter case, the drying or wetting process is halted at different stages to ensure equalization within the sample before measuring suction. Continuous drying has the advantage of being faster; however, it has the disadvantage that the accuracy of mass measurements (necessary for the determination of water content) is affected by the weight and stiffness of the cable connecting the HST to the logger. To overcome this problem, an alternative continuous drying procedure is presented in this paper in which two separate but nominally identical samples are used to obtain a single SWRC; one sample is used for the mass measurements, while a second sample is used for suction measurements. It is demonstrated that the new continuous drying procedure gives SWRCs that are similar to those obtained by discrete drying.

scholarly journals Investigation into water retention behaviour of deformable soils

2013 ◽  
Vol 50 (2) ◽  
pp. 200-208 ◽  
Author(s):  
Simon Salager ◽  
Mathieu Nuth ◽  
Alessio Ferrari ◽  
Lyesse Laloui
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Water Retention ◽  
Void Ratio ◽  
Degree Of Saturation ◽  
Retention Data ◽  
Soil Water Retention ◽  
Retention Behaviour ◽  
Wide Range ◽  
Water Retention Behaviour

The paper presents an experimental and modelling approach for the soil-water retention behaviour of two deformable soils. The objective is to investigate the physical mechanisms that govern the soil-water retention properties and to propose a constitutive framework for the soil-water retention curve accounting for the initial state of compaction and deformability of soils. A granular soil and a clayey soil were subjected to drying over a wide range of suctions so that the residual state of saturation could be attained. Different initial densities were tested for each material. The soil-water retention curves (SWRCs) obtained are synthesized and compared in terms of water content, void ratio, and degree of saturation, and are expressed as a function of the total suction. The studies enable assessment of the effect of the past and present soil deformation on the shape of the curves. The void ratio exerts a clear influence on the air-entry value, revealing that the breakthrough of air into the pores of the soil is more arduous in denser states. In the plane of water content versus suction, the experimental results highlight the fact that from a certain value of suction, the retention curves corresponding to different densities of the same soil are convergent. The observed features of behaviour are conceptualized into a modelling framework expressing the evolution of the degree of saturation as a function of suction. The proposed retention model makes use of the theory of elastoplasticity and can thus be generalized into a hysteretic model applicable to drying–wetting cycles. The calibration of the model requires the experimental retention data for two initial void ratios. The prediction of tests for further ranges of void ratios proves to be accurate, which supports the adequacy of formulated concepts.

Isotropic yielding of unsaturated cemented silty sand

2013 ◽  
Vol 50 (8) ◽  
pp. 807-819 ◽  
Author(s):  
M. Arroyo ◽  
M.F. Amaral ◽  
E. Romero ◽  
A. Viana da Fonseca
Keyword(s):  
Water Content ◽  
Water Retention ◽  
Void Ratio ◽  
Dry Weight ◽  
Silty Sand ◽  
Initial Void Ratio ◽  
Naturally Occurring ◽  
Experimental Campaign ◽  
Hardening Mechanisms ◽  
Designed Materials

Unsaturated cemented soils are frequent both as designed materials and as naturally occurring layers. Both desiccation and cementation act separately as hardening mechanisms, but it is not clear how exactly their effects combine. Do they enhance one another? Are they mutually reinforcing? This study presents results from an experimental campaign aimed at answering these questions. Five different mixtures of soil (a granite saprolite) and cement (with cement contents in the range 0% to 7% on a dry weight basis) are tested in isotropic compression at four different water content levels. Initial void ratio is also controlled, using two initial compaction densities. Loading is performed at constant water content and suction is inferred from a set of water retention curves obtained from parallel psychrometric and pore-size distribution measurements. The range of yield stresses explored in this study covers almost two orders of magnitude and extends up to 7 MPa at suction values of up to 14 MPa. Both desiccation and cementation increase yield stress, but their effects are less marked when both act together, and therefore they are not mutually reinforcing.

Modelling effects of root growth and decay on soil water retention and permeability

2019 ◽  
Vol 56 (7) ◽  
pp. 1049-1055 ◽  
Author(s):  
J.J. Ni ◽  
A.K. Leung ◽  
C.W.W. Ng
Keyword(s):  
Root Growth ◽  
Soil Water ◽  
Water Retention ◽  
Void Ratio ◽  
Silty Sand ◽  
Coarse Grained ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Root Decay

Plant roots can change the soil water retention curve (SWRC) and saturated permeability (ksat) of vegetated soils. However, there is no model that could capture both the effects of root growth and root decay on these soil hydraulic properties simultaneously. This note proposes a new void ratio function that can model the decrease and increase in soil void ratio due to root occupancy (upon growth) and root shrinkage (upon decay), respectively, in an unsaturated vegetated coarse-grained soil. The function requires two root parameters; namely, root volume ratio and root decay ratio, both of which can be readily measured through root excavation and image-based analysis. The new function is incorporated into a void ratio–dependent SWRC model for predicting the SWRC of vegetated soils. Similarly, the same function can be combined with the Kozeny–Carman equation for predicting ksat. The model prediction is then compared with a set of new field test data and an existing laboratory dataset for a silty sand vegetated with plant species under the family Schefflera. Good agreements are obtained between the measurements and predictions.

scholarly journals Determination of the Soil Water Retention Curve Using the Flow Pump

2015 ◽  
Vol 68 (2) ◽  
pp. 207-213
Author(s):  
Luciana Portugal Menezes ◽  
Waldyr Lopes Oliveira Filho ◽  
Cláudio Henrique Carvalho Silva
Keyword(s):  
Soil Water ◽  
Water Retention ◽  
Unsaturated Flow ◽  
Silty Sand ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Retention Curve ◽  
Flow Problems ◽  
Flow Pump

AbstractReliable measurements of the Soil Water Retention Curve, SWRC, are necessary for solving unsaturated flow problems. In this sense, a method to obtain the SWRC of a silty sand using a flow pump, as well as details about procedures and some results, are herein presented. The overall conclusion is that the new method is very convenient, fully automated, and produces reliable results in a fast and easy way, making the technique very promising.

scholarly journals Evolution of the soil water retention curve based on plastic volumetric strain

2020 ◽  
Vol 195 ◽  
pp. 02016
Author(s):  
J. Kodikara ◽  
C. Jayasundara
Keyword(s):  
Soil Water ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Void Ratio ◽  
Volumetric Strain ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Retention Curve ◽  
Plastic Volumetric Strain

The water retention behaviour of soil can be defined as the relationship between the degree of saturation (or water content) and suction at a constant temperature, which characterises the hydraulic behaviour of unsaturated soils, normally represented as the soil water retention curve (SWRC). The SWRC is commonly measured at nominal net stress by initially saturating a soil specimen and then subjecting it to drying and wetting paths, resulting in major drying and wetting curves. However, there is evidence that during these major drying and wetting paths and initial saturation, soil can undergo volumetric deformation with changes in void ratio, sometimes plastically. Therefore, for coupling the SWRC with mechanical behaviour, the dependency of SWRC on other state variables such as void ratio has been proposed. In this paper, an approach to defining SWRC for a particular plastic volumetric strain is presented within the generalised MPK model. The SWRC evolves as soil is subjected to wet/dry cycles, eventually approaching drying and wetting curves relevant to an environmentally-stabilised state. The performance of this model is demonstrated by the simulation of the loading/unloading/drying/wetting paths followed in a laboratory experiment. In addition, the evolution of the commonly-considered major drying and wetting curves is simulated, highlighting key features of the environmentally-stabilised line..

Retrieving soil-water retention curve at the wet part by remote sensing

2020 ◽  
Author(s):  
Zampela Pittaki-Chrysodonta ◽  
Per Moldrup ◽  
Bo V. Iversen ◽  
Maria Knadel ◽  
Lis W. de Jonge
Keyword(s):  
Remote Sensing ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Spectral Data ◽  
Water Retention ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Retention Curve

<p>The soil water retention curve (SWRC) at the wet part is important for understanding and modeling the water flow and solute transport in the vadose zone. However, direct measurements of SWRC is often laborious and time consuming processes. The Campbell function is a simple method to fit the measured data. The parameters of the Campbell function have been recently proven that can be predicted using visible-near-infrared spectroscopy. However, predicting the SWRC using image spectral data could be an inexpensive and fast method. In this study, 100-cm<sup>3</sup> soil samples from Denmark were included and the soil water content was measured at a soil-water matric potential from pF 1 [log(10)= pF 1] up to pF 3. The anchored Campbell soil-water retention function was selected instead of the original. Specifically, in this function the equation is anchored at the soil-water content at pF 3 (θ<sub>pF3</sub>) instead at the saturated water content. The image spectral data were correlated with the Campbell parameters [θ<sub>pF3</sub>, and the pore size distribution index (Campbell b). The results showed the potential of remote sensing to be used as a fast and alternative method for predicting the SWRC in a large-scale.</p>

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