Unsaturated soil

Considerably long periods of time are required to measure soil-water characteristic curves using conventional equipment such as pressure plate apparatus or a Tempe cell. A commercially available, small-scale medical centrifuge with a swinging type rotor assembly was used to measure the soil-water characteristic curves on statically compacted, fine-grained soil specimens. A specimen holder was specially designed to obtain multiple sets of water content versus suction data for measuring the soil-water characteristic curve at a single speed of rotation of the centrifuge. The soil-water characteristic curves were measured for three different types of fine-grained soils. The three soils used in the study were processed silt (liquid limit, wL = 24%; plasticity index, Ip = 0; and clay = 7%), Indian Head till (wL = 35.5%, Ip = 17%, and clay = 30%), and Regina clay (wL = 75.5%, Ip = 21%, and clay = 70%). The soil-water characteristic curves for the above soils were measured in 0.5, 1, and 2 ...

In this paper, lab tests coupled to a semi-pilot test section are used to derive data for the calibration of a numerical model. The paper is aimed at proposing a set of experiments, which can be used to calibrate a numerical model before using it on defined soils. The complexity of the phenomenon of transport of reactive pollutants in soil has to be faced in the most complete way. The different behaviour of soil after wet/dry cycles with respect to the fluidodynamic characteristics and the importance to consider the local biomass behaviour in case of organic contaminant has been underlined. An optimal approach has to take into account all the different components and here a simple series of experimental procedure is presented. The sensitivity analysis of the numerical model has shown that its results are not so much dependent on the classical numerical aspects (time or space increments) but mainly on a set of parameters related to soil structure which must then be derived through a good calibration. (P. Viotti). produced contamination of several aquifers all over the world. Contaminants dispersed at the land surface migrate through the vadose zone before being advected and dispersed by flowing groundwater. Solute transport in unsaturated soils has been the topic of experimental, theoretical research and studies above numerical simulation aspects . The behaviour and fate of chemicals in the vadose zone is complex , being a process occurring in conditions strongly influenced 0304-3800/$ -see front matter

Knowledge of soil hydraulic properties is required for soil-water flow models. Although many studies of individual methods exist, comparisons of methods are uncommon. Therefore, we compared application ranges and results for six laboratory methods for determining hydraulic conductivity or diffusivity on eolian sand, eolian silt loam, marine sandy loam, and fluviatile silt loam. The methods, hot air, sorptivity, crust, drip inflltrometer, Wind's evaporation, and one-step outflow, fall into three groups: (i) those that only yield a conductivity curve; (ii) those that yield a simultaneous estimate of conductivity, diffusivity, water content, and pressure head; and (iii) those that yield a diffusivity curve. Diffusivities were converted to conductivities with a water retention curve. One main difference between the methods was the pressure head-water content range. Despite the large differences between the methods, the results for the first two groups tended to be similar. The results of the third group did not match well with those of the first two. It proved difficult to compare these methods correctly due to hysteresis.

The authors should be commended for presenting such an innovative approach to the estimation of the collapse potential in unsaturated soils. This is a pioneering work that sets the basis for further developments on the use of pressuremeter tests for the mechanical characterization of unsaturated soils in the framework of advanced constitutive models. This area has not been adequately investigated to date, mainly due to the lack of a methodology for pressuremeter tests in unsaturated soils and the complexity of constitutive models. The present discussion intends to offer the opportunity for a debate with the authors on some

This paper presents a complete finite-element treatment for unsaturated soil problems. A new formulation of general constitutive equations for unsaturated soils is first presented. In the incremental stress-strain equations, the suction or the pore water pressure is treated as a strain variable instead of a stress variable. The global governing equations are derived in terms of displacement and pore water pressure. The discretized governing equations are then solved using an adaptive time-stepping scheme which automatically adjusts the time-step size so that the integration error in the displacements and pore pressures lies close to a specified tolerance. The non-linearity caused by suction-dependent plastic yielding, suction-dependent degree of saturation , and saturation-dependent permeability is treated in a similar way to the elastoplasticity. An explicit stress integration scheme is used to solve the constitutive stress-strain equations at the Gauss point level. The elastoplastic stiffness matrix in the Euler solution is evaluated using the suction as well as the stresses and hardening parameters at the start of the subincrement, while the elastoplastic matrix in the modified Euler solution is evaluated using the suction at the end of the subincrement. In addition, when applying subincrementation, the same rate is applied to all strain components including the suction.

Leaking underground storage tanks are a worldwide problem nowadays, therefore gasoline degradation
and distribution in the subsurface have been widely studied. Brazil is the only country to currently use
ethanol as fuel and as an oxygenate additive to gasoline, in amounts varying from 20 to 26% v/v.
Consequently, both gasoline and ethanol may contaminate the environment when spills and leaks occur.
Some authors suggest that despite the high degradability of gasoline, its degradation in the aquifer is
hindered by the preferential biodegradation of ethanol, which would delay gasoline degradation;
however, processes in the unsaturated zone are far less understood. The present study concentrates on
degradation and distribution processes of ethanol-amended gasoline in tropical soil under unsaturated
conditions. A multi-parametrical approach was adopted to assess the effects of ethanol on the fate of
gasoline. Undisturbed natural soil was used to evaluate biodegradation processes while tank experiments
determined differences in infiltration, distribution and retention of gasoline in unsaturated artificial
porous medium. Physical, chemical and microbiological results suggest that ethanol enhances BTEX
retention in soil, boosts microbial activity but delays BTEX biodegradation.

At present, the road construction along hilly terrains in many parts of Thailand, increase rapidly due to urban expansion. The construction techniques mostly used involve cut and fill and the construction materials found in the area. Preliminary field survey found that argillaceous rock prevail in the study area of Mar Hong Son Province. This material tends to deteriorate with time, and decay to plasticity soils. It is the shink-swell behavior and loss of shear strength due to wetting that normally cause problem, with this material. This is consistent with the collapse of the hillside road, especially during the rainy season. This paper focuses on study of the mechanical behavior of the compacted decomposed rock in unsaturated condition. This study also involves field

The Intergovernmental Panel on Climate Change (IPCC) provides convincing evidence of global warming as a result of increased greenhouse gas production. There has been a greater occurrence of extreme climate events in recent decades. We need to ensure that our buildings and infrastructure can cope with such events and possibly more extreme events in the future. A good grounding in unsaturated soil mechanics will be necessary to understand future changes involving the drying and desiccation of soils that will occur in dry seasons and the wetting and infiltration processes that prevail during wet seasons. To predict the impacts of climate change will require the use of robust numerical modelling of climate/soil interactions that can be used to model the effects of future climate regimes. To achieve this we need high quality field observations involving climate/soil interaction that can be used to validate the models. This paper reports on a study in the UK to acquire such data.

Existing models for predicting the small strain behaviour of unsaturated soil are not capable of predicting the initial shear stiffness during suction reduction under normally consolidated conditions. This problem has been addressed in the present study by combining an existing elastoplastic model and recent experimental data to provide a new model for the initial shear stiffness. The model, which is similar to that typically adopted for saturated soils, uses the average skeleton stress and an additional function of the degree of saturation. This new model not only captures the behaviour of the new experimental results, but it also describes a unique relationship between saturated and unsaturated soils.

Physicochemical analyses were carried out on soil samples from four different waste dumpsites in the Federal University of Technology Akure (FUTA), Nigeria to ascertain the effects of the refuse dumpsites on soil and groundwater qualities. Dumpsite locations are Physics Laboratory (PHY), Post Graduate Hostel (PG), School of Earth and Mineral Science (SEMS) and Staff Quarters (STQ). Soil samples collected at distances 0 (dumpsite), 10 and 20 m intervals away from the dumpsite were analyzed and at depths 10, 20 and 30 cm. Parameters determined include pH, Electrical Conductivity (EC), Magnesium (Mg), Calcium (Ca), Sodium (Na), Phosphorus (P), Nitrogen (N), Potassium (K), Organic Carbon (OC), Organic Matter (OM) and heavy metals such as Copper (Cu) and Lead (Pb) and subjected to relevant statistical analysis. Most of the parameters analyzed indicated pollution and were below the Food and Agricultural Organization (FAO) limits. P and Mg concentrations ranged from 1.19 to 1.25mg/kg and 3.17 to 13.61mg/kg respectively which indicated pollution. Out of heavy metals analyzed, Cu was 1.75mg/kg and Pb was not detected. Statistical analysis indicated signicant differences at 95% level. The result showed that the soil samples were mildly polluted and therefore not suitable for crop production.

The unsaturated soil hydraulic functions involving the soil-water retention curve (SWRC) and the hydraulic conductivity provide useful integrated indices of soil quality. Existing and newly devised methods were used to formulate pedotransfer functions (PTFs) that predict the SWRC from readily available soil data. The PTFs were calibrated using a large soils database from Hungary. The database contains measured soil-water retention data, the dry bulk density, sand, silt and clay percentages, and the organic matter content of 305 soil layers from some 80 soil profiles. A three-parameter van Genuchten type function was fitted to the measured retention data to obtain SWRC parameters for each soil sample in the database. Using a quasi-random procedure, the database was divided into ''evaluation'' (EVAL) and ''test'' (TEST) parts containing 225 and 80 soil samples, respectively. Linear PTFs for the SWRC parameters were calculated for the EVAL database. The PTFs used for this purpose particle-size percentages, dry bulk density, organic matter content, and the sand/silt ratio, as well as simple transforms (such as logarithms and products) of these independent variables. Of the various independent variables, the eight most significant were used to calculate the different PTFs. A nonlinear (NL) predictive method was obtained by substituting the linear PTFs directly into the SWRC equation, and subsequently adjusting the PTF parameters to all retention data of the EVAL database. The estimation error (SSQ) and efficiency (EE) were used to compare the effectiveness of the linear and nonlinearly adjusted PTFs. We found that EE of the EVAL and the TEST databases increased by 4 and 7%, respectively, using the second nonlinear optimization approach.

By means of a drainage and seepage tank, an experimental flow net system inside the body of a homogeneous earth embankment dam model, formed from Leighton Buzzard Silica sand, was developed and studied in this experimental research paper. Water flow through dams is one of the basic problems for geotechnical engineers. Seepage analysis in an important factor to be considered in the proper design of many civil engineering structures. Seepage can occur in both through the structure itself as the case of earth dams and under foundations of an engineering structure. Successful seepage analysis is achieved on the proper and accurate construction of a flow net. Amongst the various existing methods of seepage analysis, the "Finite Element Method" and the method of "Experimental Flow Nets" are the most widely used ones. Construction of a flow net is mainly used for solving water flow problems through porous media where the geometry makes sometimes analytical solutions impractical. This method is usually used in soil mechanics, geotechnical or civil engineering as an initial check for problems of water flow under hydraulic structures like embankments or dams. As such, a grid obtained by drawing a series of equipotential lines and stream or flow lines is called a flow net. In this procedure the Laplace equation principles must be satisfied. Hence, the construction of a flow net is an important tool in analysing two-dimensional irrotational flow problems and provides an approximate solution to the flow problem by following simple rules, as initially set out by Forchheimer, 1900, and later refined by Casagrande,1937. It can also be very useful tool even for problems with complex geometries, as proven in this experimental research paper. The objectives of this experimental research paper are: • To determine the position and shape of the flow line representing the uppermost free water surface inside the body of a dam by using a drainage and seepage tank, • To conceptualise the flow lines system and to demonstrate that each flow line starts perpendicular to the upstream slope of the dam and that that slope is a boundary equipotential line, • To construct an experimental flow net and subsequently to verify and analyse it by the FEA method, • To calculate the rate of seepage through the dam body, and • To summarise the calculations and experimental findings in a concise and readable format.

The unsaturated soil behavior is of prime importance in many of the geotechnical and geoenvironmental applications. The characterization of the engineering behavior of unsaturated soil is entirely dependent on the soil-water characteristic curve (SWCC), which is a graphical relationship between water content (either gravimetric or volumetric) or degree of saturation and soil suction. For decades, experimental studies are performed to investigate the relationship between the soil suction and volumetric water content (SWCC). Most of the reported studies, discuss about drying SWCC due to the simplicity of its measurement. It must be noted that wetting SWCC is equally important for situations like seepage through unsaturated soil. With this in view, effort has been made in this paper to critically review the recent research outcomes in the measurement of wetting SWCC. The advantages and limitations associated with different measurement procedures are presented. This paper also describes a new approach for developing wetting SWCC with the help of a column test set up. The methodology has been demonstrated by determining the wetting SWCC of a locally available sandy soil.

The determination of soil-water characteristic curve (SWCC) is of major concern in unsaturated soil mechanics. For decades experimental and theoretical studies are performed to investigate the constitutive relationship between soil suction and volumetric water content. The major objective of our study is to generate an extensive experimental database for sand with a relevant suction range of just a few kPa. This database enables to derive conclusions on the sensitivity of hydraulic properties regarding different experimental procedures. Further, one objective is the comparison of results for SWCC derived from steady state and transient state tests. While the first type of tests considers equilibrium states, the subsequent test is related to non-equilibrium states. Experimental results are generated from a so called homogenous element test (modified pressure plate apparatus) and an initial boundary value experiment (column testing device) considering different hydraulic loading path directions. The experiments are analysed for sand with different initial states. Finally results are presented for SWCC including initial curves, main curves, and scanning paths. Discussion is focused on transient state versus steady state flow tests. No significant dynamic effects are observed for the sand studied. Results of well controlled element tests compare very well to initial boundary value experiments implying higher experimental efforts.

... Lourenco, SDN, Gallipoli, D. , Toll, DG, and Evans, F. (2006) Use of Tensiometers for the Measurement of Soil Suction. In: 10th Confresso Nacional de Geotecnia, 22 - 26 May 2006, Lisboa, Portugal. ... Authors: Lourenco, SDN, Gallipoli, D. , Toll, DG, and Evans, F. ...

THIS IS NATURE SIGNALING THE END OF DUALITY 
THIS IS HUGE - CHANGE THE ENTIRETY OF CREATION - NO DUALITY ANYWHERE.
IT IS VERY CLEARLY A PREDETERMINED ADVANCEMENT OF HUMAN CONSCIOUSNESS - THIS BUBBLE IS TOO WELL DESIGNED - EUPHORIA CANCELS KARMA

Au cours des dernières décennies, un intérêt croissant est porté à la terre crue en tant qu'éco matériau de construction pour son caractère local, sa capacité à réguler l'hygrométrie des espaces intérieurs et la faible consommation d'énergie qui caractérise son cycle de vie global. Cependant, le développement de la construction en terre crue compactée est limitée par certains freins comme une faible résistance mécanique ou encore une sensibilité à l'infiltration de l'eau. Le principal but de cette étude est d'améliorer les propriétés mécaniques de briques de terre crue par l'emploi d'une nouvelle procédure de compactage : si la pratique commune est d'appliquer des charges de compactage relativement faibles (environ 15 MPa) durant quelques secondes, la méthode ici proposée se caractérise par l'application de pressions de compactage élevées (jusqu'à 100 MPa) pour une durée correspondant à la dissipation de la surpression de l'eau interstitielle. Pour cela, l'équipement mis au point est muni d'un système de drainage de l'eau interstitielle. Dans le cadre de cette étude, trois niveaux de contrainte de compactage ont été testés : 25, 50 et 100 MPa. Après compactage, les échantillons (une dizaine pour chaque niveau de contrainte) ont été placés dans une enceinte climatique (température de 25°C et humidité relative de 62 %) jusqu'à équilibre hydrique. Une fois cet équilibre atteint, les échantillons ont été testés en compression simple non confinés afin d'évaluer leur module d'Young et leur résistance mécanique en compression. Afin d'analyser et d'appréhender comment l'augmentation de la contrainte de compactage modifie le réseau poreux et la distribution de la taille des pores dans le matériau, des essais par porosimétrie d'intrusion au mercure ont été effectués sur des éprouvettes compactées respectivement à 25 et à 100 MPa. Cette nouvelle méthode de compactage à haute pression permettant l'atteinte de performances mécaniques élevées pourrait contribuer à la fois à changer les pratiques courantes de production de briques en terre crue comprimée, mais aussi orienter différemment la conception des presses. Ainsi, par l'atteinte de meilleurs performances mécaniques, un des principaux freins à l'utilisation de la terre crue comme matériau de construction serait levé.

The water movements in the unsaturated zone, together with the water holding capacity of this zone, are very important for the water demand of the vegetation, as well as for the recharge of the groundwater storage. A fair description of the flow in the unsaturated zone is crucial for predictions of the movement of pollutants into groundwater aquifers. This article presents an overview of the modelling process for water flow in the unsaturated zone, input data requirements, boundary conditions and related software packages.

An unsaturated soil is a state of the soils. All soils can be partially saturated with water. Therefore, constitutive models for soils should ideally represent the soil behaviours over entire ranges of possible pore pressure and stress values and allow arbitrary stress and hydraulic paths within these ranges. The last two decades or so have seen significant advances in modelling behaviours of unsaturated soils. A review of constitutive models for unsaturated soils is presented. In particular, it focuses on the fundamental principles that govern the volume change, shear strength, yield stress, water retention and hydro-mechanical coupling. Alternative forms of these principles are critically examined in terms of their predictive capacities for experimental data, the consistency between these principles and the continuity between saturated and unsaturated states.

A qualitative study of fabrics as observed through a petrological microscope was carried out. Some evidence is shown of differences in the fabrics of the samples, resulting from differences in compacted properties and subsequent loading/wetting. These differences in fabrics are also discussed in relation to the observations and hypotheses made about the soil-water retention and collapse behaviours, described in Chapters 4 and 5.

The progress in constitutive models for unsaturated soils is briefly reviewed at first; and then the state of the art of elastoplastic constitutive models for unsaturated soils is summarized. This paper focuses on introducing an elastoplastic model coupling hydraulic and mechanical behaviour of unsaturated non-expansive soils. As an example, a coupled elastoplastic constitutive model proposed recently by the author et al. and its model predictions are shown herein for illustrating the structure of the coupled model and its performance. Hydraulic hysteresis in the soil-water characteristic is modeled as an elastoplastic process with the elastic region of the saturation degree. The effect of change in degree of saturation on the stress-strain-strength behaviour and the effect of change in void ratio on the soil-water characteristics are taken into consideration in the model; in addition to the effect of suction on the hydraulic and mechanical behaviour. By using the same values of the model parameters, hydraulic and mechanical behaviour of unsaturated soils can be consistently predicted under the control of suction or water content along various total stress paths. The elastoplastic constitutive model for unsaturated expansive soils and the application of the coupled model to the finite element computations are introduced in brief.

This paper presents an overview of constitutive modelling of unsaturated soils and the numerical algorithms for solving the associated boundary value problems. It first discusses alternative stress and strain variables that can be used in constitutive models for unsaturated soils. The paper then discusses the key issues in unsaturated soil modelling and how these issues can be incorporated into an existing model for saturated soils. These key issues include (1) volumetric behaviour associated with saturation or suction changes; (2) strength behaviour associated with saturation and suction changes, and (3) hydraulic behaviour associated with saturation or suction changes. The paper also shows how hysteresis in soil-water characteristics can be incorporated into the elasto-plastic framework, leading to coupled hydro-mechanical models. Finally, the paper demonstrates the derivation of the incremental stress-strain relations for unsaturated soils and discusses briefly the new challenges in implementing these relations into the finite element method.

Plate-load tests are a common field method to estimate soil bearing pressure. Classic-result-test interpretations do not consider the matric suction effect. This paper analyzes the matric suction effect in bearing pressure from plate-load tests conducted in a lean clay soil. Seven plate-load tests were carried on in an unsaturated lean clay deposit; two of them were performed in saturated condition to verify the site homogeneity and test repeatability, five of them took into account different matric-suction values. Matric suction along the plate influence zone was monitored with four Jet Fill tensiometers, inserted at 0.1, 0.3, 0.6 and 0.9 m around every test pit. The results show bearing pressure values are highly influenced by matric suction changes.

A simple thermo-hydro-mechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way.

The soils of Jinka in Southern Ethiopia were studied based on the detail works on soil pit description, characterizing and classification following the FAO and USDA guidelines. For this, along with the topo-sequence and landscape, six soil profiles were opened on an area of 100 ha of research field to make them suit for sustainable soil management practices. The soils were generally described as dark reddish brown to very dark brown and deep. These soils were characterized as slightly (4.87) to moderately acidic (6.18). The OC and available phosphorus were found to range from low to medium. All micronutrients were found to be highly associated with lower soil reaction. These soils group can be classified as Cambisols. Therefore, amending the soil with lime based on exchangeable acidity, essential and deficient nutrients will be vital for supplying food and feed crops in the region. However, continuous assessment of the nutrient status at every five to seven years is necessary to make sure that the soil quality is maintained.

The van Genuchten (vG) function is often used to describe the soil water retention curve (SWRC) of unsaturated soils and fractured rock. The objective of this study was to develop a method to determine the vG model parameter m from the fractal dimension. We compared two approaches previously proposed by van Genuchten and Lenhard et al. for estimating m from the pore size distribution index of the Brooks and Corey (BC) model. In both approaches we used a relationship between the pore size distribution index of the BC model and the fractal dimension of the SWRC. A dataset containing 75 samples from the UNSODA unsaturated soil hydraulic database was used to evaluate the two approaches. The statistical parameters showed that the approach by Lenhard et al. provided better estimates of the parameter m. Another dataset containing 72 samples from the literature was used to validate Lenhard's approach in which the SWRC fractal dimension was estimated from the clay content. The estimated SWRC of the second dataset was compared with those obtained with the Rosetta model using sand, silt, and clay contents. Root mean square error values of the proposed fractal approach and Rosetta were 0.081 and 0.136, respectively, indicating that the proposed fractal approach performed better than the Rosetta model.

Composite geotextiles with polyester yarn reinforcement have been commonly used in combination with unsaturated soils. Both unsaturated and saturated shear strength of the interfaces were investigated between a composite geotextile and three major types of materials: silty sand (SM), low-plasticity silt (ML) and highplasticity clay (CH) in a direct shear box. The interfaces were formed using two methods (A and B) to reflect the wide range of possible contact conditions in practice. Method A involved statically compacting the soil directly on top of the composite geotextile, while for Method B, the soil was statically compacted in a separate mold and later brought into contact with the composite geotextile. Type B interfaces required a larger displacement to mobilize the shear strength than Type A interfaces. The ultimate failure envelopes of SM and ML soils were similar to those oftheir interfaceshearing. Notably, the failureenvelopes for the clay-geotextile interfaceof both types were higher than that of clay alone. The unsaturated soil-only shearing had a higher peak strength and tended to dilate more than saturated soil-only shearing, while unsaturated soil-interface shearing appeared to be more contractant than saturated interface shearing. The strength variations with suction for all tested soils and interface shearing were clearly non-linear. A new model that takes account of the condition of soil-geotextile contact intimacy is proposed for predicting the variation of interface strength with suction, based on the variation of the soil's apparent cohesion with suction and the geotextile-water retention curve.

“Raw earth” (“terre crue” in French) is an ancient building material consisting of a mixture of moist clay and sand which is compacted to a more or less high density depending on the chosen building technique. A raw earth structure could in fact be described as a “soil fill in the shape of a building”. Despite the very nature of this material, which makes it particularly suitable to a geotechnical analysis, raw earth construction has so far been the almost exclusive domain of structural engineers and still remains a niche market in current building practice. A multitude of manufacturing techniques have already been developed over the centuries but, recently, this construction method has attracted fresh interest due to its eco-friendly characteristics and the potential savings of embodied, operational and end-of-life energy that it can offer during the life cycle of a structure. This paper starts by introducing the advantages of raw earth over other conventional building materials followed by a description of modern earthen construction techniques. The largest part of the manuscript is devoted to the presentation of recent studies about the hydro-mechanical properties of earthen materials and their dependency on suction, water content, particle size distribution and relative humidity.

The paper gives a brief description of double wall cell triaxial equipment for testing soil samples under unsaturated conditions and presents results of some of the calibrations necessary to achieve accurate measurements of inner cell water volume, pore water volume, pressure, load and displacement. The calibration of the measurement devices showed linear relationships between the raw readings and applied values with the regression constants differ from 1 and 0. The result of apparent volume change calibrations showed significant correlation between cell water volume fluctuation and temperature fluctuation inside testing room. A correction to the measured volume was therefore required to reduce the effects of long-term temperature fluctuation on the measured volume. Investigation of the accuracy of volume change measurement with the double wall cell showed excellent matching between the inner cell volume change and pore water volume change under saturated conditions, indicating the high reliability of the double wall system for apparent volume change measurements.

Determinations of unsaturated soil parameters using experimental procedures are time consuming and difficult. In recent years, the soil–water characteristic curve (SWCC) has become an important tool in the interpretation of the engineering behavior of unsaturated soils. Difficulties associated with determining such parameters have justified the use of indirect determination. This paper presents the general nature of the SWCC for soils with different plasticity limits, index and gradation, in terms of gravimetric water content and degree of saturation versus soil matric suction from Anbar governorate. In order to investigate possible relationships between the plasticity limits , index, percent passing no.200a and SWCC, 7 type of soils were tested to find its SWCC experimentally and compared the result with the curves obtained from different model presented in the literature. The objectives of the paper were to check the validity of these models with the experimental results. The results shows a good agreement and to present a simple method for inferring the SWCC for soils, taking into account the liquid limit, plastic limit, plasticity index and percent of fines passing sieve no.200.

Au cours des dernières décennies, un intérêt croissant est porté à la terre crue en tant qu'éco-matériau de construction pour son caractère local et la faible consommation d’énergie qui caractérise son cycle de vie global. Toutefois, sa résistance mécanique relativement faible et sa sensibilité à l'eau freinent le développement de ce matériau. Le principal but de cette étude est d’améliorer les propriétés mécaniques de briques de terre crue par l’emploi d’une nouvelle procédure de compactage à pression élevée maintenue pendant une durée correspondante au temps de consolidation. Un système de compactage a été élaboré afin de compacter le sol à haute pression en permettant le drainage de l’eau interstitielle. Dans un premier temps, les caractéristiques géotechniques du matériau d'étude ont été déterminées. Après compactage à 25, 50 et 100 MPa, les échantillons ont été placés dans une enceinte climatique (25°C, humidité relative de 62 %) jusqu’à équilibre hydrique, puis testés afin d’évaluer leur module d’Young et leur résistance mécanique en compression. Cette nouvelle méthode de compactage à haute pression a permis d'atteindre des performances mécaniques élevées. Ainsi, un des principaux freins à l'utilisation de la terre crue comme matériau de construction serait levé.

The current research has investigated the soil quality status under dryland vegetation of Yabello district, Southern Ethiopia in which we should identify the nature and extent of salinity problem of the area for further research bases. About 48 soil samples were taken from 0-30, 31-60, 61-90 and 91-120 cm soil depths by opening 12 representative soil profile pits at 1.5 m depth. Soil color, texture, bulk density, Soil Organic Carbon (SOC), Cation Exchange Capacity (CEC), Na, K, Mg, Ca, CaCO3, gypsum (CaSO4), pH, Sodium Adsorption Ratio (SAR), Exchangeable Sodium Percentage (ESP) were analyzed. The dominant soil texture was silty-clay-loam. Bulk density varied from 1.1 to 1.31 g/cm 3. High SOC content was observed in 0-30 cm. The soil pH ranged from 7.1 to 8.6. The electrical conductivity shows indirect relationship with soil depth while CaCO3 and CaSO4 concentrations were observed in a direct relationship with depth. About 41% are non-saline, 38.31% saline, 15.23% saline-sodic and 5.46% sodic soils. Na concentration in saline soils was greater than Ca and Mg in all the soil depths. Ca and Mg contents were higher above 60 cm soil depth in non-saline soils. The concentrations of SO2-4 and HCO-3 were observed to be higher at the most lower depth than upper. SAR value tends to be higher at lower depths in saline and saline-sodic soils, but decreases at lower depth of the non-saline soils. The distribution of ESP above 60 cm depth was in an increasing order in saline and saline-sodic soils. The result of the research has shown the direction to which extent of salinity we should consider for the Commiphora plant species we want to grow on the area.

The prediction of heave in unsaturated, expansive soils has historically been studied primarily as a onedimensional type analysis. This paper proposes a methodology that can be used for the prediction of one-, two-, or three-dimensional heave. It is suggested that negative pore-water pressures (i.e., soil suctions) can be estimated through a saturated-unsaturated seepage analysis. The results of the seepage analysis are then used as input for the prediction of displacements in a stress-deformation analysis. The formulation of the governing partial differential equations for both seepage and stress-deformation is based on the general theory of unsaturated soils using two independent stress state variables. The elasticity parameter functions required for a stress-deformation analysis can be calculated from various tests, including conventional one-dimensional oedometer tests. The proposed method is studied and tested against data collected on a case history involving a slab-on-ground floor on Regina clay. The predicted results from the twodimensional analysis agree well with the measured data in terms of both total vertical displacements and final water contents in the soil. The results of a parametric study are also presented to show the effect of measured soil parameters (i.e., swelling index and initial void ratio) and assumed parameters (i.e., Poisson's ratio and coefficient of earth pressure at rest) on the predicted displacements.

Cracks along asphaltic-concrete shoulder of highways are one of the most common infrastructure damages found in the central part of Thailand where sedimentary soils of high plasticity were widely deposited and sometimes used as subgrade materials. This paper reports on a case study of highway route no. 357 in Supanburi province with emphasis on the mechanism of the longitudinal cracks initiated by desiccation cracking of the clay subgrade, as well as infiltration-induced slope instability. The studies included field investigation, monitoring of pore water pressure and suction, soil-water characteristic curve determination, as well as the suction monitored-direct shear tests. Seepage and deformation analyses were used to demonstrate the initiation of crack induced by evaporation from the embankment. Limit Equilibrium method was then used to analyse the influence of water-filled crack on the stability of the embankment.

Mounding often occurs beneath engineering structures designed to infiltrate reuse water. AQTESOLV software and a spreadsheet solution for Hantush, together with soil moisture water balance (SWAGMAN farm model), were used for quantitatively predicting the height and extent of groundwater mounding underground to assess the groundwater-flow simulations of infiltration from a hypothetical irrigation site. Horizontal and vertical permeability, aquifer thickness, specific yield, and basin geometry are among the aquifer and recharge properties inputs. For 2.2 ha sites, the maximum heights of the simulated groundwater mound ranges up to 0.29 m. The maximum areal extent of groundwater mounding measured from the edge of the infiltration basins of 0.24 m ranges from 0 to 75 m. Additionally, the simulated height and extent of the groundwater mounding associated with a hypothetical irrigation infiltration basin for 2.2 ha development may be applicable to sites of different sizes, using the recharge rate estimated from the SWAGMAN farm model. For example, for a 2.2 ha site with a 0.0002 m/day recharge rate, the irrigation infiltration basin design capacity (and associated groundwater mound) would be the same as for a 1.1 ha site with a 0.0004 m/day recharge rate if the physical characteristics of the aquifer are unchanged. The study claimed that the present modelling approach overcomes the complications of solving the Hantush equation for transient flow. The approach utilised in this study can be applied for other purposes such as measuring the feasibility of infiltrating water, attenuation zone, risk mitigation essential for decision-makers and planning regulators in terms of environmental effects and water use efficiency.

1] The simulation of conservative solute transport in a heterogeneous unsaturated soil depends on the description of spatial variability of soil hydraulic and chemical properties. The data from the Las Cruces Trench Site were used to explore the impact of alternative ways of describing the variability of hydraulic properties. Three different approaches were considered: Miller and Miller scaling, Leverett scaling, and a multistep approach involving categorization of water retention curves. Conditional sequential geostatistical simulation was used to generate equally probable realizations of soil properties for each approach, and these realizations were then used as input to a numerical simulator to quantify the resultant uncertainty in solute transport predictions. Simulation results show that the scaling techniques seem to oversimplify the description of heterogeneity in the Las Cruces Trench, leading to very narrow spaces of uncertainty. Because the multistep approach allows the reproduction of existing patterns of continuity of soil classes and of contrasting values of hydraulic properties in the field, it led to solute plumes that split into several preferential pathways that were not observed in the simulations based on the scaling approaches, which increased the standard deviation of the solute plume's moments. The results indicate that measurements of both water retention curves and saturated hydraulic conductivity need to be collected for more realistic, conservative studies of flow in heterogeneous unsaturated soils.

The water retention behaviour of soils is an essential aspect of understanding the unsaturated behaviour of soil materials. This paper looks at a relatively new method of measurement for soil water reten-tion curves, using high capacity tensiometers. New equipment for carrying out continuous measurements of water content, suction and volume change is described. The results are compared with traditional pressure plate measurements, as well as filter paper and chilled mirror hygrometer tests. It has been suggested that ten-siometer measurements and pressure plate data give different results. This is confirmed by the larger data set provided here. It is found that the differences between the techniques can be explained by different volumetric responses.

Theoretical procedures are presented in this paper to interpret the undrained shear strength of unsaturated soils in terms of two stress state variables, net normal stress, (σ - ua) and matric suction, (ua - uw). The proposed theory is tested on a glacial till representing optimum water content conditions both in confined and unconfined loading conditions. The studies presented in

The importance of unsaturated soil mechanics stems from the fact that the majority of geotechnical engineering projects are taking place in unsaturated soil zones. Soil suction, especially matric suction, is controlling the unsaturated soil behavior. However, measurements and determination of the soil suction is still a concern for geotechnical engineers and researchers regarding its accuracy, practicality, cost, and reliability. In this study, the filter paper method (FPM) has been adopted as a secondary indirect measurement of the suction. Both total and matric suction were measured for three different mixtures of coarse soil (sand) and fine soil (industrial Bentonite/Montmorillonite) at two different saturation levels for each mixture. An extensive characterization has been conducted for the soil samples and, thereafter, samples were prepared at 95% of the maximum dry density (MDD) on wet and dry sides of optimum for suction measurements. The soil-water-characteristic/retention curve (SWCC/SWRC) was then completed for each sample using an estimation method reported in the literature. A new prediction model has been developed, in this study to determine a fitting parameter for estimating SWCC. Also, a review on the application of SWCC to design of shallow foundations has been presented in a simplified manner. Finally, recommendations for future work and conclusions were reported.