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 ...

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.

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.

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.

... 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.

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.

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.

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.

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.