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Methods of computation for soil heave based on an 'equivalent' net normal stress path approach often have built-in assumptions regarding the relationship between in situ matric suction, overburden stress, and swell pressure. The term 'matric suction equivalent' has been previously defined as the difference between in situ state of stress projected on the net normal stress plane (represented by swell pressure) and overburden stress. Correlations between matric suction, overburden stress, and swell pressure for matric suction values in excess of the air-entry value have not been well studied and are explored here for expansive soils. Filter paper (in-contact) and constant volume swell pressure tests were performed on undisturbed tube samples of expansive soils taken from Arizona, Colorado, and Texas. In general, the ratio of the matric suction equivalent to the matric suction decreases with increasing soil suction. An empirical relationship was established in which the matric suction equivalent was found to be proportional to the logarithm of the matric suction for in situ matric suctions greater than a certain value, termed as the 'intercept matric suction'. A correlation between the intercept matric suction and the soil's plasticity index (PI) was found for the clays of this study. The developed correlations represent a method for obtaining approximate estimates of in situ matric suction for expansive soils from PI and swell pressure data. Implications of the study findings for the use of an equivalent net normal stress approach for estimation of soil heave are explored. Key words: expansive soils, unsaturated soils, matric suction, matric suction equivalent, swell pressure, degree of saturation, heave prediction. Les methodes de calculs de soulevement de sol basees sur une approche avec contrainte normale nette << equivalente >> comportent souvent des hypotheses sur le lien entre la succion matricielle in situ, la pression lithostatique et la pression de gonflement. Le terme<>a ete precedemment defini comme la difference entre l'etat de contrainte in situ projete sur le plan de la contrainte normale nette (representee par la pression de gonflement) et la pression lithostatique. Les liens entre la succion matricielle, la pression lithostatique et la pression de gonflement pour les valeurs de succion matricielle depassant la charge capillaire critique n'ont pas encore ete formellement etudies et sont examines ici dans le cas des sols expansifs. Des essais de pression de gonflement sur papier filtre (en contact avec les echantillons) et a volume constant ont ete realises sur des tubes d'echantillons non perturbes de sols expansifs preleves en Arizona, au Colorado et au Texas. De fa^on generale, le quotient de l'equivalent succion matricielle par la succion matricielle diminue lorsque la succion du sol augmente. Une relation empirique a montre que l'equivalent succion matricielle semblait etre proportionnel au logarithme de la succion matricielle dans le cas ou cette derniere etait superieure a une certaine valeur qualifiee de << succion matricielle au point d'intersection >>. Une correlation entre la succion matricielle au point d'intersection et l'indice de plasticite (IP) du sol a ete decouverte dans le cas des argiles etudiees ici. Les correlations ainsi mises en evidence constituent une methode permettant d'obtenir des estimations approximatives de la succion matricielle in situ dans le cas des sols expansifs a partir des valeurs de l'IP et de la pression de gonflement. On evoque enfin les repercussions des decouvertes realisees dans la presente etude sur l'utilisation d'approches avec contrainte normale nette equivalente pour estimer le soulevement des sols. [Traduit par la Redaction] Mots-cles: sols expansifs, sols non satures, succion matricielle, equivalent succion matricielle, pression de gonflement, degre de saturation, prediction du soulevement., Introduction The vertical swelling of an expansive soil layer is generally referred to as heave. Existing methods for computing heave in response to soil wetting typically follow either an actual [...]

A slope stability model is derived for an infinite slope subjected to unsaturated infiltration flow above a phreatic surface. Closed form steady state solutions are derived for the matric suction and degree of saturation profiles. Soil unit weight, consistent with the degree of saturation profile, is also directly calculated and introduced into the analyzes, resulting in closed-form solutions for typical soil parameters and an infinite series solution for arbitrary soil parameters. The solutions are coupled with the infinite slope stability equations to establish a fully realized safety factor function. In general, consideration of soil suction results in higher factor of safety. The increase in shear strength due to the inclusion of soil suction is analogous to making an addition to the cohesion, which, of course, increases the factor of safety against sliding. However, for cohesive soils, the results show lower safety factors for slip surfaces approaching the phreatic surface compared to those produced by common safety factor calculations. The lower factor of safety is due to the increased soil unit weight considered in the matric suction model but not usually accounted for in practice wherein the soil is treated as dry above the phreatic surface. The developed model is verified with a published case study, correctly predicting stability under dry conditions and correctly predicting failure for a particular storm. DOI: 10.1061/(ASCE)GT.1943-5606.0000301 CE Database subject headings: Cohesive soils; Embankments; Failures; Landslides; Limit equilibrium; Pore pressure; Pore water; Slope stability; Soil suction; Unsaturated flow; Unsaturated soils. Author keywords: Cohesive soils; Embankment stability; Equilibrium; Failures; Landslides; Limit equilibrium; Pore pressure; Pore water; Pore-water pressure; Slope stability; Slopes; Soil suction; Stability; Suction; Unsaturated flow; Unsaturated soils.

The implementation of unsaturated soil mechanics into routine geotechnical engineering practice requires an evaluation of methodologies that may be used for the assessment of 'unsaturated soil property functions.' Guidelines and recommendations need to be provided to practicing engineers. The guidelines need to take the form of 'engineering protocols' that define acceptable standards for engineering practice. 'Engineering protocols' for unsaturated soils engineering practice can be divided into 'preliminary design' protocols and 'final design' protocols. Both design levels involve the use of a variety of estimation procedures that have been proposed for various classes of geotechnical problems (e.g., unsaturated flow, shear strength, volume change, and distortion). The hierarchy in methodologies is based mainly on the costs and risks associated with a particular engineering project. In this paper, 'hierarchical levels' are suggested that take into consideration the cost of various direct and indirect methodologies for the determination of unsaturated soil properties. Recommendations and suggestions are provided for methods for the determination and use of the soil-water characteristic curves (SWCC) and consequently, for the computation of unsaturated soil property functions (USPFs). Primary attention is given to estimation procedures best known to the authors and most appropriate for geotechnical engineering practice. Key words: unsaturated soil mechanics, soil-water characteristic curves, unsaturated soil property functions, soil suction, engineering protocols, hierarchical levels. L'implementation de la mecanique des sols non satures dans la pratique de routine de la geotechnique implique une evaluation des methodologies qui peuvent etre utilisees pour la determination des >> fonctions des proprietes du sol non sature >>. Les ingenieurs praticiens doivent avoir acce's aux lignes directrices et aux recommandations. Les lignes directrices doivent prendre la forme de << protocoles d'ingenierie >> qui definissent les standards acceptables dans la pratique de l'ingenierie. Les protocoles d'ingenierie peuvent etre divises en protocoles de conception preliminaire et en protocoles de conception finale. Ces deux niveaux de conception impliquent l'utilisation d'une variete de procedures d'estimation qui ont ete proposees pour differentes categories de proble'mes geotechniques (ex : ecoulement non sature, resistance au cisaillement, changement de volume et distorsion). La hierarchie des methodologies est basee principalement sur les couts et les risques associes a' un projet d'ingenierie specifique. Dans cet article, des >> niveaux hierarchiques << sont suggeres qui tiennent compte des couts de plusieurs methodologies directes et indirectes servant a determiner les proprietes des sols non sature s. Des recommandations et suggestions sont presentees a propos desmethodes de determination et d'utilisation des courbes caracteristiques sol-eau << SWCC >>, ainsi que sur les calculs des fonctions des proprietes du sol non sature << USPFs >>. Une attention particuliere est donnee aux procedures d'estimation les mieux connues par les auteurs et les plus appropriees pour la pratique de la geotechnique. Mots-cles : mecanique des sols non satures, courbes caracteristiques sol-eau, fonctions des proprietes du sol non sature, succion du sol, protocoles d'ingenierie, niveaux hierarchique. [Traduit par la Redaction], Introduction The development of infrastructure to meet the needs of society commonly involves soils from above the groundwater table. These soils have negative pore-water pressures and are referred to as [...]

Field sampling was performed at a number of residential structures in the Denver metropolitan area for the purpose of assessing the extent of wetting below residential structures after construction and commencement of landscape irrigation. Total suction measurements using filter paper methods were undertaken on undisturbed samples. A similar data set from sites without previous development or irrigation was used to estimate the suction profile before the imposition of residential construction and landscape irrigation. Comparison of the postdevelopment profile measured at the residential structures to the predevelopment profile estimated using a site-specific procedure was used to assess the depth of wetting at each structure. Cumulative probability curves are presented for the depth of wetting arising from common residential landscape schemes and site drainage for the Denver area. The Denver-area data set was used to develop a method for assessment of depth of wetting. This method can be used to assess depth of wetting from residential development for other regions having different climatic conditions and landscape practices. DOI: 10.1061/(ASCE) 1090-0241 (2009) 135:2(169) CE Database subject headings: Expansive soils; Subsurface flow; Soil suction; Unsaturated soils; Residential location; Colorado; Irrigation; Urban areas.

A series of unsaturated soil triaxial tests were performed on four soils including sand, silt, and a low plasticity clay. Attempts were made to correlate unsaturated soil properties from these tests and data from the literature with soil-water characteristics curve (SWCC), soil gradation, and saturated soil properties. The feasibility of estimating unsaturated soil property functions from saturated soil properties, SWCCs and gradation data, is demonstrated. A hyperbolic model for estimation of the unsaturated soil parameter, [[PHI].sup.b], versus matric suction is presented. Shear induced volume change behavior was also studied, and results are included in this paper. Although not correlated with soil index properties, these shear-induced volume change data are important to complete stress- deformation analyses, and represent a significant addition to the existing data base of unsaturated soil properties. CE Database subject headings: Shear strength; Suction; Volume change; Unsaturated soils; Triaxial tests; Soil properties.

Abstract: To investigate the soil structure and mechanical behavior of an unsaturated expansive clay soil, triaxial and mercury intrusion tests have been performed and are presented in this paper. Also [...]

Water reuse and ground-water recharge can be used to meet the growing demands for water, particularly in arid regions. Ground-water recharge using fresh water or treated wastewater is most often accomplished by infiltration from surface basins. The water percolates through the unsaturated soil region to an underlying aquifer for storage and future use. In the case of wastewater, additional treatment occurs as the effluent flows through the soil. The system hydraulics of recharge basins have been examined through a combination of field and laboratory investigations. These studies indicate that infiltration rates and soil aquifer treatment of wastewater are influenced by soil type and soil profile characteristics, surface clogging material, pond depth, and wetting/drying cycle times. The surface-clogging layer was found to be susceptible to consolidation and to associated reduction in hydraulic conductivity under seepage forces.

The engineering properties of compacted soils are of primary importance in fill performance. However, for economic reasons, the achievement of a given relative compaction and compaction water content has become an end in itself for field compaction control. Although the profession has developed an understanding of the relationships between properties and compaction density/water content, it has become routine practice to use some combination of precedence and code rather than desired material properties to establish compaction specifications. Because of the heavy emphasis placed on relative compaction, it is extremely important that geotechnical practitioners and earthwork contractors recognize the deviations in field density that can occur as a result of typical differences in the compaction processes and in the methods of compaction control encountered. Variations in both the field density and the laboratory-determined reference maximum dry density arise from numerous sources. A corresponding spatial variability of relative compaction should therefore be anticipated. This paper provides a comprehensive evaluation of potential problems in compaction control, and addresses the sources of field variability in relative compaction.

Robert W. Day argues that the presence of loose debris or a disturbed zone at the bottom of the small-diameter boring is a serious disadvantage for Sandra L. Houston et al's method of in-situ test for collapsible soil. Sylvio R.M. Ferreira et al examine the techniques used with both apparatus and present data on these soils, focusing on the flooding method used and the comparison between in-situ collapse under a plate inside an auger boring and laboratory collapse obtained in an oedometer test.

Gravelly subgrade materials are frequently evaluated on the basis of laboratory testing on material passing the number 4 sieve size due to difficulties in obtaining representative samples and because laboratory testing of soils containing rock is more difficult or expensive. When the large aggregate is not considered in the evaluation process, it is quite possible to discard a material as being inappropriate as subgrade material when in fact it may be quite suitable. For example, the presence of rock or gravel materials may have an ameliorating effect for clayey soils having potential for expansion upon wetting. The effect of large aggregate on the moisture sensitivity of subgrade materials are reviewed. It is more difficult to establish field specifications and to conduct field inspections for compaction of subgrades containing large aggregate. The potential pitfalls in obtaining the desired relative compaction in the field are discussed. The various commonly used techniques in writing field specifications for compaction of materials containing rock or gravel are reviewed.

An evaluation of water sources and extent of wetting at a collapsible soil site is presented. The field and laboratory data were collected after distress of an existing structure was observed. The underlying soils at the site were highly variable in fines content, density, and degree of saturation. Because of the high variability of soil properties, suction contours were developed for the site to evaluate the extent of soil wetting. A relationship between soil suction and basic soil parameters was developed for use in constructing these contours. The depth of wetting obtained using the suction contours was consistent with other data at the site, including quantity of water introduced and standard penetration test results. Laboratory collapse curves were used to estimate the settlement at the site for the depth of wetting inferred from the suction contours. The computed settlements, taking into consideration partial wetting effect, were consistent with observed settlements of the structure.

The effect of varying percentages of large aggregate on the maximum dry density and optimum water content of clay is investigated through a series of laboratory compaction tests. Rock content (material retained on the No. 4 sieve) was varied from 0% to about 60% in the laboratory tests. The compaction tests are performed primarily using ASTM D698 method D, with replacement for oversized aggregate, i.e., the 'scalp-and-replace' method. The maximum dry density obtained from ASTM D698 method D is compared with the maximum dry density estimated from rock correction equations in ASTM method 4718, U.S. Bureau of Reclamation method 5515-89, and American Association of State Highway and Transportation Officials procedure T224. The optimum water content obtained from ASTM D698 method D is compared to the estimated optimum water content obtained from rock correction equations in ASTM method 4718. The data presented in this paper show that when soil fines are clayey, very significant differences in maximum dry density are obtained using scalp-and-replace procedures compared with the rock correction equations. The potential impact of these differences on construction compaction control are addressed.

A common underlying assumption in the development of soil-water characteristic curves (SWCCs) is that the soil is sufficiently stiff such that no changes occur in the volume of the soil associated with soil-suction change. A number of researchers recently recognized the importance of considering soil-volume changes in SWCCs; however, few researchers have evaluated the effect of volume change on the computed rate and degree of wetting/drying of unsaturated soils and the associated impact on computed soil-volume change response. This paper focuses on the impacts of considering soil-volume change in the determination of SWCCs for high-volume-change soils, with emphasis on the estimated unsaturated hydraulic conductivity function and response to wetting. Numerical simulations of unsaturated flow and suction-induced volume change were used to study the effect of consideration of volume change in the determination of SWCCs. Numerical analyses used laboratory-determined SWCCs with and without the inclusion of volume change measurements. The study results demonstrate that the impact of volume change consideration on SWCCs and the estimated unsaturated hydraulic conductivity function can be quite substantial for high-volume-change soils such as expansive clays. [ABSTRACT FROM AUTHOR]