Search

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 [...]

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.

It has become increasingly difficult to provide a complete, practical geoscience education to students and the public, as teachers may have to cover many scientific disciplines, general science textbooks only contain a cursory review of geoscience and there is often a lack of financial and resource support. Some of these problems could be alleviated through partnerships between colleges, universities, local school districts and community agencies.

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.

The FWD testing method was applied on pavements with both laboratory and field measurements. While the measurements of both approaches cannot be expected to be the same, the dependability of the FWD method was questioned because measurements should consider the pavement's length as an average rather than a single measurement. However, there is evidence from field trials that the FWD is a reliable method since it takes into account the weighted-average modulus for the weight and volume of pavement subgrade materials.

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.

A comparison of the results obtained from laboratory and field tests of a pavement structure is discussed. The laboratory procedure includes the application of pulsating loads on the structure through diametral and triaxial tests while the field testing procedure employs the falling weight deflectometer (FWD) method, a technique widely used by designers because of its reliability. Results from both tests indicate that FWD is capable of accurate moduli analysis at low cost as compared to conventional laboratory programs.