An experimental investigation of the mechanical behaviour of an unsaturated gneiss residual soil

Futai, Marcos Massao; Almeida, M. S. S.

doi:10.1680/geot.2005.55.3.201

Cited by 60 publications

(40 citation statements)

References 18 publications

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“…The compression index of a second group of soils increased with matric suction. This was reported for loess soil (Adams and Wulfsohn, 1998;Kogho et al, 2001;Wang et al, 2002;Futai and Almeida, 2005) and for sandy soils (Futai and Almeida, 2005). Our results tend to agree with the second group.…”

Section: Variation Of Compression Index With Soil Texturesupporting

confidence: 90%

Quantifying the effect of matric suction on the compressive properties of two agricultural soils using an osmotic oedometer

et al. 2010

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The compaction of cultivated soils by agricultural machines considerably affects both the structure and physical properties of soil, thus having a major impact on crop production and the environment. Soil mechanical resistance is highly variable both in time and space because it depends on soil texture, soil porosity and soil water state (matric suction). This paper is devoted to the effect of soil matric suction on the compression index C c , which is one of the mechanical parameters that describes the soil mechanical resistance to compression. We performed oedometer compression tests to study the compression index of a loamy soil and a sandy clay, with matric suction control, by using the osmotic technique. Soil samples were prepared by compacting soil passed through a 2 mm sieve at dry bulk densities of 1.1 and 1.45 Mg m −3 . The mechanical stress and matric suction ranges considered corresponded to field condition, with vertical stress less than 800 kPa and matric suction less than 200 kPa. The results show that the compression index C c was constant or changed little with matric suctions for the two soils at different initial densities. For the loamy soil, the average compression index C c equals 0.73 for an initial bulk density of 1.1 Mg m −3 and 0.41 for 1.45 Mg m −3 for matric suction higher than 20 kPa. For the sandy clay, the average compression index C c is 0.35. From a practical point of view, our study shows that the mathematical determination of mechanical parameters should be standardized due to the S-shaped compression curves that may significantly impact the compression index estimation. The observation of constant compression index with matric suction is a useful result for modelling soil strain due to traffic and predicting the compaction of cultivated soils.

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Section: Variation Of Compression Index With Soil Texturesupporting

confidence: 90%

Quantifying the effect of matric suction on the compressive properties of two agricultural soils using an osmotic oedometer

et al. 2010

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“…While the yield stress increasing with increasing suction agrees with other published results (Alonso et al, 1990;Maãtouk et al, 1995;Wheeler & Sivakumar, 1995;Futai & Almeida, 2005), the shape of the yield locus is interesting. The yield locus shown in Fig.…”

Section: Pressure-volume Relationship During Isotropic Compression Unsupporting

confidence: 90%

“…Many researchers have postulated the existence of consistent compression characteristics for unsaturated soils (Alonso et al, 1990;Maãtouk et al, 1995;Wheeler & Sivakumar, 1995;Futai & Almeida, 2005). In order to validate this postulation it is necessary to confirm that the state of an unsaturated soil on yielding remains on a unique normal compression line for a given value of suction, and on a unique compression surface when the effect of suction is considered.…”

Section: Pressure-volume Relationship During Isotropic Compression Unmentioning

confidence: 99%

Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 1: wetting and compression behaviour

Sivakumar¹,

Sivakumar²,

Murray³

et al. 2010

Géotechnique

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Over the last 40 years considerable progress has been made in understanding the complex behaviour of unsaturated soils. Research using constitutive modelling has extended the critical state framework and the concept of yielding in saturated soils to encompass unsaturated soils experiencing suction. However, validation testing of the framework for unsaturated soils has shown disagreement with the basic propositions. The main reason for this disparity is the anisotropic properties of the soil specimens tested as a result of preparation using one-dimensional compaction. The paper describes the detailed testing carried out to justify this statement. As part of the work presented, samples of unsaturated kaolin were prepared using isotropic compression. The suctions in these samples were reduced to predefined values by wetting under low isotropic loading. The pore size distributions, the pressure-volume relationships and yielding under subsequent isotropic loading are compared with tests on samples prepared by statically compressing kaolin into a one-dimensional compaction mould. The anisotropically compressed samples had initial water contents and specific volumes similar to those of the isotropically prepared samples and were also tested under reducing suctions; they exhibited distinctly different behaviour when tested under similar conditions. The results obtained from the isotropically prepared and tested samples have shown, probably for the first time, the existence of a unique normal compression surface that is not dependent on the initial conditions of the samples. The shape of the loading-collapse (LC) yield locus is shown to be different from the generally accepted form.Au cours des 40 dernières années, on a réalisé des progrès considérables dans la compréhension du comportement complexe des « sols non saturés ». Des travaux de recherche faisant usage d'une modélisation constitutive ont déterminé l'expansion du cadre de l'état critique ainsi que le concept de l'affaissement dans les sols saturés, en incorporant les sols non saturés soumis à une aspiration. Toutefois les essais de validation du cadre relatif aux sols non saturés présentent des divergences avec les thèses de base. La principale raison de cette disparité tient aux propriétés anisotropes des spécimens de sol testés en conséquence de la préparation faisant usage d'un compactage unidimensionnel. La présente communication décrit les essais détaillés qui ont été effectués à l'appui de cette thèse. Dans le cadre des travaux présentés, on prépare des échantillons de kaolin non saturé par compression isotrope. On compare ensuite la distribution des diamètres de pores, les rapports pression /volume et le fléchissement sous l'effet des charges isotropes ultérieures avec des tests effectués sur des échantillons préparés par la compression statique de kaolin dans un moule de compactage unidimensionnel. Initialement, la teneur en eau et le volume massique des échantillons à compression anisotrope sont similaires à ceux des échantillons ayant fait l'objet d'un...

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“…However, the intercept value drops significantly for the suction of 300 kPa. An increase in ì(s) with suction is reported elsewhere (Alonso et al, 1990;Maãtouk et al, 1995;Wheeler & Sivakumar, 1995;Futai & Almeida, 2005), but it is not unusual for the intercept to exhibit a reduction as shown, although the reason for this is unclear. Some early work on unsaturated soils had identified the variable effect of suction on the apparent cohesion induced by suction (Fredlund et al, 1978;Escario & Saez, 1986).…”

Section: Resultsmentioning

confidence: 69%

Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 2: performance under shear loading

Sivakumar

Sivakumar²,

Boyd³

et al. 2010

Géotechnique

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Validation of a framework for unsaturated soil behaviour has frequently resulted in disagreement with basic propositions. A primary reason for this disparity is considered to be attributable to the anisotropic properties of the soil specimens tested as a result of preparation using one-dimensional compaction. As part of the work presented, comparison is made between tests on samples of unsaturated kaolin prepared at identical specific volumes and specific water volumes using isotropic compression and one-dimensional compression. The suctions in the samples were reduced to predefined values by wetting under low isotropic loading in a triaxial cell. The samples were then taken through various stress paths to failure, defined as the critical state strength, while the suctions were held constant. Stress path tests were also performed on samples without reducing the suction to predefined values. In the latter, constant water mass tests, the suctions were allowed to vary and were measured using a psychrometer. The results of the tests at critical state are compared with the propositions of Wheeler and Sivakumar. The shear strengths of samples with isotropic previous history are shown to be significantly greater than those of samples with one-dimensional stress history when plotted against the mean net stress. The normal compression lines, critical state lines and yield characteristics are also shown to be significantly influenced by the previous stress history and are shown to be different for isotropically and one-dimensionally prepared samples.

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An experimental investigation of the mechanical behaviour of an unsaturated gneiss residual soil

Cited by 60 publications

References 18 publications

Quantifying the effect of matric suction on the compressive properties of two agricultural soils using an osmotic oedometer

Quantifying the effect of matric suction on the compressive properties of two agricultural soils using an osmotic oedometer

Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 1: wetting and compression behaviour

Mechanical behaviour of unsaturated kaolin (with isotropic and anisotropic stress history). Part 2: performance under shear loading

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