Air entrapment and differential swelling as factors in the mellowing of molded soil during rapid wetting

Grant, C. D.; Dexter, A. R.

doi:10.1071/sr9900361

Cited by 39 publications

(29 citation statements)

References 29 publications

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“…This apparent differences in wetting behaviour between both soils may also be the results of occlusion and change in roughness acting on both soils also, as discussed below. The reduced rate of swelling observed simultaneously with the decreased maximum pressure attained inside the aggregate can explain the reduction of slaking (reduced loss of matter) following the addition of organic matter (Tables 2Á4), as reported by others (Monnier 1965;Grant and Dexter 1990). This restriction of amended aggregate swelling may be due to improved cohesion of wet aggregates, which leads to fewer internal stresses causing instability.…”

Section: Discussionsupporting

confidence: 64%

“…It may also be due to slower water entry within the aggregate, causing less swelling of the aggregate. We cannot, however, conclude whether the processes acted synergistically or independently (Grant and Dexter 1990). At the micro-aggregation level, the results presented in Table 6 show that the fraction of dispersed clay is positively related to the pressure and swelling generated by wetting.…”

Section: Discussionmentioning

confidence: 89%

“…Rapid wetting of dry aggregates generally brings about a rupture due either to pressure build-up generated by air trapped inside the individual aggregate exceeding its cohesion capacity (Concaret 1967a;Le Bissonnais 1988) or differential stresses generated by swelling that create planes of weakness within the aggregate (Panabokke and Quirk 1957;Emerson 1977;Le Bissonnais 1989). Recent research has confirmed that these two factors work synergistically to cause structural degradation (Grant and Dexter 1990;Emerson 1991), or that one of these two factors may be predominant. According to Caron et al (1996) a decrease in structural stability is attributable more to the increased water entry into the aggregate than to a change in its cohesion.…”

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confidence: 99%

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Aggregate slaking during rapid wetting: Hydrophobicity and pore occlusion

Zaher¹,

Caron

2008

Can. J. Soil. Sci.

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Zaher, H. and Caron, J. 2008. Aggregate slaking during rapid wetting: Hydrophobicity and pore occlusion. Can. J. Soil Sci. 88: 85Á97. The slaking process after rapid wetting is a key factor controlling soil structural stability in dry soil, and an understanding of the relative importance of the different mechanisms involved in slaking may help in the design of management strategies aimed at maintaining a stable surface soil structure. Slaking has been linked to, among other factors, rapid pressure build-up in aggregate, and previous work has emphasized the role of organic matter to hamper that pressure build-up, possibly due to hydrophobicity, reducing rapid water entry within aggregates and hence the build-up. This study emphasizes this latter aspect linked to slaking. The evolution of the intra-aggregate pressure, the matter lost by slaking and the expelled air after rapid wetting of two soils of different textures (clay loam soil and silty-clay loam soil) amended with different types of paper sludge were studied. Hydrophobicity effects were also studied using a tensio-active solution. The results of these experiments showed that when aggregates were submitted to sudden wetting, those treated with paper sludge had an improved resistance to the destructive action of rapid wetting. The lower pressures measured in the aggregates from the amended soils and having less slaking resulted most likely from slow water entry and reduced swelling. Detailed investigation on the link between hydrophobicity and water entry revealed that the true hydrophobic effect (modification of contact angle) was non-existent for the silty-clay loam and minor for the clay loam. This study, rather, suggests that changes in the water potential at the wetting front following organic matter addition and aggregate immersion most likely depend on pore occlusion and on changes in pore surface roughness.Key words: Aggregate stability, organic matter, slaking, pressure, swelling, wettability Zaher, H. et Caron, J. 2008. De´sagre´gation du sol apre`s mouillage rapide : hydrophobicite´et occlusion des pores. Can. J. Soil Sci. 88: 85Á97. La de´sagre´gation apre`s mouillage rapide joue un roˆle capital dans le maintien de la stabilite´structurale du sol et comprendre l'importance relative des diffe´rents me´canismes a`son origine pourrait faciliter l'e´laboration de strate´gies de gestion visant a`stabiliser la structure du sol de surface. On a notamment associe´la de´sagre´gation a`l'e´le´vation rapide de la pression dans les agre´gats et des recherches ante´rieures ont mis en relief le roˆle de la matie`re organique qui, peut-eˆtre ac ause de son hydrophobicite´, ralentit la pe´ne´tration de l'eau dans les agre´gats, donc la hausse de pression. La pre´sente e´tude souligne cet aspect, associe´a`la de´sagre´gation. Les auteurs ont examine´l'e´volution de la pression dans les agre´gats, la matie`re perdue lors du phe´nome`ne et l'air expulse´apre`s mouillage rapide d'un sol de deux textures (loam argileux et loam limoneux-argileux) auquel on avait aj...

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Section: Discussionsupporting

confidence: 64%

Section: Discussionmentioning

confidence: 89%

mentioning

confidence: 99%

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Aggregate slaking during rapid wetting: Hydrophobicity and pore occlusion

Zaher¹,

Caron

2008

Can. J. Soil. Sci.

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“…For an aggregate to slake, the pressure buildup due to entrapped air exerted on it must overcome the intrinsic force of cohesion holding the structural units together (Grant and Dexter, 1990;Zaher et al, 2005). Kemper and Rosenau (1986) showed that the antecedent moisture content of the soil aggregates before aggregate stability determination controls the severity of the disruption.…”

Section: Theorymentioning

confidence: 98%

Modelling slaking sensitivity to assess the degradation potential of humid tropic soils under intense rainfall

2010

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In the humid tropics, soil erosion due to the impact of high-intensity tropical rainfall is one of the important environmental problems. A quick assessment of slaking sensitivity of soils that are frequently subjected to the fast wetting of intense rainfall of the humid tropics is necessary for the selection of appropriate soil management practices to avoid soil structure deterioration that results in runoff, seal formation, erosion and eventual degradation. Unfortunately, field and laboratory measurements of slaking sensitivity are tedious, time consuming and expensive. Therefore, a slaking sensitivity ranking framework using readily available soil data, namely, clay content, organic matter content, exchangeable sodium percentage (ESP) and cation exchange capacity (CEC) determined to be important in slaking sensitivity and structural degradation under intense rainfall was developed. The ranking framework was subsequently used to classify 23 agriculturally important Trinidadian soils into slaking sensitivity classes for management recommendation. A simple mathematical model that provides a rapid assessment of slaking sensitivity was also developed using the soil data of 14 out of the 23 soils and subsequently tested on the remaining nine soils. Our results suggest that about 80 per cent or more of the soils are highly sensitive to slaking pressures, highly vulnerable to degradation and require management practices that reduce the rate of wetting and thus degradation of aggregates under intense rainfall. The developed model performed with a high degree of accuracy as the predicted values were in close agreement with measured values (r ¼ 0Á93). This suggests that the model gives a good indication of the structural degradation vulnerability of the soils studied under the conditions applied and criteria used. The model is, therefore, recommended for use in the tested humid tropical soils. However, more comprehensive testing is required on a broader range of soils prior to its more widespread application in other climatic conditions.

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“…T he soil stability also influenced by the rate at which wetting takes place, the pressure of entrapped air and the extent of differential swelling (Grant & Dexter, 1990). When stability is measured under relatively wet condition, it is noted that it is decreasing with water content (Kay & Dexter, 1990;Perfect et al, 1990;Gollany et al, 1991).…”

Section: Introductionmentioning

confidence: 99%

Aggregate stability of four soils as evaluated by different indices

Nweke¹,

Nnabude²

2015

JEBAS

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KEYWORDS Aggregate stabilityGeometric mean-weight Diameter Mean-weight diameter ABSTRAC TIn present study, aggregate stability of four soils viz Entisol, Ultisol and t wo Inceptisols were evaluated usin g different indices. Soil samples from the depth of 0 -25cm were collected from cultivated and adjacent fallow lands at the four different sites located, at Nsukka area of southeastern, Nigeria. The soil samples were air-dried at room temperature and then were separated into five aggregate fractions i.e. 5 -2mm, 2-1mm, 1-0.5mm, 0.5-0.25mm and > 0.25mm. Aggregate stability assessments were performed according to the methods of mean-weight diameter and geometric mean-weight diameter which were determined by both dry and wet sieved fractions. T he results of the study showed that aggregation of the cultivated soils were less stable than the fallow soils. Furthermore, the aggregation of the cultivated soil disintegrated faster than those of the fallow soils when they came in contact with water. T he meanweight diameter (MWD) result of the soil aggregates showed that cultivation reduced the aggr egation stability of Nsukka Entisol for dry sieved samples an d Inceptisol at Eha-Amufu for wet sieved samples. T he mean-weight diameter of wet sieved aggregates though, generally not significant showed that percentage increases due to cultivation were 6.3, 3.2 and 2.9 percent for Entisol at Nsukka, Ultisol at Nsukka and Inceptisol at Ikem respectively and 50.0 percent relative decrease for Inceptisol at EhaAmufu. Geometric mean-weight diameter (GMD) result of both dry and wet sieved samples showe d that cultivation reduced the aggregation stability of Nsukka Entisol, Ultisol, Inceptisol at Eha-Amufu and no effect on Inceptisol at Ikem.

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Air entrapment and differential swelling as factors in the mellowing of molded soil during rapid wetting

Cited by 39 publications

References 29 publications

Aggregate slaking during rapid wetting: Hydrophobicity and pore occlusion

Aggregate slaking during rapid wetting: Hydrophobicity and pore occlusion

Modelling slaking sensitivity to assess the degradation potential of humid tropic soils under intense rainfall

Aggregate stability of four soils as evaluated by different indices

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