Propriedades Fsicas dos Solos

SumrioTexturaTamanho de Gro e Distribuio GranulomtricaForma da PartculaLimites de AtterbergConsideraes sobre Anlise GranulomtricaConsideraes sobre Sedimentao

1. Textura dos Solos

1.1 TexturaA textura de um solo sua aparncia ou sensao ao toque e depende dos tamanhos relativos e formas das partculas, bem como da faixa ou distribuio desses tamanhos.

Peneiramento Sedimentao

1.2 Caractersticas(Holtz and Kovacs, 1981)

2. Tamanho de Gro e Distribuio Granulomtrica

2.1 Tamanho de GroPedreguhoAreiaSilteArgila4.75Unit: mm(Holtz and Kovacs, 1981)USCSBS0.0752.00.060.002USCS: Unified Soil ClassificationBS: British Standard

Nota:Frao argilaArgilo-mineraisExemplo:Caolinita, Ilita, Montmorilonita, etc.Exemplo:Uma pequena partcula de quartzo pode ter tamanho similar ao de argilo-minerais.

2.2 Distribuio Granulomtrica(Das, 1998)(Head, 1992)Peneira

2.2 Distribuio Granulomtrica (Cont.)EnsaiosPeneiramento Sedimentao(Head, 1992)

2.2 Distribuio Granulomtrica (Cont.)Escala logartmica(Holtz and Kovacs, 1981)Tamanho efetivo D10: 0.02 mmD30: D60:

2.2 Distribuio Granulomtrica (Cont.)Descreve a formaExempo: Bem graduada

Critrios

PerguntaQual o Cu para um solo com um nico tamanho de gro?

PerguntaPerguntaQual o valor de Cu para um solo com um nico tamanho de gro?

Tamanho de partcula% acumalada passanteDistribuio granulomtrica

2.2 Distribuio Granulomtrica (Cont.)Aplicaes na EngenhariaAuxilia a sentir a textura do solo (que solo esse) e tambm ser empregada na classificao de solos (prximo assunto).Pode ser usada para definir a faixa granulomtrica especificada para filtro de um dreno (para evitar a colmatao do mesmo) Pode ser um critrio de seleo de materiais de enchimento e aterros de barragens, materiais para sub-base e base de pavimentos e agregados para concreto de CP e misturas asflticas.O Dimetro efetivo, D10, pode ser correlacionado com a condutividade hidrulica (descrevendo a permeabilidade de solos). (Equao de Hazen).(Nota: controlada pelas partculas menores)A distribuio granulomtrica mais importante para os solos granulares.

3. Forma da Partcula

Importante para solos granularesPartculas angulares maior atritoPartculas arredondadas menor atritoNotar que as partculas de argila tm formato lamelar.ArredondadaSubarredondadaSubangularAngular(Holtz and Kovacs, 1981)Solos granulares

4. Limites de Atterberge ndices de Consistncia

4.1 Limites de AtterbergA presena de gua nos solos finos pode afetar significativamente o comportamento de engenharia, portanto, so necessrios ndices de referncia que evidenciem esses efeitos.(Holtz and Kovacs, 1981)Em %

4.1 Limites de Atterberg (Cont.)Solo secoMistura fluida solo-guaTeor de umidade crescente

4.2 Limite de Liquidez-LLMtodo de Casagrande(ASTM D4318-95a)O Professor Casagrande normatizou o ensaio e desenvolveu o aparelho para determinao do limite de liquidez.MateriaisSolo passando na peneira No.40 (0,425 mm).gua destilada

4.2.1 Mtodo de CasagrandeN=25 golpesAbertura da ranhura = 12,7mm (0.5 in)(Holtz and Kovacs, 1981)AparelhoO Limite de Liquidez o teor de umidade para o qual a ranhura de solo se fecha com 25 golpes, no aparelho de Casagrande.

4.2.1 Mtodo de Casagrande (Cont.)Das, 1998

4.3 Limite de Plasticidade - LPO limite de plasticidade, LP, o teor de umidade no qual um cilindro de solo com 3,2 mm de dimetro comea a trincar quando moldado.ASTM D4318-95a, BS1377: Part 2:1990:5.3(Holtz and Kovacs, 1981)

4.4 Limite de Contrao - LCDefinio do LC:Teor de umidade abaixo do qual o solo no mais muda de volume ao variar seu teor de umidade(Das, 1998)SL

4.4 Limite de Contrao - LC (Cont.)(Das, 1998)Volume de solo: ViMassa de solo: M1Volume de Solo: VfMassa do solo: M2

4.4 Limite de Contrao - LC (Cont.)Embora o limite de contrao fosse bastante usado durante os anos 1920s, atualmente considerado como sujeito a elevada incerteza e portanto sua determinao no mais comum.

Um dos maiores problemas do ensaio de limite de contrao que a magnitude da contrao depende no apenas do tamanho do gro mas tambm da estrutura inicial do solo. O procedimento padro consiste em iniciar o ensaio com um teor de umidade prximo (mas inferior) ao LL. Entretanto, especialmente nas argilas siltosas e arenosas, isto resulta em valores de LC superiores ao LP, o que no tem sentido. Casagrande sugere que o teor inicial de umidade seja ligeiramente maior do que o LP, se possvel, mas reconhece-se que nesta condio difcil evitar a aprisionamento de bolhas de ar no solo moldados. (Holtz and Kovacs, 1981)

4.5 Tpicos Valores dos Limites de Atterberg(Mitchell, 1993)

4.6 ndicesIndice de Plasticidade IP Para descrever o intervalo de teor de umidade em que um solo plsticoIP = LL LPL

ndice de Consistncia IC

LC

4.6 Indices (Cont.)Atividade A (Skempton, 1953)

Argilas de atividade normal: 0,75

4.7 Engineering ApplicationsSoil classification (the next topic)

The Atterberg limits are usually correlated with some engineering properties such as the permeability, compressibility, shear strength, and others.In general, clays with high plasticity have lower permeability, and they are difficult to be compacted.The values of SL can be used as a criterion to assess and prevent the excessive cracking of clay liners in the reservoir embankment or canal.The Atterberg limit enable clay soils to be classified.

5. Some Thoughts about the Sieve AnalysisThe representative particle size of residual soilsThe particles of residual soils are susceptible to severe breakdown during sieve analysis, so the measured grain size distribution is sensitive to the test procedures (Irfan, 1996).

Wet analysisFor clean sands and gravels dry sieve analysis can be used.If soils contain silts and clays, the wet sieving is usually used to preserve the fine content.

6. Some Thoughts about the Hydrometer Analysis Stokes law

(Compiled from Lambe, 1991)

8. ReferencesMain References:Das, B.M. (1998). Principles of Geotechnical Engineering, 4th edition, PWS Publishing Company. (Chapter 2)Holtz, R.D. and Kovacs, W.D. (1981). An Introduction to Geotechnical Engineering, Prentice Hall. (Chapter 1 and 2)Others:Head, K. H. (1992). Manual of Soil Laboratory Testing, Volume 1: Soil Classification and Compaction Test, 2nd edition, John Wiley and Sons.Ifran, T. Y. (1996). Mineralogy, Fabric Properties and Classification of Weathered Granites in Hong Kong, Quarterly Journal of Engineering Geology, vol. 29, pp. 5-35. Lambe, T.W. (1991). Soil Testing for Engineers, BiTech Publishers Ltd.Mitchell, J.K. (1993). Fundamentals of Soil Behavior, 2nd edition, John Wiley & Sons.

Talk about the difference between the clay-size particle or clay minerals.Please remind students about the oxymoron of the cohesion and cohesionless.Change this tableMention sieve analysis and hydrometer analysis for different size of soilsThere is not distinguish for silt and clay in the USCS system.It is not necessary to use the full set of sieves, but the particle size should be distinguished.Wet sieving:According to the British standard, dry sieving may be carried out only on materials for which this procedure gives the same results as the wet-sieving procedure. This means that it is applicable only to clean granular materials, which usually implies clean sandy or gravelly soils-that is, soils containing negligible amounts of particles of silt or clay size. Normally the wet-sieving procedure (section 4.6.4) should be followed for all soils (Head, 1992).Effective size (D10): This parameter is the diameter in the particle-size distribution curve corresponding to 10% finer. The effective size of a granular soil is a good measure to estimate the hydraulic conductivity an ddrainage through soils.The comparison between the fall cone test and the Casagrande test, Page. 79 (Heads book)The definition of the liquid limit is dependent on he point at which the soil begins to acquire a recognizable shear strength (about 1.7 kN/m2) (Head, 1992).The one-point methods are useful as rapid test procedures, or when only a very small amount of soil is available and when a result of lesser accuracy is acceptable (Head, 1992).Drying, even air drying at laboratory temperature, can cause irresible changes in the physical behavior of some soils, especially tropical residuals, which can result in dramatic changes in their plasticity properties (Head, 1992).ASTM D4318-95a. The sample is processed to remove any material retained on a 0.425 mm. (No.40) sieve .Both the type and amount of clay in a soil influence the properties, and the Atterberg limits reflect both of these factors.From MitchellThe plastic limit has been interpreted as the water content below which the physical properties of the water no longer correspond to those of free water (Terzaghi, 1925) and as the lowest water content at which the cohesion between particles or groups of particles is sufficiently low to allow movement, but sufficiently high to allow particles to maintain the molded position (Yong and Warkentin, 1966). If you have different clay minerals, you will have different Atterberg limit.The PI is useful in engineering classification of fine-grained soils, and many engineering properties have been found to empirically correlates with the PI.There is fair/good correlation of the activity and the type of clay mineral (chapter 4)However, the Atterberg limits alone are usually sufficient for these purposes, and the activity provides no really new information.In general, clays of high plasticity are likely to have a lower permeability, to be more compressible and to consolidate over a longer period of time under load than clays of low plasticity. High-plasticity clays are more difficult to compact when used as fill materials.Relate to the permeability.The values of SL are particular useful to in connection with the placing of puddle clay in reservoir embankments or canal linings. To prevent excessive cracking is some drying out of the clay is likely to occur, the shrinkage range can be limited. Clay minerals and clay-size particles