Soil Classification

Prepared by: Jodin MakindaLecture 4: Soil Classification 2Learning Outcomes:At the end of this lecture students will be able: to explain and outline the Atterberg Limit teststo analyze the results obtained.

Prepared by: Jodin Makinda

Prepared by: Jodin MakindaProblem Statement The changes in engineering behavior of soil affected civil engineering structures and human lives


Prepared by: Jodin MakindaEarth DisastersTrain tracks north of Seattle, WA, in January of 1997, mud swept a freight train into Puget Sound. (Photograph by Mike Siegel, The Seattle Times.)


Prepared by: Jodin MakindaEarth DisastersBukit Antarabangsa, 2008


Prepared by: Jodin MakindaEarth DisastersRibut Greg (24 December 1996), Keningau Sabah


Prepared by: Jodin MakindaEarth DisastersJalan Tamparuli-Ranau (Km 82.1) Source: JKR Sabah


Prepared by: Jodin MakindaEarth DisastersPos Dipang Perak (1996). Source: JKR Sabah


Prepared by: Jodin MakindaEarth DisastersKg Bondulon, Jalan Sepangar, Sabah (Source: JKR Sabah)


Prepared by: Jodin MakindaIntroductionAs mentioned in previous lecture, while dry sieve method is suitable for coarse grained soil (gravel and sand), hydrometer method can be used to determine the sieve analyze of small particles (clay & silt)Another valuable techniques for analyzing cohesive soils is by the use of Atterberg Limits


Prepared by: Jodin MakindaIntroductionAtterberg Limits is introduced by Prof. Dr. Albert Mauritz Atterberg (18461916) was a Swedish chemist and agricultural scientist.

Atterberg was the first to suggest the limit

Prepared by: Jodin MakindaWhy Atterberg Limit?The Atterberg Limits allow engineers to classify soils into their applications For instance one soil may have applications in sub-bases of roads, where another soil may be better suited for foundations of buildings When a soil becomes a viscous fluid, the soil will begin to flow under its own weight (Slope Failure)


Prepared by: Jodin MakindaAtterberg Limits TheoryIf the water content in a dry soil is gradually increased, it will change from solid to semi-solid to plastic to liquid statesThe 4 states are also known as consistency, and the soil properties as it passes these states change drastically


Prepared by: Jodin MakindaAtterberg Limit Theory4 states of consistency: Solid, Semi-Solid, Plastic and Liquid statesIf the water content in a dry soil is gradually increased, it will change from solid to semi-solid to plastic to liquid statesSEMI SOLID STATE


Prepared by: Jodin MakindaThinkWhat will happen if a soil sample in a liquid state is gradually dried out in an oven?


Prepared by: Jodin MakindaAnswerLiquidDryingWetting


Prepared by: Jodin MakindaAtterberg LimitsThe 4 states are divided by the Atterberg Limits:Liquid limit (LL) = dividing liquid and plastic statesPlastic limit (PL) = dividing plastic and semisolid statesShrinkage limit (SL) = dividing semisolid and solid statesLL, PL and SL are quantified in water content, w (i.e moisture content) and can be determined in lab tests


Prepared by: Jodin MakindaDetermination of LL (Casagrande)Procedure (LL)Soil sample is mixed with water, placed in the Casagrande cup and cut at the center by the grooving tool . The cup is raised and dropped repeatedly.When the cut closes the , number of drops is recorded and a moisture content of the sample is processed. Repeating the procedure provides enough data to plot on a linear vs semi-log scale. From the plot, the moisture content at 25 drops defines the Liquid Limit


Prepared by: Jodin MakindaDetermination of LL (Casagrande)


Prepared by: Jodin MakindaDetermination of LL (Casagrande)The Casagrande cup method of determining the LL has many shortcoming. Two of these are:The tendency of soils of low plasticity to slide and liquefy with shock in the cup, rather than to flow plasticallySensitivity to operator and to small differences in apparatus


Prepared by: Jodin MakindaExample 3.1 A liquid limit test conducted on a soil sample in the Casagrande cup device gave the following result:

No of blows1019232740Water content (%)60.045.239.836.5 25.2

Determine the liquid limit (LL) of the soil.


Prepared by: Jodin MakindaAnswer


Chart2

60

45.2

39.8

36.5

25.2

No of Blow

Moisture Content (%)

Sheet1

1060

1945.2

2339.8

2736.5

4025.2

Sheet1

0

0

0

0

0

No of Blow


Sheet2

Sheet3

Prepared by: Jodin MakindaAnswer25 blowsLL = 38%Moisture content at 25 blows = 38% (LL)


Chart2

60

45.2

39.8

36.5

25.2

No of Blow


Sheet1

1060

1945.2

2339.8

2736.5

4025.2

Sheet1

0

0

0

0

0

No of Blow


Sheet2

Sheet3

Prepared by: Jodin MakindaDetermination of LL (Fall Cone)ProcedurePrepare the soil mixed, place soil sample in the penetration cup Low the penetration cone slightly touching the surface of the soil before the cone penetrometer is released and penetration depth (in mm) is taken.Repeating the procedure provides enough data to plot on a semi-log vs semilog scale or linear vs. linear scale. From the plot, the moisture content at 20 mm depth penetration defines the Liquid Limit


Prepared by: Jodin MakindaExample 3.2In a liquid limit test on a fine-grained soil, using a cone penetrometer, the following results were recorded.

Cone Penetration (mm)15.917.719.120.321.5Water content (%)32.642.951.659.866.2

Determine the liquid limit of the soil


Prepared by: Jodin MakindaAnswer 3.2 (linear vs linear) Plot Penetration Vs Water content on graph paperCone Penetration (mm)15.917.719.120.321.5Water content (%)32.642.951.659.866.2


Prepared by: Jodin MakindaAnswer 3.2 (linear vs linear)


Chart1

15.9

17.7

19.1

20.3

21.5

Water content (%)

Penetration (mm)

Sheet1

Moisture Content (%)Penetration (mm)

32.615.9

42.917.7

51.619.1

59.820.3

66.221.5

Sheet1

0

0

0

0

0

Water content (%)

Penetration (mm)

Sheet2

Sheet3

Prepared by: Jodin MakindaAnswer 3.2 (linear vs linear)57%Moisture content at 20 mm penetration = 57% (LL)


Chart1

15.9

17.7

19.1

20.3

21.5

Water content (%)

Penetration (mm)

Sheet1


32.615.9

42.917.7

51.619.1

59.820.3

66.221.5

Sheet1

0

0

0

0

0

Water content (%)

Penetration (mm)

Sheet2

Sheet3

Prepared by: Jodin MakindaAnswer 3.2 (linear vs linear) Plot Penetration Vs Water content on Semilog-Semilog paperCone Penetration (mm)15.917.719.120.321.5Water content (%)32.642.951.659.866.2


Prepared by: Jodin MakindaAnswer 3.2 (Semilog vs semilog)Moisture content at 20 mm penetration = 57% (LL)


Chart2

15.9

17.7

19.1

20.3

21.5

Water content (%)

Penetration (mm)

Sheet1


32.615.9

42.917.7

51.619.1

59.820.3

66.221.5

Sheet1

Water content (%)

Penetration (mm)

Sheet2

Sheet3

Prepared by: Jodin MakindaDetermination of PLThe moisture content of a soil which can be formed into a ball, then rolled to a 1/8-inch (3mm) thread only once before crumbling


Prepared by: Jodin MakindaDetermination of LLMoisture content (w) is calculated as:

w = Wet soil Dry soil (%) Dry soil

Orw = Wwater(%) Wsoil


Prepared by: Jodin MakindaDetermination of SLThe shrinkage limit (SL) is the water content where further loss of moisture will not result in any more volume reduction The shrinkage limit is much less commonly used than the liquid limit and the plastic limit.


Prepared by: Jodin MakindaShrinkage LimitWet the soil sample. Place in another dish coated with petroleum jelly in 3 parts, weigh and set to dry and weigh againRemove the oven-dried soil pat, and replace the void with mercury, in addition the weight and volume of the empty shrinkage dish is determined.

SL = w 100 [ (V-V0)w / M0 ]

Where w = water content of wet soil, V = volume of wet soil, V0 = volume of oven-dried soil pat , w = density of water, M0 = mass of oven dried soil pat.


Prepared by: Jodin MakindaAnalysis of Atterberg LimitsPlasticity Index (PI) = LL PLThe Casagrande Plasticity Chart is made by plotting the plasticity index (PI) versus the liquid limit (LL).A method for determining the type of fines.


Prepared by: Jodin MakindaAnalysis of Atterberg LimitsThe A-line on the Plasticity Chart separates the clays from the silts . A-line equation;PI = 0.73 (LL-20) Any values the A-line or above will be classified as clay (C). And values below the A-line will be classified as silt (M). Materials whose limits plot within the cross-hatched area will be dually classified.


Prepared by: Jodin MakindaAnalysis of Atterberg LimitsThe B-line, of LL = 50 percent, separates the high compressible from the low compressible fine-grained soils. If the limits plot on the B-line or the right, the material will be high compressible (high LL) and given H as Secondary letter.If the limits plot to the left of the B-line, the material will be classified as low compressible (low LL) and given L as Secondary letter.B-line


Prepared by: Jodin MakindaAny question so far??


Prepared by: Jodin MakindaExample 3.1 and 3.2Given that the Plastic Limit (PL) for soils in previous Example 3.1 and 3.2 are as follow. Classify the soils using Plasticity Chart.

ExampleLL(%)PL(%)Plasticity Index (PI)Soil Classification3.138283.25725


Prepared by: Jodin MakindaAnalysis of Atterberg LimitsA measure of soil strength using the Atterberg Limits is known as liquidity index (LI) , expressed as LI = (w-PL)/(PI) Or

where w is the natural water content.

LI Value Description of soil strengthLI < 0 Semisolid state high strength, brittle, sudden fracture is expected0

Prepared by: Jodin MakindaAnalysis of Atterberg LimitsThe degree of plasticity of clay fraction is termed the activity of the soil.Activity, A = PI / % Clay

From the activity one can predict the dominant clay type present in a soil sample. High activity signifies large volume change when wetted and large shrinkage when dried and are very reactive chemically Normally, activity of clay is between 0.75 and 1.25. It is assumed that the plasticity index is approximately equal to the clay fraction (A = 1). When A is less than 0.75, it is considered inactive. When it is greater than 1.25, it is considered active

MineralsActivityMuscoviteKaoliniteIlliteMontmoroillonite0.250.400.90>1.25

SoilsActivityKaolin clayGlacial clay and loessMost British clayOrganic estuarine clay0.4-0.50.5-0.75

0.75-1.25>1.25


Prepared by: Jodin MakindaExample 3.3After a series of laboratory tests, the following data were established for a fine soil:LL = 45%PL = 18%Clay content = 24.2%

Classify the soilCalculate the activity of the soilDetermine the liquidity index of the soil when its natural moisture content is 29%


Prepared by: Jodin MakindaAnswer 3.3Using plasticity chart (LL=45, PI = 27), the soil is classified as CL (clay of low liquid limit)Activity, A = PI/% clay = (45-18)/24.1 =1.16LI = (29-18)/(45-18) x 100%= 41%


Prepared by: Jodin MakindaConclusionsFine-grained soils can exist in one of four states: solid, semi-solid, plastic and liquidWater is the agent that is responsible for changing the states of soilsA soil gets weaker if its water content increasesLL, PL and SL are defined on the water content that causes a change of state


Prepared by: Jodin MakindaConclusionsThe PI defines the range of water content for which the soil behaves like a plastic materialsThe LI gives a measure of strengthThe A gives a measure of degree of plasticity, reactivity and possible minerals / clay typesThe soil strength is lowest at the liquid state and highest at the solid state


Prepared by: Jodin MakindaThe End


Prepared by: Jodin MakindaDiscussionIn a laboratory test to determine the liquid limit of a silty clay soil, the results obtained are as below:

Where; W1 = weight of container , W2 = weight of container + wet soil and W3 = weight of container + oven-dried soil

Find the liquid limit. If the plastic limit and the natural water content of the soil are 22% and 35% respectively, calculate the plasticity and liquidity index of the sample.c) Classify the soil using plasticity chart.

TestW1 (g)W2(g)W3(g)Depth of cone penetration (mm)111.6221.2619.08 15.5210.8719.5017.24 20.0311.2121.2018.29 24.0410.4619.6216.74 27.5


Prepared by: Jodin MakindaAnswer


Chart1

15.5

20

24

27.5

Sheet1

29.2215.5

35.4720

4124

45.8527.5

10.4619.6216.74

45.8598726115

Sheet1

Sheet2

Sheet3

*

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Soil Classification