Determination atterberg's limit

SOIL MECHANICS LAB

1. DETERMINATION OF ATTERBERG LIMIT EXPERIMENT NO 6 SOIL MECHANICS LABORATORY CE PC 594

2. CONSISTENCY OF SOIL Consistency refers to degree of deformation which may be recorded in a soil due to change in water content Or It is a measure of relative case with which soil can be deformed.

3. CONSISTENCY OF SOIL Consistency is used only for fine grained soil (silt and clay) not for coarse grained soil (gravel and sand); as coarse soil can not be easily deformed by changing the water content. Consistency Flow with ease Firmness Strength Consistency  

4. PHASE OF SOIL There are four phases of soil. Liquid phase Plastic phase Semisolid phase Solid / Dry phase

5. CONSISTENCY OF SOIL Reducing Water Content Reduction in volume of soil Reduction in volume of soil Reducing Water Content No reduction in volume of soil Reducing Water Content Fully dry condition V L V P V Sr V d Saturated soil (S = 100%) Unsaturated soil (S<100%) V W1 V S V W2 V S V W3 V S V a V S

6. CONSISTENCY LIMIT OF SOIL The boundary between each state can be defined based on a change in the soil's behavior. The Atterberg limits can be used to distinguish between silt and clay, and it can distinguish between different types of silts and clays. These limits were created by Albert Atterberg, a Swedish chemist . They were later refined by Arthur Casagrande . There are THREE types of consistency limit of soil Liquid limit ( w L ) % Plastic Limit ( w P ) % Shrinkage Limit ( w Sr ) %

7. RELATION BETWEEN ATTERBERG LIMIT AND CORRESPONDING VOLUME V L V P V Sr = V d w L w P w Sr Water content (%)   Volume in cc   V S Here, w L = Liquid limit w P = Plastic Limit w Sr = Shrinkage limit V L = Volume at Liquid Limit V P = Volume at Plastic limit V Sr = Volume at Shrinkage limit V d = Dry volume of soil V S = Volume of soil solid Liquid phase Plastic phase Semi- Solid phase Solid phase

8. RELATION BETWEEN ATTERBERG LIMIT AND CORRESPONDING VOLUME V L V P V Sr = V d w L w P w Sr Water content (%)   Volume in cc   V S Note: 𝑆𝑙𝑜𝑝𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑢𝑟𝑣𝑒 𝑢𝑝 𝑡𝑜 𝑠ℎ𝑟𝑖𝑛𝑘𝑎𝑔𝑒 𝑙𝑖𝑚𝑖𝑡 = tan θ = = = = = constant As it is straight line.   Liquid phase Plastic phase Semi- Solid phase Solid phase θ

9. DEFINITION OF DIFFERENT CONSISTENCY LIMIT Liquid limit ( w L ) % - This is a water content at which soil comes in plastic stage from liquid stage. Or, It is minimum water content at which soil is in liquid stage or soil have tendency to flow. In liquid stage of consistency soil have negligible shear strength due to high content of water. As water content decreases, tendency of flow decreases means shear strength of soil increases At liquid limit, all the soils generally possesses negligible shear strength but that can be measured 2.7 kN/m 2 .

10. DEFINITION OF DIFFERENT CONSISTENCY LIMIT Liquid limit ( w L ) % - Types of soil Liquid limit Gravel Non- Plastic Sand Non- Plastic Silt 30-40% Clay (Alluvial) 40-150% Clay (Black soil) 400-500% Clay (Bentonite) 400-800% Note:- Soil having high L.L. possesses higher compressibility

11. DEFINITION OF DIFFERENT CONSISTENCY LIMIT Plastic Limit ( w P ) % - It is a water content at which soil passes from plastic stage to semi-solid stage. Or, It is minimum water content at which s oil is in plastic state of consistency. Types of soil Plastic limit Gravel Non- Plastic Sand Non- Plastic Silt 10-15% Clay (Alluvial) 15-100% Clay (Black soil) 200-250% Clay (Bentonite) 200-400%

12. DEFINITION OF DIFFERENT CONSISTENCY LIMIT Shrinkage Limit ( w Sr ) % - It is defined as the maximum water content after which if water is reduced volume of soil will not decreases. Or, It is the water content at which soil is at 100% degree of saturation for last time. Below shrinkage limit replacement of water by air takes place such that volume of voids is constant and volume of solid is also constant. It means when water content is decreased below shrinkage limit degree of saturation will be less than 100%.

13. CONSISTENCY INDEX OF SOIL There are SIX types of consistency index of soil Plasticity Index (I P ) % Consistency Index (I C ) % Liquidity Index (I L ) % Toughness Index ( I T ) Shrinkage Index ( I Sr ) % Flow Index (I f )

14. DEFINITION OF DIFFERENT CONSISTENCY INDEX Plasticity Index (I P ) % - It is a range of water content in which soil exhibits its plastic property. Organic soil possesses high liquid limit i.e. >50% but their plastic limit is also comparatively high. Hence its plasticity index is less approx. 10%. It means organic soil is highly compressive but less plastic.   Plasticity Plasticity Index Soil Type Non- Plastic 0% Sand Low Plastic 0-7% Silt Medium Plastic 7-17% Silty Clay Plastic >17% Clay

15. DEFINITION OF DIFFERENT CONSISTENCY INDEX Consistency Index (I C ) % - It is defined as the ratio of the difference between liquid limit and the natural water content to the plasticity index of a soil. ; w% = Natural water content of soil.   Consistency Description I C Liquid state Liquid state <0% Plastic State Very soft 0-25% Soft 25-50% Medium Soft 50-75% Stiff 75-100% Semi-solid state Very stiff to hard >100% Solid state Very hard >>100%

16. DEFINITION OF DIFFERENT CONSISTENCY INDEX Liquidity Index (I L ) % - It is the ratio of the difference between the natural water content and the plastic limit to the plasticity index. ; w% = Natural water content of soil .   Consistency Description I L Liquid state Liquid state >100% Plastic State Very soft 75-100% Soft 50-75% Medium Soft 25-50% Stiff 0-25% Semi-solid state Very stiff to hard <0% Solid state Very hard <<0%

17. DEFINITION OF DIFFERENT CONSISTENCY INDEX Toughness Index (I T ) % - It is defined as the ratio of plasticity index and flow index. ; = Flow index. Generally its value lies between 0-3 If for any soil its value less than 1, then soil is easily crushable at its plastic limit. It represents the strength of soil at plastic limit. NOTE :- Shear strength of soil at its plastic limit is approx. 100 times more than shear strength soil at its liquid limit.  

18. DEFINITION OF DIFFERENT CONSISTENCY INDEX Shrinkage Index ( I Sr ) % - It represents the range of water content in which soil is in semi- solid stage.  

19. DEFINITION OF DIFFERENT CONSISTENCY INDEX Flow Index (I f ) % - It is the slope of flow curve. Slope of the curve is assumed to be constant. It is the ratio of change in water content to change in number of blows in logarithmic scale. Flow curve is plotted between water content in Y axis and number of blows in logarithmic scale in X axis. For 25 number of blows, amount of water content obtained from floe curve is liquid limit ( w L %) Flow index represents rate of loss of shear strength of soil w.r.t change in water content More the I f , more will be the loss of shear strength.   w 1 w 2 w 3 N 1 N 2 N 3 Water Content (w%)   No. of Blows (N) log scale   w L 25

20. DEFINITION OF DIFFERENT CONSISTENCY INDEX Flow Index (I f ) % - NOTE: For ease in finding flow index water content should define corresponding to 10 & 100 number of blows. If rubber base is harder than standard base then flow index will be increases and flow curve will be steeper. w 10 w 100 10 Water Content (w%)   No. of Blows (N) log scale   w L 25 100   Water Content (w%)   Soft Base Standard Base Hard Base No. of Blows (N) log scale  

21. DETERMINATION OF LIQUID LIMIT EXPERIMENT NO 6 a GEOTECHNICAL ENGINEERING LABORATORY DIPLOMA

22. TESTS REQUIRED FOR LIQUID LIMIT DETERMINATION Casagrande Method One point Method Static Cone Penetrometer Method We will discuss only Casagrande method to determine liquid limit of fine grained soil.

23. Based on Casagrande , liquid limit may be defined as minimum water content at which a part of the soil cut by groove of standard size flow together to come closer by a distance of 0.5” (11-13 mm) under the impact of 25 number of blows. Apparatus required: Mechanical liquid limit device, grooving tool, porcelain evaporating dish, flat glass plate, spatula, palette knives, balance, oven wash bottle with distilled water and containers. LIQUID LIMIT TEST

24. LIQUID LIMIT TEST

25. LIQUID LIMIT TEST PROCEDURE: Take roughly 3/4 of the soil and place it into the porcelain dish. Assume that the soil was previously passed though a No. 40 sieve (425 µm), air-dried, and then pulverized. Thoroughly mix the soil with a small amount of distilled water until it appears as a smooth uniform paste. Cover the dish with cellophane to prevent moisture from escaping. Weigh four of the empty moisture cans with their lids, and record the respective weights and can numbers on the data sheet. Adjust the liquid limit apparatus by checking the height of drop of the cup. The point on the cup that comes in contact with the base should rise to a height of 10 mm. The block on the end of the grooving tool is 10 mm high and should be used as a gauge . Practice using the cup and determine the correct rate to rotate the crank so that the cup drops approximately two times per second.

26. LIQUID LIMIT TEST PROCEDURE: Place a portion of the previously mixed soil into the cup of the liquid limit apparatus at the point where the cup rests on the base. Squeeze the soil down to eliminate air pockets and spread it into the cup to a depth of about 10 mm at its deepest point. The soil pat should form an approximately horizontal surface. Use the grooving tool carefully cut a clean straight groove down the center of the cup. The tool should remain perpendicular to the surface of the cup as groove is being made. Use extreme care to prevent sliding the soil relative to the surface of the cup. STEP 4 STEP 5

27. LIQUID LIMIT TEST PROCEDURE: Make sure that the base of the apparatus below the cup and the underside of the cup is clean of soil. Turn the crank of the apparatus at a rate of approximately two drops per second and count the number of drops, N, it takes to make the two halves of the soil pat come into contact at the bottom of the groove along a distance of 13 mm (1/2 in .). If the number of drops exceeds 50, then go directly to step eight and do not record the number of drops, otherwise, record the number of drops on the data sheet . STEP 6 Take a sample, using the spatula, from edge to edge of the soil pat. The sample should include the soil on both sides of where the groove came into contact. Place the soil into a moisture can cover it. Immediately weigh the moisture can containing the soil, record its mass, remove the lid, and place the can into the oven. Leave the moisture can in the oven for at least 16 hours. Place the soil remaining in the cup into the porcelain dish. Clean and dry the cup on the apparatus and the grooving tool.

28. LIQUID LIMIT TEST PROCEDURE: Remix the entire soil specimen in the porcelain dish. Add a small amount of distilled water to increase the water content so that the number of drops required to close the groove decrease. Repeat steps six, seven, and eight for at least two additional trials producing successively lower numbers of drops to close the groove. One of the trials shall be for a closure requiring 25 to 35 drops, one for closure between 20 and 30 drops, and one trial for a closure requiring 15 to 25 drops. Determine the water content from each trial by using the same method used in the first laboratory. Remember to use the same balance for all weighing . Plot the graph between water content in Y axis and number of blows in X axis on log scale. From that curve, determine the liquid limit based on 25 number of blows.

29. LIQUID LIMIT TEST CALCULATION TABLE :-

30. LIQUID LIMIT TEST CALCULATION GRAPH :-

31. DETERMINATION OF PLASTIC LIMIT EXPERIMENT NO 6 b GEOTECHNICAL ENGINEERING LABORATORY DIPLOMA

32. Based on Casagrande , plastic limit may be defined as minimum water content at which if the soil is rolled into threads of 3 mm diameter then surface crack will just appear. Apparatus required: Porcelain evaporating dish, about 12 cm in diameter (or a flat glass plate, 10 mm thick and about 45 cm square), spatula, about 8 cm long and 2 cm wide (or palette knives, with the blade about 20 cm long and 3 cm wide, for use with flat glass plate for mixing soil and water), a ground-glass plate, about 20×15 cm, for a surface for rolling, balance, oven, containers, and a rod, 3 mm in diameter and about 10 cm long. PLASTIC LIMIT TEST Porcelain dish Moisture can Spatula Glass Plate 3 mm thread

33. PLASTIC LIMIT TEST PROCEDURE: Weigh the remaining empty moisture cans with their lids, and record the respective weights and can numbers on the data sheet. Take the remaining 1/4 of the original soil sample and add distilled water until the soil is at a consistency where it can be rolled without sticking to the hands. Form the soil into an ellipsoidal mass. Roll the mass between the palm or the fingers and the glass plate. Use sufficient pressure to roll the mass into a thread of uniform diameter by using about 90 strokes per minute. (A stroke is one complete motion of the hand forward and back to the starting position.) The thread shall be deformed so that its diameter reaches 3.2 mm (1/8 in.), taking no more than two minutes. STEP 3 STEP 4

34. PLASTIC LIMIT TEST PROCEDURE: When the diameter of the thread reaches the correct diameter, break the thread into several pieces. Knead and reform the pieces into ellipsoidal masses and re-roll them. Continue this alternate rolling, gathering together, kneading and re-rolling until the thread crumbles under the pressure required for rolling and can no longer be rolled into a 3.2 mm diameter thread. STEP 5 Gather the portions of the crumbled thread together and place the soil into a moisture can, then cover it. If the can does not contain at least 6 grams of soil, add soil to the can from the next trial (See Step 7). Immediately weigh the moisture can containing the soil, record its mass, remove the lid, and place the can into the oven. Leave the moisture can in the oven for at least 16 hours . Repeat steps three, four, and five at least two more times. Determine the water content from each trial by using the same method used in the first laboratory. Remember to use the same balance for all weighing.

35. PLASTIC LIMIT TEST CALCULATION TABLE :-

36. PLASTICITY CHART I p = 0.73 ( w L % -20%) 11 26 I p = 0.73 ( w L % -20 %) For, w L =26%, I p =0.73 (26-20) = 4.38

37. RESULT OF LIQUID LIMIT AND PLASTIC LIMIT TEST Liquid limit ( %) – 26% Plastic limit ( ) – 15% Plasticity Index ( ) = = 26-15 = 11% As L.L. is in between 30-40%, then soil is silty soil. As P.L. is in between 10-15%, then soil is silty soil As P.I. is in between 7-17%, then soil is medium plastic and mainly soil is silty clay. From plasticity chart, it is above A line. Hence, soil is CL i.e. low compressibility clay It can be concluded here that soil is low compressible silty clay.  

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