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Consistency limits and its determination

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Consistency limits and its determination

  1. 1. Defination Soil consistency is the strength with which soil materials are held together or the resistance of soils to deformation and rupture. The water contents at which the soil changes from one state to the other are known as consistency limit. The consistency of a fine grained soil is the physical state in which it exists.
  2. 2. Historical background Swedish agriculture engineer ATTERBERG was the one who mentioned that a fine grained soil can exist in four states: liquid plastic semi-solid solid So consistency limits are also known Atterberg’s limits.
  3. 3. Determination of consistency limitsConsistency limit can be determined by following test: Liquid limit test Shrinkage limit test Plastic limit test
  4. 4. Liquid limit testOBJECTIVEi. Prepare soil specimen as per specification.ii. Find the relationship between water content and number of blows.iii. Draw flow curve.iv. Find out liquid limit.
  5. 5. Liquid limit test NEED AND SCOPE Liquid limit is significant to know the stress history and general properties of the soil met with construction. From the results of liquid limit the compression index may be estimated. The compression index value will help us in settlement analysis. If the natural moisture content of soil is closer to liquid limit, the soil can be considered as soft if the moisture content is lesser than liquids limit, the soil can be considered as soft if the moisture content is lesser than liquid limit. The soil is brittle and stiffer.
  6. 6. Liquid limit test PROCEDURE1. About 120 gm of air-dried soil from thoroughly mixed portion of material passing 425 micron I.S sieve is to be obtained.2. Distilled water is mixed to the soil thus obtained in a mixing disc to form uniform paste. The paste shall have a consistency that would require 30 to 35 drops of cup to cause closer of standard groove for sufficient length.3. A portion of the paste is placed in the cup of LIQUID LIMIT device and spread into portion with few strokes of spatula.
  7. 7. Liquid limit test4. Trim it to a depth of 1cm at the point of maximum thickness and return excess of soil to the dish.5. The soil in the cup shall be divided by the firm strokes of the grooving tool along the diameter through the centre line of the follower so that clean sharp groove of proper dimension is formed.6. Lift and drop the cup by turning crank at the rate of two revolutions per second until the two halves of soil cake come in contact with each other for a length of about 1 cm by flow only.
  8. 8. Liquid limit test7. The number of blows required to cause the groove close for about 1 cm shall be recorded.8. A representative portion of soil is taken from the cup for water content determination.9. Repeat the test with different moisture contents at least three more times for blows between 10 and 40.
  9. 9. Liquid limit test Determination 1 2 3 4 Number OBSERVATION Container S number Details of the Weight of container sample:....... Weight of Natural moisture container + wet content:........ soil Weight of container + dry Room soil temperature:....... Weight of water Weight of dry ....... soil Moisture content (%) No. of blows
  10. 10. Liquid limit test COMPUTATION / CALCULATION Draw a graph showing the relationship between water content (on y-axis) and number of blows (on x-axis) on semi-log graph. The curve obtained is called flow curve. The moisture content corresponding to 25 drops (blows) as read from the represents liquid limit. It is usually expressed to the nearest whole number.
  11. 11. Liquid limit test INTERPRETATION AND RECORDINGa. Flow index If = (W2-W1)/(logN1/N2) = slope of the flow curve.b. Plasticity Index = wl-wpc. Toughness Index = Ip/If
  12. 12.  OBJECTIVE To determine the shrinkage limit and calculate the shrinkage ratio for the given soil.
  13. 13.  THEORY As the soil loses moisture, either in its natural environment, or by artificial means in laboratory it changes from liquid state to plastic state, from plastic state to semi-solid state and then to solid state. Volume changes also occur with changes in water content. But there is particular limit at which any moisture change does not cause soil any volume change.
  14. 14.  NEED AND SCOPE Soils which undergo large volume changes with change in water content may be troublesome. Volume changes may not and usually will not be equal. A shrinkage limit test should be performed on a soil. 1. To obtain a quantitative indication of how much change in moisture can occur before any appreciable volume changes occurs 2. To obtain an indication of change in volume. The shrinkage limit is useful in areas where soils undergo large volume changes when going through wet and dry cycles (as in case of earth dams)
  15. 15.  NEED AND SCOPE Soil is used for making bricks , tiles , soil cement blocks in addition to its use as foundation for structures.