DETERMINATION OF CONSISTENCY LIMITS

LIQUID LIMIT TEST

OBJECTIVE

1.Prepare soil specimen as per specification.
2.Find the relationship between water content and number of blows.
3.Draw flow curve.
4.Find out liquid limit.

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.

 THEORY

The liquid limit is the moisture content at which the groove, formed by a standard tool into the sample of soil taken in the standard cup, closes for 10 mm on being given 25 blows in a standard manner. At this limit the soil possess low shear strength.

 APPARATUS REQUIRED

 1. Balance   2. Liquid limit device  (Casagrende’s)   3. Grooving tool   4. Mixing dishes 

 5. Spatula   6. Electrical Oven  

PROCEDURE

1. 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.

4. 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.

7. 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.  

OBSERVATIONS

Details of the sample:.......

Natural moisture content:........                Room temperature:..............

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.

 INTERPRETATION AND RECORDING 

Flow index I_f = (W₂-W₁)/(logN₁/N₂) = slope of the flow curve.

Plasticity Index = w_l-w_p =

Toughness Index = I_p/I_f =

PLASTIC LIMIT TEST

NEED AND SCOPE  

Soil is used for making bricks , tiles , soil cement blocks in addition to its use as foundation for structures.

APPARATUS REQUIRED

1.Porcelain dish.
2.Glass plate for rolling the specimen.
3.Air tight containers to determine the moisture content.
4.Balance of capacity 200gm and sensitive to 0.01gm
5.Oven thermostatically controlled with interior of non-corroding material to maintain the temperature around 105⁰ and 110⁰C.

PROCEDURE

1. Take about 20gm of thoroughly mixed portion of the material passing through 425 micron  I.S.  sieve obtained in accordance with I.S. 2720 (part 1).

2. Mix it thoroughly with distilled water in the evaporating dish till the soil mass becomes   plastic enough to be easily molded with fingers.

3. Allow it to season for sufficient time  (for  24 hrs) to allow water to permeate throughout the soil mass

4. Take about 10gms of this plastic soil mass and roll it between fingers and glass plate with  just sufficient pressure to roll the mass into a threaded of uniform diameter throughout its   length. The rate of rolling shall be between 60 and 90 strokes per minute.

5. Continue rolling till you get a threaded of 3 mm diameter.

6. Kneed the soil together to a uniform mass and re-roll.

7. Continue the process until the thread crumbles when the diameter is 3 mm.

8. Collect the pieces of the crumbled thread in air tight container for moisture content  determination.

9. Repeat the test to atleast 3 times and take the average of the results calculated to the nearest   whole number.

OBSERVATION AND REPORTING

Compare the diameter of thread at intervals with the rod. When the diameter reduces to 3 mm, note the surface of the thread for cracks.

PRESENTATION OF DATA

Average Plastic Limit=...............

Plasticity Index(Ip) = (LL - PL)=............        Toughness Index =Ip/I_F

SHRINKAGE LIMIT TEST

OBJECTIVE

To determine the shrinkage limit and calculate the shrinkage ratio for the given soil. 

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. 

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)

 APPARATUS

1.  Evaporating Dish. Porcelain, about 12cm diameter with flat bottom.

2.  Spatula

3.  Shrinkage Dish. Circular, porcelain or non-corroding metal dish (3 nos) having a flat   bottom and 45 mm in diameter and 15 mm in height internally.

4.  Straight Edge. Steel, 15 cmm in length.

5.  Glass cup. 50 to 55 mm in diameter and 25 mm in height , the top rim of which is ground   smooth and level.

6.  Glass plates. Two, each 75 ´ 75 mm one plate shall be of plain glass and the other shall   have prongs.

7.  Sieves. 2mm and 425- micron IS sieves.

8.  Oven-thermostatically controlled.

9.  Graduate-Glass, having a capacity of 25 ml and graduated to 0.2 ml and 100 cc one –mark   flask.

10.Balance-Sensitive to 0.01 g minimum.

11.Mercury. Clean, sufficient to fill the glass cup to over flowing.

12.Wash bottle containing distilled water.

PROCEDURE

 Preparation of soil paste

1. Take about 100 gm of soil sample from a thoroughly mixed portion of the material passing  through 425-micron I.S. sieve.

2. Place about 30 gm the above soil sample in the evaporating dish and thoroughly mixed  with distilled water and make a creamy paste.

Use water content some where around the liquid limit.

 Filling the shrinkage dish

3. Coat the inside of the shrinkage dish with a thin layer of Vaseline to prevent the soil sticking to the dish.

4. Fill the dish in three layers by placing approximately 1/3 rd of the amount of wet soil with the help of spatula. Tap the dish gently on a firm base until the soil flows over the edges and no apparent air bubbles exist. Repeat this process for 2nd and 3rd layers also till the dish is completely filled with the wet soil. Strike off the excess soil and make the top of the dish smooth. Wipe off all the soil adhering to the outside of the dish.

5. Weigh immediately, the dish with wet soil and record the weight.

6. Air- dry the wet soil cake for 6 to 8hrs, until the colour of the pat turns from dark to light. Then oven-dry the to constant weight at 105⁰C to 110⁰C say about 12 to 16 hrs.

7. Remove the dried disk of the soil from oven. Cool it in a desiccator. Then obtain the weight of the dish with dry sample.

8. Determine the weight of the empty dish and record.

9. Determine the volume of shrinkage dish which is evidently equal to volume of the wet soil as follows. Place the shrinkage dish in an evaporating dish and fill the dish with mercury  till  it overflows slightly. Press it with plain glass plate firmly on its top to remove excess mercury. Pour the mercury from the shrinkage dish into a measuring jar and find the volume of the shrinkage dish directly. Record this volume as the volume of the wet soil pat.

 Volume of the Dry Soil Pat

10. Determine the volume of  dry soil pat by removing the pat from the shrinkage dish and immersing it in the glass cup full of mercury in the following manner.

 Place the glass cup in a larger one and fill the glass cup to overflowing with mercury. Remove the excess mercury by covering the cup with glass plate with prongs and pressing it. See that no air bubbles are entrapped. Wipe out the outside of the glass cup to remove the adhering mercury. Then, place it in another larger dish, which is, clean and empty carefully.

 Place the dry soil pat on the mercury. It floats submerge it with the pronged glass plate which is again made flush with top of the cup. The mercury spills over into the larger plate. Pour the mercury that is displayed by the soil pat into the measuring jar and find the volume of the soil pat  directly.

CALCULATION

CAUTION

Do not touch the mercury with gold rings.

  TABULATION AND RESULTS  

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