Thursday, September 3, 2020

Shrinkage Limit

Determination of Shrinkage limit of a soil sample.

 SHRINKAGE LIMIT

Shrinkage limit title image

The Atterberg limit are Liquid limit, Plastic limit and Shrinkage limit. The Liquid limit and the Plastic limit are described earlier. Now to determination of Atterberg Limit, Shrinkage limit need to calculate. The complete guide describe about How to find out Shrinkage limit and How to calculate the shrinkage ratio for a given soil sample.

Soil changes volume  with change in water content.  Volume changes may not be equal with the water content.

The Shrinkage limit test may be performed on a soil to Obtain - 

  • The volumetric indication of how much change in water content can occur before any amount of  volume changes occurs.
  • A quantitative indication of change in volume.

The shrinkage limit of soil sample is very important in areas where soils go through large volume changes when going through wet and dry cycles (as in case of earth dams)


MATERIAL & EQUIPMENTS :- 

  • Evaporating Dish. Porcelain, about 12cm diameter with flat bottom.
  • Spatula.
  • Circular Shrinkage Dish. 
  • Straight Edge. Steel, 15 cm in length.
  • Glass cup. About 50 mm diameter and 25 mm in height.
  • Glass plates. Two, each 75 X 75 mm2 one plate shall be of plain glass and the other shall   have prongs.
  • Sieves. 2mm and 475- micron IS sieves.
  • Oven-thermostatically controlled.
  • Graduate-Glass, having a capacity of 25 ml and graduated to 0.2 ml and 100 cc one mark   flask.
  • Balance-Sensitive to 0.01 g minimum.
  • Mercury. 
  • Wash bottle containing distilled water.


TEST PROCEDURE :-

Preparation of soil paste

  • Take about 100 gm of soil sample passing  through 475-micron I.S. sieve.   
  • Take about 30 gm the above soil sample and mixed  with distilled water and make a creamy paste in the evaporating dish and thoroughly .Use water content around the liquid limit.

Filling the shrinkage dish
  • Make a Coat to the shrinkage dish with a thin layer of Vaseline to prevent the soil sticking to the dish.
  • Fill the dish in three layers by wet soil with the help of spatula. Tap over the dish softly by hand on a firm base until the soil flows over the edges and ensure no apparent air bubbles exist. Repeat this process for 2nd and 3rd consecutive layers untill the dish is completely filled with the wet soil. Trim and smooth the face of soil by grooving tools.
  • Weight and record the dish.
  • Air- dry the wet soil in room temperature for 6 to 8 hrs, until the colour of the pat changes from dark to light. Then oven-dry it to constant weight at 1050C to 1100C say about 12 to 16 hrs.
  • Extract the dried container of the soil from oven. Cool it in a desiccator. Measure the weight of the dish with dry sample.
  • Calculate and record the weight of the empty dish.
  • Calculate the volume of shrinkage dish which is eventually equal to volume of the wet soil as follows. Place the shrinkage dish in an evaporating dish. Now add sufficient amount of mercury to the dish till  it overflows. Press it smoothly 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 out the volume of the shrinkage dish. That is the volume of the wet soil pat, Record the data in Tabular form.


Volume of the Dry Soil Pat

  • 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.
  • Pour the overflowing mercury to a large glass cup. The excess mercury are removed by covering the cup with glass plate with prongs and pressing it. Should be taken care that no air bubbles are entrapped. Carefully clean the outer side of the glass cup to remove the adhering mercury and place it in a clean larger dish.
  • Put down the dry soil pat on the mercury filled glass cup. Now the soil pat floats, submerge the pat with the pronged glass plate which is again made blush with top of the cup. The mercury overflows into the larger plate. Place the mercury that is displaced by the soil pat into the measuring jar then finally find out the volume of the soil pat.


OBSERVATION :-


Shrinkage limit table image


CALCULATION -


Shrinkage limit formula image




RESULT - 

The Shrinkage limit of the soil specimen =  










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