Shrinkage limit test of soil IS 2720-Part 6

Method of shrinkage limit test of soil

Shrinkage limit test of soil, The shrinkage limit of soil is the water content of the soil when the soil is just saturated. The volume of the soil does not decrease when the water content is reduced. 

Test standard: IS 2720-Part 6:1972, Reaffirmed 2011
 
Test Apparatus:
  • Evaporating dish,
  • Spatula
  • Shrinkage dish
  • Straight edge
  • Glass cup
  • Glass plates
  • Hot air oven
  • IS Sieve 425 microns
  • Balance of accuracy 0.1 gm
  • Mercury 
  • Desiccator. 

Preparation of soil sample:

Take about 30 gm of soil sample sieved through IS Sieve 425 microns in an evaporating dish and thoroughly mix with distilled water in an amount sufficient to fill the soil voids completely and to make the soil pasty enough to be readily worked into the shrinkage dish without entrapping air bubbles.

Test Procedure:

  • Determine the weight of the clean empty shrinkage dish and record. 
  • Determine the capacity of the shrinkage dish in cubic centimeters, which is also the volume of the wet soil pat, by filling the shrinkage dish to overflowing with mercury, removing the excess by pressing the plain glass plate firmly over the top of the shrinkage dish in such a way that plate is flush with the top of the dish and no air is entrapped.
  • Weighing the mercury held in the shrinkage dish to an accuracy of 0.1gms and dividing this weight by unit weight of the mercury to obtain the volume. 
  • Record this volume as volume of the wet soil pat (V) .
  • Coat the inside of the shrinkage dish with heavy grease to prevent the adhesion of soil with the dish.
  • Place in the centre of the shrinkage dish an amount of soil paste equal to one-third the volume of the shrinkage dish and allow the paste to flow to the edges by tapping the shrinkage dish on a firm surface cushioned by several layers of rubber sheet or similar material. 
  • Add an amount of soil paste approximately equal to the first portion and tap the shrinkage dish as before until the paste is thoroughly compacted and all air voids has been brought to the surface. Add more soil paste and continue the tapping until the shrinkage dish is completely filled and excess paste stand out at its edge. Then strike off the excess soil paste with a straight edge and wipe off all soil adhering to the outside of the shrinkage dish. 
  • Weigh immediately the shrinkage dish as filled and record the weight as weight of the shrinkage dish and weight of the wet soil pat. Allow the soil pat to dry in air until the colour of the pat turns from dark to light.
  • Then oven dry the pat to in a shrinkage dish to constant weight at 105-110oC, cool in a desiccator and weigh immediately after removal from the desiccator. Record this weight as weight of the shrinkage dish and dry pat.
  • Determine the volume of the dry soil pat by removing the pat from the shrinkage dish and immersing it in a glass cup full of mercury to overflowing and removing the excess mercury by pressing the glass plate with three prongs, firmly over the top of the cup, collecting the excess mercury in a suitable container.
  • Wipe off any mercury adhering to the outside of the cup. Place the cup filled thus with mercury in an evaporating dish taking care not to spill any mercury from the cup and place the oven dried soil pat on the surface of the mercury in the cup.
  • Then carefully force the pat under the mercury by means of the glass plate with the same prongs and press the plate firmly over the top of the cup, the displaced mercury being collected in the evaporating dish without spilling out of it.
  • Weigh the mercury so displaced by the dry soil pat to an accuracy of 0.1gms and determine the volume by dividing this weight by unit weight of the mercury.
  • Record this volume as volume of the oven dry pat, Vo.

Moisture content of the wet soil pat (w)= {(W-Wo)/Wo} x100

W = weight of the wet soil pat obtained by subtracting the weight of the shrinkage dish from the weight of the dish and wet pat.

Wo = weight of the dry soil pat obtained by subtracting the weight of the shrinkage dish from the weight of the dish and dry pat.

Calculation of Shrinkage limit (Ws)

 = w- {(V-Vo)/Wo} x100 

Ws= shrinkage limit (%)
w = moisture content of the wet soil pat
V= volume of the wet soil in ml
Vo = volume of the dry soil pat in ml
Wo = weight of the oven dry soil pat in gms
 
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Rajkumar ghagre

Founder & Admin of civilengineeringsolution.com, I am a civil engineer working as a Assistant Engineer (QA/QC).

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