HOW TO DETERMINE SPECIFIC GRAVITY OF SOIL?

Objective

For determination of specific gravity of soil solids by pycnometer method.

Equipment & Apparatus

  • Pycnometer
  • Sieve(4.75 mm)
  • Vacuum pump
  • Oven
  • Weighing balance
  • Glass rod

Preparation sample

After receiving the soil sample it is dried in oven at a temperature of 105 to 1150C for a period of 16 to 24 hours.

Procedure

  1. Dry the pycnometer and weigh it with its cap(W1)
  2. Take about 200 g to 300 g of oven dried soil passing through 4.75mm sieve into the pycnometer and weigh again(W2)
  3. Add water to cover the soil and screw on the cap.
  4. Shake the pycnometer well and connect it to the vacuum pump to remove entrapped air for about 10 to 20 minutes.
  5. After the air has been removed, fill the pycnometer with water and weigh it (W3).
  6. Clean the pycnometer by washing thoroughly.
  7. Fill the cleaned pycnometer completely with water up to its top with cap screw on.
  8. Weigh the pycnometer after drying it on the outside thoroughly (W4). 

Calculation

The Specific gravity of soil solids (Gs) is calculated using the following equation.

Soil specific gravity 1

 Where

W1=Empty weight of pycnometer

W2=Weight of pycnometer + oven dry soil

W3=Weight of pycnometer + oven dry soil + water

W4=Weight of pycnometer + water full

Report

The result of the specific gravity test is reported to the nearest two digits after decimal.

Safety & Precautions

  • Soil grains whose specific gravity is to be determined should be completely dry.
  • If on drying soil lumps are formed, they should be broken to its original size.
  • Inaccuracies in weighing and failure to completely eliminate the entrapped air are the main sources of error. Both should be avoided.

Reference Standard

IS : 2720 (Part 4) – 1985 – Method of test for soil (Part 4-Grain size analysis)

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