Bearing capacity for different types of soil

Determination of specific gravity of soil

OBJECTIVE :

 To determine the specific gravity of soil fraction passing 4.75 mm I.S sieve by Pycnometer.

 

 DEFINITION

 Specific gravity G is defined as the ratio of the weight of an equal volume of distilled water at
that temperature both weights taken in air.

 APPARATUS USED
1. Pycnometer
2. Balance to weigh the materials (accuracy 10gm).
3. Wash bottle with distilled water.
4. Alcohol and ether.

PROCEDURE

➤ Clean and dry the pycnometer
➤ Wash the pycnometer with water and allow it to drain.
➤Wash it with alcohol and drain it to remove water.
➤ Wash it with ether, to remove alcohol and drain ether.
➤ Weigh the pycnometer (W1)
➤Take about 200 gm of oven-dried soil sample which is cooled in a desiccator. Transfer it to
the pycnometer. Find the weight of the pycnometer and soil (W2).
➤ Put 10ml of distilled water in the pycnometer to allow the soil to soak completely. Leave it
for about 2 hours.
➤ Again fill the pycnometer completely with distilled water put the stopper and keep the
pycnometer under constant temperature water baths (Tx0).
➤ Take the pycnometer outside and wipe it clean and dry it. Now determine the weight of the
pycnometer and the contents (W3).
➤ Now empty the pycnometer and thoroughly clean it. Fill the pycnometer with only distilled
water and weigh it. Let it be W4 at temperature (Tx0 C).

 OBSERVATIONS :

 Average specific gravity at Tx 0 C

 CALCULATIONS

 

specific gravity of soil = (Density of water at 27॰c)/Weight of water of equal volume.

 Repeat the same process for 2 to 3 times, to take the average reading of it.

 RESULT
Specific Gravity of given soil = (.........)

     

Determination of plastic limit of soil in the lab

Plastic limit test:-

This test is done to determine the plastic limit of soil as per IS: 2720 (Part 5) – 1985.The plastic limit of fine-grainedsoil is the water content of the soil below which it ceases to be plastic. It begins to crumble when rolled into threadsof 3mm dia.

 The apparatus used:

        i.            Porcelain evaporating dish about 120mm dia.

      ii.            Spatula

    iii.            Container to determine moisture content

    iv.            Balance, with an accuracy of 0.01g

      v.            Oven

    vi.            Ground glass plate – 20cm x 15cm

  vii.            Rod – 3mm dia. and about 10cm long

Preparation of sample:

Take out 30g of air-dried soil from a thoroughly mixed sample of the soil passing through 425µm IS Sieve. Mix thesoil with distilled water in an evaporating dish and leave the soil mass for 24hrs.Procedure to determine The Plastic Limit of Soil.

Procedure 

        i.         Take about 8g of the soil and roll it with fingers on a glass plate. The rate of rolling should be              between 80 to 90strokes per minute to form a 3mm dia.

      ii.         If the dia. of the threads can be reduced to less than 3mm, without any cracks appearing, it means that the watercontent is more than its plastic limit. Knead the soil to reduce the water content and roll it into a thread again.

    iii.          Repeat the process of alternate rolling and kneading until the thread crumbles.

    iv.        Collect and keep the pieces of crumbled soil thread in the container used to determine the moisture   content.

      v.           Repeat the process at least twice more with fresh samples of plastic soil each time.

Reporting of result

The plastic limit should be determined for at least three portions of the soil passing through 425µm IS Sieve. Theaverage water content to the nearest whole number should be reported.