UNIT WEIGHT OF SOIL :- Unit weight of soil can be determined using following methods.
Core-Cutter Method
- It is field method.
- Core cutter of known volume 1000 CC is pushed into the ground and then core containing soil is taken out from the ground.
- Weight of with soil sample (W2) and empty core (W1) is measured. Hence bulk unit is given as
γb = Weight of soil / Volume
= W2 – W1 / V
- The measuring water content of given sample, dry unit weight can be Calculated as
γd = γb / 1 + W
- This method generally not suitable for gravels, sand and dry soil.
- This is generally using for soft silt and clay.
Water Displacement Method
- This method is generally used for choesive soil that are highly sticky in nature.
- In this method sample of soil is trimmed into more or less uniform shape and weighed ( W1).
- Sample is then coated with paraffin wax and is again weighd (W2), Coating prevent entry of water into sample.
- The coated specimen of soil is immersed slowly in a container, that is completely filled with water and volume of water displaced by coated specimen is Vw.
Volume of paraffin wax = W2 – W1 / γpw
= W2 – W1 / Gpw γw
Vw = Volume of soil + Volume of paraffin wax
Volume of soil = Vw – Volume of paraffin max
= Vw – W2 – W1 / γpw
Unit weight of soil = Weight of soil / Volume of soil
= W1 / Vw – { W2 – W1 /γpw }
Submerged Density Method
- This method is used for cohesive soils which are very highly sticky in nature.
- In this method submerged mass of coated specimen W3 is noted to find volume of water displaced by soil + Paraffin wax.
Weight of paraffin wax = W2 – W1
Volume of paraffin wax = W2 – W1 / γpw
= W2 – W1 / Gpw γpw
Submerged weight of coated specimen = W2 – Fa
Fb = Force of buoyancy = Vwδw
W3 = W2 – Fb
= W2 – Vwδw
Vw = Volume of soil + Volume of paraffin wax
= W2 – W3 / γw
Volume of soil = Vw – Vpw
= W2 – W3 / γw – W2 – W1 / γpw
Unit weight of soil
= W1 / (W2 – W3 / γw – W2 – W1 / γpw )
Sand Replacement Method
- It is field method.
- A small pit is excavated and the excavated soil sample is weighed.
- A calibrated cylinder containing sand is placed over the excavated pit and is filled with sand.
- Volume of the pit is obtained from the calibrated cylinder.
- The bulk unit weight is calculated as
γb = Weight / Volume
- It is suitable for gravel , sand and dry soil.
