To determine moisture content and dry density relationship using heavy compaction or modified compaction method as per IS-2720-Part-8.
• Metal mould (volume = 1000 cm3)
• Balance (capacity = 10 kg, least count = 1g)
• Oven (105 to 1100C)
• Sieve (19 mm)
• Metal rammer (weight = 4.9 kg)
Dry the soil sample by exposing it to air or sun light.
Sieve the air dried soil through 19 mm sieve.
Add suitable amount of water with the soil and mix it thoroughly. For sandy and gravelly soil add 3% to 5% of water. For cohesive soil the amount of water to be added should be 12% to 16%below the plastic limit.
Weigh the mould with base plate attached to the nearest 1g. Record this weight as ‘W1’.
Attach the extension collar with the mould.
Compact the moist soil into the mould in five layers of approximately equal mass, each layer being given 25 blows, with the help of 4.9 kg rammer, dropped from a height of 450 mm above the soil. The blows must be distributed uniformly over the surface of each layer.
After completion of the compaction operation, remove the extension collar and level carefully the top of the mould by means of straightedge.
Weigh the mould with the compacted soil to the nearest 1 g. Record this weight as ‘W2’.
After weighing remove the compacted soil from the mould and place it on the mixing tray. Determine the water content of a representative sample of the specimen. Record the moisture content as ‘M’.
Broken up the remainder of the specimen and repeat step 5 to step 9 by adding suitable increment of water to the soil. For sandy and gravelly soils the increment in general is 1% to 2%. For cohesive soils the increment in general is 2% to 4%.
The total no. of determinations made shall be at least five, and the moisture contents should be such that the optimum moisture content, at which the maximum dry density occurs, is within that range.
Bulk density, γb in g/cm3 of each compacted specimen is calculated from the following equation.
γb = (W2-W1)/Vm
W1 = Weight in g of mould + base plate
W2 = Weight in g of mould + base plate + soil
Vm = Volume of mould i.e. 1000 cm3.
Dry density, γd in g/cm3 of each compacted specimen is calculated from the following equation.
γd = 100 γb/(100+M)
γb = Bulkdensity of soil in g/cm3.
M = Moisture content of soil
The dry densities, γd , obtained in a series of determinations is plotted against the corresponding moisture content ‘M’. A smooth curve is then drawn through the resulting points and the position of the maximum on this curve is determined, which is called maximum dry density (M.D.D). And the corresponding moisture content is called optimum moisture content (O.M.C.).