Objective
Determination of water content and dry density relation of soil using light compaction.
Apparatus
• Cylindrical mould of 100mm diameter & accessories [volume = 1000 c.c.]
• Rammer [2.6 kg]
• Balance [(a) 10kg capacity & 1g accuracy (b) 200gm capacity & 0.01gm accuracy for moisture content calculation]
• Sieves [19mm & 4.75mm IS sieves]
• Mixing tray
• Trowel/spatula/straight edge
• Graduated cylinder [500 ml capacity]
• Metal container
• Oven [105°C and 110°C capacity] etc.
Preparation of test specimen
Obtain a sufficient quantity (10 kg) of air-dried soil and pulverize it. Take about 5 kg of soil passing through 19mm sieve in a mixing tray.
Procedure
1. 5 Kg. of soil is taken and the water is added to it to bring its moisture content to about 4- 6 % in coarse grained soils and 8-10% in case of fine grained soils with the help of graduated cylinder
2. The mould with base plate attached is weighed to the nearest 1 gm (M1). The extension collar is to be attached with the mould.
3. Then the moist soil in the mould is compacted in three equal layers, each layer being given 25 blows from the 2.6 Kg rammer dropped from a height of 310 mm. above the soil.
4. The extension is removed and the compacted soil is levelled off carefully to the top of the mould by means of a straight edge.
5. Then the mould and soil is weighed to the nearest 1 gm. (M2).
6. The soil is removed from the mould and a representative soil sample is obtained water content determination.
7. Steps 3 to 6 are repeated after adding suitable amount of water to the soil in an increasing order. For sandy and gravelly soil increment of adding moisture should be of 1-2% and for clayey soil 2-4%.
Result
Bulk density, gm in g/cm3 at each compacted specimen is calculated from the equation.
Bulk density ᵞm = (M2-M1) / Vm
where Vm = volume of mould in cm3 =1000 c.c.
The dry density, ᵞd, in g/c.c., is calculated from the equation.
ᵞd = (100 ᵞm )/ (100+w)
where w = moisture content of soil in percent.
The dry densities, ᵞd obtained in a series of determinations are plotted against the corresponding moisture content. A smooth curve or by best fitted curve is then drawn through the resulting points and the position of the maximum on this curve is determined.
Report
The maximum dry density in gm/c.c. is to be reported to the nearest 0.01 and the optimum moisture content is to be reported to the nearest 0.5.
