Compaction test of soil is carried out using Proctor’s test to understand compaction characteristics of different soils with change in moisture content. Compaction of soil is the optimal moisture content at which a given soil type becomes most dense and achieve its maximum dry density by removal of air voids.
Proctor Soil Compaction Test
Compaction is the process of densification of soil by reducing air voids. The degree of compaction of a given soil is measured in terms of its dry density. The dry density is maximum at the optimum water content. A curve is drawn between the water content and the dry density to obtain the maximum dry density and the optimum water content.
Dry density of soil:
Where M = total mass of the soil, V= volume of soil, w= water content.
Equipments for Proctor’s Test for Compaction of Soil
- Compaction mould, capacity 1000ml.
- Rammer, mass 2.6 kg
- Detachable base plate
- Collar, 60mm high
- IS sieve, 4.75 mm
- Weighing balance, accuracy 1g
- Large mixing pan
- Straight edge
- Graduated jar
- Mixing tools, spoons, trowels, etc.
Proctor Soil Compaction Test Procedure
- Take about 20kg of air-dried soil. Sieve it through 20mm and 4.7mm sieve.
- Calculate the percentage retained on 20mm sieve and 4.75mm sieve, and the percentage passing 4.75mm sieve.
- If the percentage retained on 4.75mm sieve is greater than 20, use the large mould of 150mm diameter. If it is less than 20%, the standard mould of 100mm diameter can be used. The following procedure is for the standard mould.
- Mix the soil retained on 4.75mm sieve and that passing 4.75mm sieve in proportions determined in step (2) to obtain about 16 to 18 kg of soil specimen.
- Clean and dry the mould and the base plate. Grease them lightly.
- Weigh the mould with the base plate to the nearest 1 gram.
- Take about 16 – 18 kg of soil specimen. Add water to it to bring the water content to about 4% if the soil is sandy and to about 8% if the soil is clayey.
- Keep the soil in an air-tight container for about 18 to 20 hours for maturing. Mix the soil thoroughly. Divide the processed soil into 6 to 8 parts.
- Attach the collar to the mould. Place the mould on a solid base.
- Take about 2.5kg of the processed soil, and hence place it in the mould in 3 equal layers. Take about one-third the quantity first, and compact it by giving 25 blows of the rammer. The blows should be uniformly distributed over the surface of each layer.
- The top surface of the first layer be scratched with spatula before placing the second layer. The second layer should also be compacted by 25 blows of rammer. Likewise, place the third layer and compact it.
- The amount of the soil used should be just sufficient to fill the mould ad leaving about 5 mm above the top of the mould to be struck off when the collar is removed.
- Remove the collar and trim off the excess soil projecting above the mould using a straight edge.
- Clean the base plate and the mould from outside. Weigh it to the nearest gram.
- Remove the soil from the mould. The soil may also be ejected out.
- Take the soil samples for the water content determination from the top, middle and bottom portions. Determine the water content.
- Add about 3% of the water to a fresh portion of the processed soil, and repeat the steps 10 to 14.
Fig: Standard Proctor Test (Compaction Test)
Data Sheet for Compaction Test of Soil
Diameter of the mould =
Height of mould =
Volume of the mould, V=
Specific gravity of solids, G=
|Sl. No.||Observations and Calculations||Determination No.|
|1||Mass of empty mould with base plate|
|2||Mass of mould, compacted soil and base plate|
|3||Mass of compacted soil M = (2) – (1)|
|5||Water content, w|
|8||Dry density at 100% saturation (theoretical)
|9||Degree of saturation|
Plot a curve between w as abscissa and as ordinate.
Fig: Soil Compaction Curve
Result of Proctor Soil Compaction Test
- Maximum dry density (from plot) =
- Optimum water content (from plot) =