Standard Proctor Test
R. R. Proctor showed that:
Proctor proposed tests to determine relationship between moisture content, dry density or void ratio of a compacted soil in a standard manner and to determine the OMC for the soil.
Standard Proctor Test covers the determination of the relationship between the moisture content and density of soils compacted in a mould of a given size with a 2.5 kg rammer dropped from a height of 305 mm.
R. R. Proctor showed that:
- There exists a definite relationship between the soil moisture content and the degree of dry density to which a soil may be compacted.
- That for a specific amount of compaction energy applied on the soil, there is one moisture content termed Optimum Moisture Content (OMC) or Optimum Water Content (OWC) at which a particular soil attains maximum dry density.
Proctor proposed tests to determine relationship between moisture content, dry density or void ratio of a compacted soil in a standard manner and to determine the OMC for the soil.
Standard Proctor Test covers the determination of the relationship between the moisture content and density of soils compacted in a mould of a given size with a 2.5 kg rammer dropped from a height of 305 mm.
- Internal diameter of mould = 100 mm
Mould has detachable collar and base plate assembly.
2. Mechanically operated rammer has a face diameter of 50 mm and a free falling weight of 2.5 kg.
3. The height of drop is 305 mm.
Procedure for Standard Proctor Test
- Approximately 5 kg of soil passing through 4.75 mm sieve is thoroughly mixed with known water content. For fine soil, 8-10% of water and for coarse soil, 4-5% of water is added.
- Weight of the mould without base plate and collar is taken. The collar and base plate were fixed.
- In the mould, the weighed soil is compacted in 3 layers giving 25 blows per layer with the 2.5 kg rammer.
- Mould and soil, after making soil flush with the mould edges, are weighed.
- The sample is removed from the mould and sliced vertically to obtain a small sample for water content determination.
- The remainder of the material is thoroughly broken up.
- The water content is increased by one or two percentage and the above procedures are repeated for each increment.
- This series of determination is continued until there is a decrease in the wet unit weight of the compacted soil.
Standard Proctor Test - Calculation
Compaction Curve
Principles of Compaction and Moisture-Density Relations
If more than 20% soil is retained on 4.75 mm sieve,the soil is compacted in a layer mould having 150 mm diameter. Each layer is compacted giving 56 number of blows.
Weight of rammer = 2.6 kg (2.59kg)
- When moisture content is less than OMC, soil is stiff and difficult to compress; low density and high air voids are obtained.
- Increase in moisture content lubricates and softens soil (softening of clay bonds), reduces surface tension forces within the soil and makes it more workable; higher densities and low air voids obtained.
- As the air content becomes less, the water and air in combination tend to keep the particles apart and prevent any appreciable decrease in the air content. The total air voids, however continue to increase with moisture content and hence the dry density of soil falls. (density of water << density of soil)
- To the right of OMC the curve approaches saturation line but never reaches; it is never possible to expel all the entrapped air.
If more than 20% soil is retained on 4.75 mm sieve,the soil is compacted in a layer mould having 150 mm diameter. Each layer is compacted giving 56 number of blows.
Weight of rammer = 2.6 kg (2.59kg)
AASHTO or Modified Proctor Test
In Modified Proctor Test, compactive energy is about 4.56 times greater than in Standard Proctor Test.
- Standard Proctor Test is not sufficient for airways and highways where heavier compaction is required.
- US Army Corps of Engineers developed Modified Proctor Test which used greater levels of compaction and produced higher densities.
- Modified Proctor Test was alter adopted by AASHTO and ASTM.
- Internal Diameter of Mould = 100 mm, Height of Mould = 127.3 mm
- Mould has detachable collar and base plate assembly as in the case of Standard Proctor Test.
- Mechanically operated rammer has a face diameter of 50 mm and a free falling weight of 4.89 kg. The height of drop is 450 mm.
- In the mould, the soil is compacted in 5 layers giving 25 blows per layer with the 4.89 kg rammer.
In Modified Proctor Test, compactive energy is about 4.56 times greater than in Standard Proctor Test.
Differences in Lab and Field Conditions:
So lab density differs from field density.
- Quantity of Soil
- Manually compacted in Lab.
- Soil compacted in confined area in Lab.
- Lab has controlled conditions.
So lab density differs from field density.
Importance of Proctor Test
- It gives the density that must be achieved in the field.
- Provides the moisture range that allows for minimum compactive effort to achieve density.
- Provides data on the behaviour of the material in relation to various moisture contents.
- It is not possible to determine whether a density test passes or fails without it.