To determine the moisture-density relationship by Modified Proctor Test.

OBJECT: To determine the moisture-density relationship by Modified Proctor Test.

OBJECTIVE AND SCOPE

With the development of heavy rollers and their use in field compaction, the standard proctor test was modified to better represent field conditions. Modified Proctor Test is used to determine the compaction of different types of soil and the properties of soil with a change in moisture content and the relationship between dry density and moisture content.

STANDARDS

AASHTO T180-90

ASTM D1557-91

BIS1377:part 4; clause 4

APPARATUS

1. Proctor Mold
   
2. Collar
   
3. Containers
   
4. Mixing Tools & Tray
   
5. Hammer of 10 lb (4.5 kg) weight & having fall of 18 inches.
   
6. Sensitive weight balance.
   

THEORY

Compaction is the densification of unsaturated soil by the reduction in the volume of voids filled with air, while the volume of solids & water content remains the same. The major aims of compaction of soil are to increase shear strength, decrease compressibility, reduce permeability, & to control swelling & shrinkage of soil. The degree of compaction of soil is measured in terms of its dry density. The maximum dry density of soil occurs at optimum moisture content (OMC).The Modified Proctor Test is of great importance and is widely used in the construction of roads, highways, earth fill dams, earth filling, Airports, etc. In modified Proctor test, the soil is compacted in the given mold in Five (05) layers with a rammer of 10 lbs (4.5 kg) with a fall of 18 inches (45 cm).

PROCEDURE

1. Obtain soil sample from the field and break the soil lumps.
   
2. Sieve the soil on a #4 sieve. Collect all the minus 4 sieve materials in a large tray.
   
3. Add water to the sieved sample and mix thoroughly to bring the moisture content to about 3%.
   
4. Determine the weight of the Proctor Mold + Base Plate.
   
5. Attach the collar to the top of the mold.
   
6. Pour the moist soil in five equal layers. Compact each layer uniformly with the Standard Proctor rammer 25 times before each additional layer of loose soil is poured. At the end of the fifth layer of compaction, the soil should extend slightly above the top of the rim of the compaction mold.
   
7. Remove the collar carefully.
   
8. Trim excess soil with a straight edge.
   
9. Determine the weight of the Proctor Mold + Base Plate + Compacted Moist Soil.
   
10. Remove the base plate from the mold. Extrude the compacted moist soil cylinder using a jack.
    
11. Take a moisture can and determine its mass, W₁.
    
12. From the moist soil extruded in step 10, collect a moist sample in moisture can and determine the mass of moist soil + can, W₂.
    
13. Place the moisture can with soil in the oven to dry.
    
14. Break the rest of the soil cylinder by hand and mix with leftover moist soil. Add more water and mix to raise moisture content by 3% i.e. 6%.
    
15. Repeat steps 6-12. Continue the test until at least two successive decreased readings are obtained.
    
16. The next day, determine the mass of the moisture cans + soil samples, W₃.
    

OBSERVATION AND CALCULATIONS

Moisture content Determination (w)

Dry Density determination (ɣ_d)

The Result of Soil Compaction Test

The Maximum Dry Density of the Soil = _____________

The Optimum Moisture Content (OMC) = _____________(%)

Review Questions

1. What is the difference in the maximum dry density achieved in the standard & modified Procter tests?
   
2. Define compaction effort.
   
3. What is a line of optimums?