Compaction test
Testing Objectives
Determination of maximum dry unit weight which can be used for specification of field compaction
Relationship between the moisture content and density of soils.
Need and Scope
The knowledge of maximum dry density enables to improve the in situ ground conditions which otherwise may be unsuitable for construction. This value ensures maximum density (number of soil particles) accommodated at the most optimum moisture level to ensure enhanced strength.
Apparatus Required
Proctor mould with a detachable collar assembly and base plate.
Rammer weighing of 2.5 kg and equipped to provide a height of drop to a free fall of 30 cm.
Sample extruder.
A sensitive balance.
Straight edge.
Squeeze bottle
Mixing tools such as mixing pan, spoon, towel, spatula etc.
Moisture tins.
Drying Oven
Test Procedure
1. Obtain approximately 10 lb (4.5 kg) of soil breaking all the lumps and passing US No. 4 sieve.
2. Add approximate amount of water to increase the moisture content by about 5%.
3. Determine the weight of empty proctor mould without the base plate and collar. W1, (lb).
4. Fix the collar and base plate. Distribute the soil into three equal parts.
5. Place the first part in the Proctor mould and compact the layer giving 25 blows.
6. Scratch the layer with a spatula forming a grid to ensure uniformity in distribution of compaction energy to the subsequent layer. Place the parts 2 & 3 repeating the above two steps.
7. The final layer should ensure that the compacted soil is just above the rim of the compaction mould when the collar is still attached.
8. Detach the collar carefully without disturbing the compacted soil inside the mould and using a straight edge trim the excess soil leveling to the mould.
9. Determine the weight of the mould with the moist soil W2, (lb). Extrude the sample and break it to collect the sample for water content determination preferably from
the middle of the specimen.
10. Weigh an empty moisture can, W3, (g) and weigh again with the moist soil obtained from the extruded sample in step9, W4, (g). Keep this can in the oven for water
content determination.
11. Break the rest of the compacted soil with hand (visually ensure that it passes US Sieve No.4). Add more water to increase the moisture content by 2%.
12. Repeat steps 4 to 11. During this process the weight W2 increases for some time with the increase in moisture and drops suddenly. Take two moisture increments
after the weights starts reducing. Obtain at least six points to plot the dry unit wt, moisture content variation.
13. After 24 hrs recover the sample in the oven and determine the weight W5, (g).
The Modified compaction procedure is similar to the above with a change in the compactive effort. The rammer used in the modified compaction is a 10 lb with a
height of drop of 18".
Reporting the results
The results shall be the maximum dry unit eight and the optimum moisture content at which this value is obtained
Calculations
| Test | 1 | 2 | 3 | 4 | 5 | 6 |
| 1. Weight of the mold, W1, (lb) | | | | | | |
| 2. Weight if the mold + moist soil, W2 (lb) | | | | | | |
| 3.Weight of the moist soil, W2-W1, (lb) | | | | | | |
| 4. Moist unit weight, γb = [(W2-W1)/(1/30)], (lb/ft3) | | | | | | |
| 5. Moisture can number | | | | | | |
| 6. Weight of moisture can, W3, (g) | | | | | | |
| 7. Mass of can + moist soil, W4, (g) | | | | | | |
| 8. Mass of can + dry soil, W5, (g) | | | | | | |
| 9. Moisture content, w(%)= [(W4-W5)/(W5-W3)] x 100 | | | | | | |
| 10. Dry unit weight of compaction γd (lb/ft3) = γb/[1+(w/100)] | | | | | | |
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