1. Swelling Pressure Test
Clay minerals exhibit colloidal behaviour. That is, their surface forces have greater influence than the negligible gravitational forces.

2. Expansive clays are a source of concern because they shrink and swell according to their moisture content.
If this uneven shrink and swell is not considered during construction, structures such as houses can literally break apart.
Highways are also susceptible to damage from expansive clays resulting in higher maintenance costs.
Many expansive soil problems can be accommodated through engineering techniques employed prior to construction.
Bentonite clay is highly expansive.

3. Theory
Irrespective of high swelling potential, if the moisture content of the clay remains unchanged, there will be no volume change and structures founded on clays will not be subjected to movement caused by heaving.
When moisture content of the clay is changed, volume expansion both in horizontal and vertical direction may take place.
Complete saturation is not necessary to accomplish swelling.
Slight change of moisture content, at the order of 1.0 to 2.0% magnitude is sufficient to cause detrimental swelling.

4. Definition of swelling pressure
The magnitude of external pressure or stress required to maintain the content volume of the soil during its saturation
Methods to obtain swelling pressure
Allow the soil to swell completely and then recompress it back to its original volume.
At each stage during swelling, compress it back to it s original volume.
Consolidometer method in which swell of several identical samples is obtained under different external pressures and from the plot of swell/compression versus external pressure at constant volume is determined.

5. Factor affecting swelling pressure
Initial water content
Initial compaction density
Method of compaction
Final degree of saturation
Note:
If the skin friction is eliminated, the swelling pressure is found to be independent of size of the test specimen

6. Factor contributing to swelling and swelling pressure
Colloidal content – 1 mm and less
Plasticity index (PI)
Liquid Limit (LL)
Shrinkage Limit (SL)

7. Experimental set up

8. Experimental Procedure
Step 1: Place the perforated plate in the bottom.

9. Experimental Procedure
Step 2: Place the filter paper on the perforated place, so that soil particles should not escape from the mould along with the water

10. Experimental Procedure
Step 3: Fix the Proctor’s mould to the bottom of the frame

11. Experimental Procedure
Step 4: Fix the cylinder to the Proctor’s mould

12. Experimental Procedure
Step 5: Measure the internal and external diameter of the mould. Measure the height of the mould Calculate the volume of the cylinder

13. Experimental Procedure
Step 6: Put the perforated plate on the top of the mould

14. Experimental Procedure
Step 7: Place the plunger on the perforated plate and compact the soil sample

15. Experimental Procedure
Step 8: Remove the plunger and cylinder. Now calculate the volume the perforated plate occupied the mould. Find out the Net Volume of the compacted soil sample.

16. Experimental Procedure
Step 9: Put it the ball point on the perforated plate.

17. Experimental Procedure
Step 10: Place the Proctor’s Mould in the water reservoir for the saturation.

18. Experimental Procedure
Step 11: Put the Proctor’s Mould in the water reservoir for the saturation. Attach the complete set up to dial guage. Allow the soil sample to swell for 28 days.

19. Precautions
Soil sample should be kept always submerged in water reservoir, so that clay sample may be saturated through both ways. Mould walls should be as smooth as possible to avoid wall friction between soil and mould. Therefore silicon grease should be used. The application of pressure to bring the soil sample to its initial volume should be continuous, because intermittent pressure may cause elastic rebound, consequently affects the results. Perforated plunger plate should be partly out of the mould, so that it may removed easily without any difficulty.

20. Data Sheet

21. Data Sheet

22. Data Sheet

23. Data Sheet

24. Data Sheet

25. Data Sheet
Swelling pressure

26. Data Sheet