Swelling Pressure Test Clay minerals exhibit colloidal behaviour. That is, their surface forces have greater influence than the negligible gravitational forces.
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.
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.
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.
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
Factor contributing to swelling and swelling pressure Colloidal content – 1 mm and less Plasticity index (PI) Liquid Limit (LL) Shrinkage Limit (SL)
Experimental set up
Experimental Procedure Step 1: Place the perforated plate in the bottom.
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
Experimental Procedure Step 3: Fix the Proctor’s mould to the bottom of the frame
Experimental Procedure Step 4: Fix the cylinder to the Proctor’s mould
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
Experimental Procedure Step 6: Put the perforated plate on the top of the mould
Experimental Procedure Step 7: Place the plunger on the perforated plate and compact the soil sample
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.
Experimental Procedure Step 9: Put it the ball point on the perforated plate.
Experimental Procedure Step 10: Place the Proctor’s Mould in the water reservoir for the saturation.
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.
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.
Data Sheet
Data Sheet
Data Sheet
Data Sheet
Data Sheet
Data Sheet Swelling pressure
Data Sheet