a) Removal of the electrostatic barrier that prevents aggregation of the particles by the addition of salt to a suspension or changing the pH of a suspension to effectively neutralize or "screen" the surface charge of the particles in suspension. This removes the repulsive forces that keep colloidal particles separate and allows for coagulation due to van der Waals forces.
b) Addition of a charged polymer flocculant. Polymer flocculants can bridge individual colloidal particles by attractive electrostatic interactions. For example, negatively-charged colloidal silica or clay particles can be flocculated by the addition of a positively-charged polymer.
c)Applying an electrical current, electrophoresis: The charged colloidal particles moves toward the electrode with the opposite charge. Particles will be neutralized and coagulate into larger particles and will settle out.
d) Physical deformation of the particle (e.g., stretching) may increase the van der Waals forces more than stabilization forces (such as electrostatic), resulting coagulation of colloids at certain orientations.
Swelling soils, also known as expansive soils, are ones that swell in volume when subjected to moisture.
These swelling soils typically contain clay minerals that attract and absorb water.
When water is introduced to expansive soils, the water molecules are pulled into gaps between the soil plates. As more water is absorbed, the plates are forced further apart, leading to an increase in soil pore pressure.(Handy, 1995).
Swelling soils contain a high percentage of certain kinds of clay particles that are capable of absorbing large quantities of water.
Soil volume may expand 10 percent or more as the clay becomes wet.
Exposure to natural or man-caused water sources during or after development results in swelling.
In many instances the soils do not regain their original dryness after construction, but remain somewhat moist and expanded due to the changed environment.
Table 1: Probable Expansion as Estimated from Classification Test Data (from Holtz and Kovacs, 1981) Degree of Expansion Probable Expansion (as a percent of the total volume change) 1 Colloidal Content (percent less than 1μm) Plasticity Index Shrinkage Limit Very High > 30 > 28 > 35 < 11 High 20 - 30 20 - 31 25 - 41 7 - 12 Medium 10 - 20 13 - 23 15 - 28 10 - 16 Low < 15 < 15 < 18 > 15