- Increase load-bearing capacity
- Prevent sail settlement
- Make the foundation more stable
- Reduce water seepage, swelling and contraction
This is officially categorized into 15 groups by the AASHTO (American Association of State Highway and Transportation Officials). But for practical purposes, there are three basic soil groups: Cohesive, Granular, Organic (this soil is not suitable for compaction). Every soil type behaves differently, so each type has its own requirements for compaction methods. A soil’s makeup determines the best compaction method to use. And anyone can determine what type of soil it is by picking it up and trying to roll it into a ball. If its sticks together, it’s cohesive – if it doesn’t, it’s granular.
Clay is cohesive and its particles stick together, so a machine with a high impact force is required to ram the soil and force air out to make sure there are no air voids. A rammer is the best choice, or a pad-foot vibratory roller if higher production is needed.
Since granular soils are not cohesive, and the particles require a shaking or vibratory action to move them, vibratory plates are the best choice.
While it is not a soil, it still needs to be compacted. Asphalt is considered granular due to its base of mixed aggregate sizes (crushed stone, gravel, sand and fines) mixed with asphalt. As a result, asphalt must be compacted with pressure and vibration.