It's not hard to spot some of the results of poor soil compaction around a house. Cracked foundations. Concrete steps that lean away from the house. A cracked and settled garage slab with one part higher than the other. Rain water running toward the foundation instead of away from it. All these flaws mar appearance and reduce resale value for the property but could have been easily avoided without spending a lot of money. Compacting the soil during construction costs much less than correcting settlement problems after they occur.
WHERE IS COMPACTION NEEDED?
Use compaction whenever the soil is disturbed during construction or when it's used for fill. Compact disturbed soil beneath footings, slabs, basement floors, patios, garage floors, driveways, concrete steps and sidewalks. If a sand, gravel, or crushed stone base is used beneath a slab, compact it too. Always compact fill soils before placing footings or slabs on them. Also compact backfill next to footings and foundation walls.
EFFECT OF SOIL TYPE AND MOISTURE CONTENT
For compaction purposes, soils are considered to be either granular or cohesive. Granular soils contain primarily gravels, sands, and silts and feel gritty when rubbed between the fingers. They have little or no plasticity when wet and no cohesive strength when dry. Cohesive soils contain clay and feel smooth and greasy when rubbed between the fingers. Cohesive soils are plastic and sticky when moist and have a high dried strength.
CHOOSING AND USING THE RIGHT COMPACTION EQUIPMENT
For large fill areas, rolling is the fastest, most efficient compaction method. Hand-held compactors can be used in smaller areas and for places that larger mobile equipment can't reach. For granular soils, vibrating plate compactors work best. Rammers or impact type machines are used for cohesive soils.