Compaction The process of vibrating or tamping down loose soil, gravel, or wet concrete to eliminate air voids and increase its density and load capacity.
Proper compaction of both the dirt subgrade and the gravel base is what prevents a sidewalk from settling and cracking down the road. If a contractor pours concrete over uncompacted soil, the heavy weight of the concrete and pedestrians will cause the ground to sink, leading to trip hazards. NYC DOT standards require mechanical plate compactors on all sidewalk subbases.
Frequently Asked Questions About Compaction
What is compaction in sidewalk construction?
Mechanically tamping or vibrating soil and gravel to remove air voids and increase density before concrete is placed.
Why is compaction the most important hidden step?
Concrete poured over loose soil settles under load, producing the cracking, sunken flags and rocking slabs that generate violations.
How is it done?
With mechanical plate compactors, working the subgrade and then the base material in layers rather than all at once.
Can you tell if compaction was skipped?
Not by looking at the finished surface, which is why it is a common corner to cut. The failure shows up as settlement in the following years.