About

A structural foundation cushion serves to distribute loads evenly and break the capillary rise of ground moisture. However, ordering the exact geometric volume (L × W × H) results in a shortage on the job site due to compaction. Mechanical tamping reduces the void ratio of granular materials significantly. This tool calculates the "Loose Volume" required to achieve the desired "Compacted Volume" by applying specific material coefficients. Failure to account for this leads to work stoppages and additional delivery fees.

Formulas

The required order volume (V_loose) is calculated by determining the geometric volume of the trench and multiplying it by the material's Compaction Factor (k).

V_loose = (L × W × D) × k

Standard engineering estimates assume a k of 1.3 for sand, meaning 30% volume loss during tamping.

Reference Data

Material	Compaction Coeff	Density (kg/m³)	Uses
Fine Sand	1.30	1600	Pipe bedding, leveling
Coarse Sand	1.25	1700	Slab cushions
Crushed Stone	1.25	1500	Drainage layers
Gravel	1.20	1800	Sub-base
Clay Soil	1.35	1900	Backfill (non-structural)
Topsoil	1.40	1200	Landscaping
Mixed Aggregate	1.20	2100	Road base
Recycled Concrete	1.25	1750	Hardstand

Frequently Asked Questions

The Compaction Factor is a multiplier that represents the ratio of the material's volume in a loose state (in the truck) to its volume in a dense state (after mechanical tamping). A factor of 1.3 means you need 1.3 cubic yards to fill a 1 cubic yard hole.

This specific tool focuses on volume (cubic yards/meters) for ordering. Weight depends heavily on moisture content. Wet sand can weigh 20% more than dry sand for the same volume.

A uniform cushion thickness (usually 4-12 inches) ensures that the concrete slab settles evenly. Uneven thickness leads to differential settlement, causing cracks in the foundation.

It is industry standard to add an additional 5-10% "waste factor" on top of the compaction calculation to account for spillage, uneven subgrade, and corner losses.