Definition
Backfill is the process of refilling an excavated area with material, typically soil, gravel, or sand, after construction work such as foundation pouring or utility installation. Proper backfill provides structural support, drainage, and protection for foundations. The material is typically placed in layers (lifts) and compacted to prevent future settling.
Formula
Account for 15-25% compaction when ordering backfill material. If excavating 100 cubic feet and the foundation occupies 30 cubic feet, you need 70 cubic feet of backfill, but order about 82 cubic feet to account for compaction.
Example
Foundation Backfill Example
After pouring a foundation that is 40 feet long, 2 feet wide, and 8 feet deep (640 cubic feet), the excavation was 10 feet wide. The backfill volume is approximately (10-2) x 40 x 8 = 2,560 cubic feet. With 20% compaction, order about 3,072 cubic feet or 114 cubic yards of backfill material.