Field Density Test

The field density test (FDT) measures the in-situ dry density of a compacted earthwork layer to verify the achieved degree of compaction against the laboratory MDD. The two common Indian methods are the sand-replacement method (IS 2720 Part 28 — a calibrated sand fills the excavated hole to give its volume) used for most soils including gravelly, and the core-cutter method (IS 2720 Part 29) used for soft, fine, cohesive soils free of stones.

The field dry density is computed from the wet weight, hole volume and field moisture, then expressed as a percentage of MDD. Each compacted lift is tested at a specified frequency (e.g. one test per 500-1000 m² or per 250 m³ per MORTH) before the next lift is allowed — a classic ITP hold-point. Failing tests require re-rolling, moisture correction or removal of the lift.