Sand Replacement Field Density Test (BS 1377-9 / ASTM D1556): Method & Apparatus

The sand replacement test measures the in-situ dry density of compacted soil — the standard field check that earthworks have achieved the density specified from the laboratory Proctor test.

What the Test Measures

A hole is excavated in the compacted layer, the soil is weighed and its moisture measured, and the hole volume is determined from the mass of calibrated uniform sand needed to fill it. Dry density then follows directly, and is compared with the Proctor maximum as the degree of compaction.

Apparatus Required

• Sand pouring cylinder (small 115 mm for fine soils, large 215 mm for coarse) with tray and cone
• Calibrated uniform test sand (typically 600 µm–300 µm, free-flowing, oven dry)
• Metal tray with central hole, digging tools, airtight containers
• Balance (1 g), moisture tins and oven or field moisture kit

Test Procedure

1. Calibrate: determine the sand’s bulk density and the mass of sand filling the cone.
2. Level the surface, seat the tray, and excavate a neat cylindrical hole (approx. 150 mm deep for a 215 mm cylinder), saving all soil.
3. Weigh the excavated soil; take a representative moisture sample.
4. Fill the hole from the pouring cylinder; from the mass of sand used minus the cone allowance, compute hole volume.

Calculation & Reporting

Bulk density ρ = mass of excavated soil / hole volume; dry density ρ_d = ρ / (1 + w). Degree of compaction = ρ_d / ρ_{d,max(Proctor)} × 100%. Report layer, location, moisture content and the Proctor reference used.

Acceptance Criteria

Typical specification: 90–95% of modified Proctor maximum for general fill, 95–98% for sub-base/subgrade layers under pavements. Moisture at test should normally sit within ±2% of optimum unless the spec states otherwise.

Frequently Asked Questions

When is sand replacement preferred over a nuclear density gauge?

Sand replacement is the referee method: no licensing, no calibration drift, valid in all materials including coarse fills where gauges struggle. Gauges win on speed for high-frequency QC, but disputed results fall back to sand replacement.

Why must the test sand be re-calibrated regularly?

Bulk density changes with humidity, grading wear and handling. Re-calibrate whenever a new batch is used, after rain exposure, and at the frequency in your quality plan (commonly weekly on active sites).

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