Field Dry Density (FDD) Test on Soil

The Field Dry Density (FDD) Test is performed to determine the compaction quality of soil at site and to verify whether the required compaction has been achieved.

Purpose of FDD Test

· Determine in-situ dry density of soil

· Check degree of compaction

· Ensure proper soil compaction

· Quality control of earthwork

Methods of FDD Test

· Sand Replacement Method

· Core Cutter Method

· Nuclear Density Method

Sand Replacement Method Procedure

1. Prepare and level the test surface

2. Place tray with central hole

3. Dig soil carefully

4. Collect and weigh excavated soil

5. Fill hole with calibrated sand

6. Measure weight of sand filling hole

7. Calculate volume of hole

8. Determine bulk and dry density

Formula

Bulk Density (γ) = W / V

Dry Density (γd) = γ / (1 + w)

Example Calculation

Weight of excavated wet soil = 3200 g

Water content = 12%

Weight of sand filling hole = 1800 g

Density of calibration sand = 1.50 g/cc

Step 1: Volume of Hole

V = 1800 / 1.50

V = 1200 cc

Step 2: Bulk Density

γ = 3200 / 1200

γ = 2.67 g/cc

Step 3: Dry Density

γd = 2.67 / (1 + 0.12)

γd = 2.38 g/cc

Degree of Compaction

% Compaction = (Field Dry Density / Maximum Dry Density) × 100

If MDD = 2.50 g/cc

% Compaction = (2.38 / 2.50) × 100

% Compaction = 95.2%

Standard Codes

IS 2720 Part 28

ASTM D1556

Applications

· Road construction

· Building foundations

· Railway projects

· Backfilling works

· Embankment construction