Field methods for in-situ density

The in-situ density is found by taking out a known volume of soil from the ground and weighing it; the water content gives the dry density, $\gamma_d = \gamma/(1+w)$. The method depends on the soil type.

1. Core cutter method (IS 2720 Part 29)

Used for soft to medium cohesive soils that stand without crumbling. A steel cylinder (usually 100 mm dia, 130 mm high) is driven into the ground with a dolly and rammer, dug out with the soil inside, trimmed and weighed. Volume = volume of the cutter, so $\gamma = W/V$.

2. Sand replacement method (IS 2720 Part 28)

Used for gravelly and sandy soils, hard clay, or where the core cutter cannot be used. A hole is dug, the soil is weighed, and the hole volume is found by filling it with calibrated dry sand (Ottawa/ standard sand) from a pouring cylinder.

$$V = \frac{W_{sand\ in\ hole}}{\gamma_{sand}}$$

3. Water displacement method

Used for soils with irregular holes. The hole is lined with a thin rubber balloon or plastic sheet and filled with a measured volume of water to find the volume.

4. Rubber balloon method

A balloon density apparatus measures the volume of the hole directly from the water pressed into the balloon.

5. Nuclear density gauge

Gives density and water content quickly by gamma-ray backscatter; used for rapid quality control of compaction.

6. Wax-coated lump (paraffin) method

For cohesive, hard lumps of irregular shape; the lump is coated with wax and its volume found by water displacement.

Selection: core cutter for soft fine-grained soil, sand replacement for coarse soils, and nuclear gauge for large-scale quick control.