Proctor Compaction Calculator

The Proctor test is a laboratory test that determines the maximum dry density (MDD) and optimum moisture content (OMC) of a soil. A soil sample is compacted at different moisture contents to find the density curve.

Standard Proctor uses a 2.5 kg hammer dropped 305 mm with 3 layers. Modified Proctor uses a 4.54 kg hammer dropped 457 mm with 5 layers, applying about 4.5× more energy.

Clay typically has a maximum dry density of 1,500–1,700 kg/m³ at an optimum moisture content of 18–25%. Sandy clay achieves higher densities (1,700–1,900 kg/m³) at lower OMC (12–16%).

Relative compaction is the ratio of field dry density to maximum dry density, expressed as a percentage. Specifications typically require 95–100% relative compaction for structural fills.

Below OMC, the soil is difficult to compact because particles cannot slide into position. The resulting density is lower and the soil structure may be unstable (honeycombed).

The zero air voids (ZAV) line represents the maximum theoretical density at a given moisture content assuming all air is expelled. No compaction test can exceed this line.

Field dry density is obtained via sand replacement test, nuclear density gauge, or rubber balloon method. The moisture content is determined from oven-dried samples.

Typical specifications: subgrade 95% MDD, sub-base 98% MDD, base course 100% MDD. These ensure adequate strength and minimize future settlement.