Standard Proctor Soil Testing

The Standard Proctor Test is a laboratory test used to determine the optimum water for a given compaction energy for a given soil. This test is especially useful when determining the relationship between water content and the dry unit weight of soils to establish the maximum density of a soil needed for a fill area.

The laboratory test serves a two-fold purpose by first determining the maximum density achievable for the materials in the field, as a reference. Secondly, it measures the effect moisture has on soil density. These values are often determined before earthwork begins to provide reference values for field testing.

In the early 1930s, University of California, Berkeley student Ralph R. Proctor developed a method for determining the maximum density of soils. He established a laboratory procedure to define the moisture-density relationship of compacted, cohesive soils. Values from the Standard Proctor Test could be compared to unit weights and moisture of the same soils compacted in the field as structural earth fills to determine their degree of density and predict future performance. In 1958, the Modified Proctor Test was developed as an ASTM standard and it’s still used today concurrently with the standard test.

Equipment for Proctor Soil Test

• Soil Molds with either 4in or 6in diameters to hold compacted samples
• Manual Soil Compactors enables compaction of an individual 4in Marshall asphalt sample into a stationary mold using a manually operated drop hammer.
• Mechanical Soil Compactors automatically count the number of hammer blows and shut off when a preset number is reached for improved accuracy, operation and reliability
• Balance compliant with D4753 and 1-g readability to weigh the dry unit sample after compaction.
• Drying Oven that maintains uniformity to 230 ± 9°F (110 ± 5°C), to dry sample prior to testing
• Straightedge to level and trim specimens held in the molds
• E11 Sieves for particle size determinations
• Pans for air drying, processing and mixing

Proctor Soil Test Procedure

1. Apply 25 blows from the rammer dropped from a height of 300mm above the soil.
2. Distribute the blows uniformly over the surface and ensure that the rammer always falls freely and is not obstructed.
3. Place a second quantity of moist soil in the mould such that when compacted it occupies a little over two-thirds of the height of the mould body.
4. Repeat procedure once more so that the amount of soil used is sufficient to fill the mould body, with the surface not more than 6mm proud of the upper edge of the mould body.

Modified Proctor Soil Test

1. As for 2.5kg rammer method, but the rammer has a weight of 4.5kg and dropped from a height of 450mm.
2. In this compaction test the mould and the amount of dry soil used is the same as for the 2.5kg rammer method but
   the heavier compactive effort is applied to the test sample.
3. The rammer has a mass of 4.5kg with a free fall of 450mm above the surface of the soil.
4. The number of blow per layer remains the same, 25, but the number of layers compacted is increased to five.
5. This is similar to the Proctor Test except a hammer is used to compact material for greater impact. The test is normally preferred in testing materials for higher shearing strength.

The compaction energy is:

E = No. of blows per layer x No. of layers x Weight of hammer x Height of drop of hammer / Volume of mould