Standard Proctor Test – its 5 [Procedure Steps, Purposes & Tips]

The standard proctor test is a test that is used to determine the compaction of different types of soil and properties of soil with a chance in moisture content and the standard proctor test is a laboratory geotechnical testing method.

This test is used to determine the maximum dry density for any soil and to determine how much soil must be compacted to ensure the stability of a structure and prevent damage from settling. The standard proctor test is generally performed in the labs.

The standard proctor test is a soil compaction test which ensures that how its density changes with moisture content and it also reveals the maximum density achievable for that particular soil.

This test is essential because of how much soil types vary by region and site and soil’s initial moisture content can change from one location to another location, these are the reasons for the standard proctor test.

Fundamental of Compaction:

According to standard proctor test, the compaction of soil depends upon the following factors;

1. Soil Type
2. Moisture Content
3. Compaction Effort
4. Dry Density of Soil

Soil Type & Moisture Content:

The dry density of soil mass varies with moisture content for a given type of soil and Compactive effort.

The internal friction and adhesion between the particles contribute to the resistance to compaction, at low moisture content. If the moisture content increases the particles develop moisture films around them which help in lubricating the particles.

The moisture content increase beyond a certain particular value of the moisture content it does not increase further and the water at this stage starts replacing the soil particles.

Compaction Effort:

To a greater extent the compacting of soil, both the magnitude of compacting energy and the type of compaction effort influence.

By vibration, in the field hand-operated vibrating plates cohesionless soils are efficiently compacted and for compaction of sand, gravel, etc motorized vibratory rollers of various sizes are used.

In the laboratory, fine-grained soils may be compacted by falling weights and hammers by special kneading compactors and even under static pressure.

Dry Density of Soil:

As we know that normal soil consists of solids, moisture content, and air and by finding out the weight of soil per unit volume usually the bulk density of soil is calculated.

For root growth, a bulk density of over 1.6 gm/cm3 is not helpful.

Apparatus for the Standard Proctor Test:

There are following material used in the standard proctor test as given below;

1. A cylindrical metal mold having the internal effective height of 4.6” and an internal diameter of 4” and mold should have a base plate and collar of 2 inches.
2. Rammer having a fall of 12 inches of 2.5 kg weight with a 2 inches diameter of the flat circular face.
3. Sensitive balance, 0.1 gram to 1 gram sensitivity.
4. Thermostatically controlled oven
5. Steel straight edge
6. Moisture containers
7. Sieve
8. Scoop and tray
9. Graduated cylinder
10. Mixing tools like a trowel, spoon, etc.

The Procedure of Standard proctor Test:

There are following steps in the procedure of standard proctor test as given below;

Step 1:

Take a sufficient quantity of soil, air dry and with a rubber mallet pulverize it and through a sieve, sieve the soil and reject the coarser material.

Take about 3 kg of soil and to bring its water content to about 5% below the estimated moisture content, add water, and mix it thoroughly.

Step 2:

Clean the mold and without collar measure its diameter, height, and weight.

To each layer fit the collar and compact the moist soil in three equal layers by the rammer with evenly distributed blows.

To the total height of the mold with collar use 25 blows for 4 inches diameter and for 6 inches diameter using 56 blows.

Step 3:

With straight steel, edges remove the collar and trim the compacted soil and clean outside of the mold and base plate and weigh it.

From the mold remove the soil and for water content determination split it and take about 100 grams sample.

Step 4:

Now, break the soil lamps and with remaining soil in tray mix it and to increase the water content by 2% to 3% add more water, and until the mass of the compacted soil decreases repeats the compaction procedure for each increment of water.

For each trail and corresponding dry density calculate water content.

Step 5:

Between water content and dry density plot the compaction curve and as optimum moisture content and the corresponding dry density as maximum dry density, note the water content against the peak of the curve.

Purposes of the Standard Proctor Test:

There are following purposes for which the standard proctor test is taken such as;

1. Between moisture content and dry density it determines the relationship graph.
2. For the maximum dry density of soil that must be achieved in the field, this test determines the maximum dry density.
3. To determine the optimum moisture content of the soil this test is used.
4. For achieving the desired density it establishes a moisture range that can ensure minimum compaction effort.

Observations and Calculations:

Tips for Easier standard Proctor Test:

There are following tips for an easier, more effective soil compaction test as given below;

Easy Reference for Optimum Moisture Content:

For estimating optimum moisture content in the soil there is a simple trick and the optimum moisture level should be roughly equivalent to the moisture level in a soil sample that stays put when manually lump it together but if you try to bend the top it breaks apart cleanly.

Expedite Initial Air-Drying:

If you break down large clumps in the soil, the initial air-drying process can be expedited if a cohesive soil sample is used and be sure not to crush the individual particles.

Use a Soil Ejector:

To get specimen out of soil compaction mold more easily and completely, a soil ejector can be used and this process ensures to get the most accurate dry weight.