But, it is essential to add certain amount of water to achieve maximum density of soil.
This concept was first introduced by R. R. Proctor in 1933. He showed that, for a given compaction effort, dry density of a soil depends on the water amount of that particular soil. That means, to obtain maximum dry density of a soil, a certain amount of water must be present on that soil.
To determine the required quantity of water to obtain the maximum dry density for a particular soil a test is done in laboratory, that is the standard proctor test.
In this test, a selected soil sample is collected from field and compact into a cylindrical mould at various water contents in laboratory.
The volume of cylindrical mould is 1000 cubic-centimeter. This mould is filled by three layer step by step with the given soil sample. Each layer is compacted by a rammer. This rammer is dropped from a determined height for equal compaction effort.
This procedure is done several times with the soil of different water content. And results are taken for these tests.
All the results are then showed in a graph. In that graph, X-axis shows the water content and Y-axis shows dry density of the sample soil. In between, a curved line is drawn with all of the results of same compaction effort. From that curved line we can determine the required water quantity for obtaining maximum dry density of selected soil with a given compaction effort. See the picture above.
Based on this result, contractors can choose the type and amount of compaction.
But, the problem is that, this Standard Proctor Test doesn’t reproduce same result in the field. That’s why the Modified Proctor Test is developed for reproducing more accurate result in field. Yet, the Standard proctor test is used in many countries for soil compaction.
Which test method is used in your region? Please share in comments…