Engineering Report

Standard Proctor Compaction Test and Modified Proctor Compaction Test

Objective of this experiment is to determine optimum moisture content and maximum dry unit weight of compaction for soils that is utilized for specification of field compaction.

Description of Soil Samples:

The soil use in the lab experiment was Limerock soil.
Description of Test Methodology:
At first about 10 lb. (44.48 N) of air-dry soil on which the compaction test conducted was collected and all the soil lumps were broken. The soil was sieved on a No.4 sieve and all of the minus-4 material were collected in a large pan. Then enough water was added to the minus-4material and mixed it in thoroughly to bring the moisture content up to about 5%.The weight of the Proctor mold + base plate ('W1') was determined. Then the extension was attached to the top of the mold. The moist soil was poured into the mold in three equal layers and each layer should be compacted uniformly by the Standard Proctor hammer 25 times before the next layer of loose soil was poured into the mold. After this, the top attachment was removed from the mo1d. Using a straight edge, the excess soil was trimmed above the mold. In the next step, the weight of the mold + base plate + compacted moist soil in the mold (W2, in lb.) was determined. Then the base plate was removed from the mold. After this, the compacted soil cylinder was extruded from the mold by using a jack and a moisture sample was collected in a moisture can and put it into the oven to dry to a constant weight. Then the rest of the compacted soil (to No. 4 size) was broken by hand, and it was mixed with the leftover moist soil in the pan. In the next step, more water was added and mixed to raise the moisture content by about 2%. Above process was repeated and final dry weight of soils in the moisture cans were determined.

Test Results:

Graph of Dry Unit Weight vs. Moisture Content
Discussion:
But it has been found out that one value of moisture content was negative in Standard Proctor Test and this has happened due to error. This error may be caused by wrong measurement or mistake occurred during entering data.
The difference between the Modified Proctor Test and Standard Proctor Test lies in the compaction energy. At first Standard Proctor Test was widely used but now Modified Proctor Test is widely used, as greater and more relevant compaction is used in later case. Knowledge of optimum moisture content is important to reduce air content, increase strength of soil.

Conclusion:

The experiment was carried out safely and successfully. However, one data of moisture content was found out negative which is absurd. It has been found that the maximum dry unit weight of compaction increases with the increase of the compacting energy as well as the optimum moisture content decreases with the increase of the energy of compaction.