STandard Compaction Test

Title: The Standard Proctor/Compaction Test Objective: To measure the maximum dry density and optimum moisture content of a sample of soil.

Theory: A moisture-density relationship test or standard proctor test, measures the maximum dry density that a soil can reach under a specified compactive effort, and the optimum moisture content at which it can be compacted increases because of the lubricating effect of water. The air voids in the soil are reduced as the density increases, up to a point of maximum dry density and optimum moister content. At this point the air voids cannot be reduced further, and additional water results in lower density since the excess water must come between soil grains and a larger portion of the total volume is occupied by water which has a lower relative density than soil. A plot of dry density versus water content gives a moister density curve. The highest point on this curve is the maximum dry density for this soil at the specified compactive effort. The zero air voids curve gives maximum theoretical densities (no air voids) at indicated water contents. The standard compactive effort is 25 blows of a 2.5kg (5.5Ib) hammer falling 30 cm (12 in) on each of three layers of material in a mould 10cm (4in.) in diameter and 943.9 cm3 in volume.

Apparatus:      

Standard compaction mould Standard compaction hammer, with a 5lb mass falling a height of 12 inches with a sleeve Balance Oven Moisture cans Spatula

Procedure: 

A sample of dry soil of 15 kg weight was obtained for this experiment, and was break

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down to a size smaller than 4.75mm. A sum of ten moister cans were gathered, weighed and results were noted on a sheet of

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paper. A mass of the mould was taken without the collar and also noted. Three kilograms of soil from the sample that was obtained was distributed into five pans. The first three kilogram of soil was mixed thoroughly with 4 percent of water and then distributed into the mould with collar in three equal layers using a compacting hammer

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25 times for each layer. The collar was removed and a spatula used to trim excess compacted mixture of soil to

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the level of the mould. The mass of the compacted soil and the mould were taken and recorded. The soil was extracted and from the top of the mould and from the bottom of the mould

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and placed into two pre-weighted moister cans respectively and placed in the oven to dry. The procedure was repeated for the other 4 pans of 3 kg soil where the water content was increased for each by 2 percent until the combined mass of the mould and the soil decrease on at least two consecutive trials from the previous trial.

Observations:

In the Standard Compaction Test the following were observed.  The soil was collected and passed through a 4.5mm sieve.  The soil was collected and was not placed into the oven to bone dry, because it was a saturated surface dry sample.  For each batch of soil the calculated water content was added, however the beaker was not wiped out leaving behind water droplets which subtracted from the water content and add to the new calculated water content.  The triple beam balance was more accurate in measurement than the digital scale, because it had only two decimal places.  The diameter of the compacting hammer in comparison to that of the mould, prevented uniform compaction.

Discussion: The experiment was conducted to determine the maximum dry density and optimum moisture content of a specified soil. The results have shown that the soil’s maximum dry density is 15.078 kN/m3 and optimum moisture content is 8%. It can be discussed that the properties of the soil allowed it to absorb as much water before reaching a saturated state. The water helps to bond the molecules as well as reduce air voids to achieve maximum dry density or maximum bearing capacity after compaction. Conclusion: The objective of this test was to obtain maximum dry density and optimum water content for a soil, using the modified compactive method. As this is a way of improving soil strength for construction purposes. Therefore in concluding this report it can be said that maximum dry

density was obtained as well as optimum water content. The maximum dry density was found to be 15.078 kN/m3 and the optimum water content is 8%. Therefore it can be said that the Compaction Test was successful.