Compaction Test

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Compaction Test
Introduction
“Compaction is the process of increasing the density of a soil by packing the particles closer together with a reduction in the volume of air.” (Craig, 2004)
Compaction tests are important in earthworks construction as

The aim of this test was to find the relationship between moisture content and dry density of an engineering soil. This information could be used to find the optimum moisture content and the maximum dry density. At this value of maximum dry density the void ratio, porosity, degree of saturation and air content could also be calculated.

Apparatus
• Metal mixing bowl
• Palette knife
• Measuring cylinder
• Steel Mould of capacity 1L with base plate and collar
• 2.5kg Compaction rammer
• Electronic scales
• Additional apparatus for determination of moisture content as described in BS 1337-2: 1990 o Metal tins for small samples o Oven to dry samples in tins

Method
The method used was a standard method for compaction test using a 2.5kg rammer outlined in BS 1377-4: 1990.
• Measure 5kg of soil on the electronic scales and add to the mixing bowl.
• Add 250ml of water to the sample to set the moisture content at 5% then mix the sample.
• Record the mass of the mould with the base plate attached.
• Attach the top collar to the mould.
• Add enough soil to reach about a third the total height of the mould.
• Compact the soil by applying 27 blows with the 2.5kg rammer spread evenly across the surface of the soil.
• Add another two layers of soil, compacting in the same way, allowing the final level of soil surface to reach approximately 10mm above the top of the mould.
• Detach the top collar and remove the excess soil so that the surface is level with the top of the mould.
• Re...

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...ecomes;
Sr = ((w/100) x 2.12 x 1000) / Vv
Sr = ((8/100) x 2.12 x 1000) / 208.955
Sr = 0.812 = 81.2%
• Air content
Air Content = Volume of Air / Total Volume
A = VA / V

The volume of air can be calculated using the equation Vv = VA +Vw. The volume of water can be calculated due to the knowledge that Vw = Mw, Mw = w/100 x Ms and Ms = ρdV.
So Vw = 169.6
VA = 208.955 – 169.6
VA =39.355
A = VA / V
A = 39.355/1000
A = 0.0394 = 3.94%

Analysis

The results show that the compaction test was successful as a correct relationship between dry density and moisture content has been established. The deduced values for maximum dry density and optimum moisture content lie within an acceptable range and the calculated air content is in agreement with the air content lines plotted on the graph which show the value of air content at the maximum dry density to be between 0% and 5%.

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