Compaction tests

soil compaction

1. Compaction tests AMI D. JASANI 136120306020 GUIDED BY: V.K.ZAA

2. Definition of compaction Compaction is the process by which soil particles are packed more closely together by dynamic loading such as rolling, tamping or vibration it is achieved through the reduction of air voids with little or no change in water content of soil.

3. Objectives for Compaction Compaction improves the engineering properties like shear strength, density, permeability etc. of the f Increasing the bearing capacity of foundations; Decreasing the undesirable settlement of structures; Control undesirable volume changes; Reduces the chances of slope stability problems like landslides. Reduces the amount of water that can be held in the soil by decreasing the void ratio and thus helps in maintaining the required strength.

4. Purpose of compaction test: The purpose of a laboratory compaction test is to establish a relationship between dry density and moisture content for a soil under controlled conditions. R.R. Proctor (1933) was the first to develop a method of assessing compacted fill that has since become a universal standard and the test is known as standard proctor test. proctor test is also known as light compaction test as per BIS. AASHO developed a modified test to give a higher standard of compaction and is known as modified proctor test. The same is also known as heavy compaction test as per BIS.

5. Laboratory compaction test Standard proctor test Modified proctor test As per BIS( buero of Indian standards) Light compaction test Heavy compaction test Details of the apparatus Cylindrical model Internal diameter 100 mm 100 mm Height 127.3 mm 127.3 mm Volume 1000 cc 1000 cc Rammer Mass 2.6 kg 4.89 kg Drop 310 450 Force diameter 50 mm 50 mm Comp-active effort 592 kJ/m3 2700 kJ/m3 No . of layers compacted 3 5 No. of blows 25 25 Height of free fall 31 cm 45 cm

6. Light Compaction Test Apparatus: - cylindrical metal mould - rammer - The mould is fitted with detachable base plate and collar.

7. Procedure :- The empty mould is attached to the base plate and weighed. The collar is then attached to the mould at the top. The wet and matured soil is placed in the mould and compacted by giving 25 blows of rammer uniformly distributed over the surface. The soil is compacted in three layers.

8. The volume of soil taken in each layer is such that its compacted height is about one third of the total height of the mould. Before placing the second layer, the top of the first compacted layer is scratched for proper bonding of both the layers. The second and third layers are also compacted by giving 25 blows of rammer. The collar is then removed and excess soil is trimmed to level with the top of the mould.

9. The mould along with the compacted soil is then weighed to get the mass of the compacted soil. A representative sample is taken from the centre of compacted soil for moisture content test. The soil is then removed from the mould and is mixed with the original sample. About 2% more water is added in the sample and the test is repeated. The procedure is continued until the mass of compacted soil begins to decrease.

10. The bulk density and dry density for the test is calculated from the known values of mass of soil, volume of soil equal to volume of mould and the moisture content of each test Bulk density g= Mass of soil / Volume of Soil = M/1000 gm/c.c. Dry density of soil, Y d= g /1+m gm/c.c. where M = Mass of soil in gm m = water content or moisture content Volume of soil = Volume of mould = 1000 c.c.

11. A graph is plotted between % water content and dry density the curve obtained is called compaction curve as shown in figure. It is clear from the graph that dry density of soil goes on increasing as the water content is increased, till maximum density is reached. The water content corresponding to the maximum dry density is called optimum moisture content (OMC).

12. Heavy Compaction Test Also known as modified compaction test. The modified proctor test was developed and standardized by AASHO to represent heavier compaction required for heavier transports. The calculation of dry density and maximum dry density is similar to that of standard proctor test. Figure shows modified proctor test curve.

13. In this test, the water content dry density curve lies above the standard proctor test dry density curve lies above the standard proctor test curve and has its peak relatively placed towards the left. Thus for a same soil, the effect of heavier compaction is to increase the maximum dry density and to decrease the optimum water content. The comp-active transmitted by the modified. AASHO test hammer is about 4.5 times the energy transmitted by Proctor’s hammer.

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