Compaction of soil :-
compaction of soil the process in which rapid reduction in volume takes place due to sudden application of loads caused by ramming, tamping, rolling and vibration.
Purposes of the compaction :-
(i) To increase the shear strength audits bearing capacity .
(ii) Stability of slopes.
(iii) To reduce compressibility and subsequent settlement under working loads.
(iv) To reduce soil permeability making it more difficult for water to flow through.
(v) Compaction can prevent liquefaction during earthquakes.
Compaction needed in the field :-
A fill is made by compacting successive horizontal layers. It is necessary to control the moisture content of the soil which is to be compacted. If the soil from the borrow pit is too dry, the deficiency of water in the soil may be made up by sprinkling water and mixing it thoroughly before compacting, whereas if the soil is too wet, it may be excavayed in advance and dried.
Difference between compaction and consolidation Compaction Consolidation :-
Compaction
1. It is almost a instantaneous .
2 . Soil is always unsaturated.
3. Densification is due to a reduction in the volume of air voids at a give water content.
4 Specified compaction techniques are used in this process.
Consolidation
1. It is time dependent phenomenon.
2. Soil is completely saturated .
3. Volume reduction is due to expulsion of pore water from voids .
4. It occurs on account of load placed
on the soil.
Standard Proctor Test
To study compaction characteristics in laboratory compaction tests are developed. The standard proctor test developed by R.R. Proctor (1933) is widely used. The equipments used in this test are (i) cylindrical metal mould with detachable base plate having an internal diameter of 4 inches (10.16 cm), internal height of 4.6 inches (11.68 cm) and internal volume of 1/30 cu. Ft. (945 cc) (ii) collar of 2 inches (5 cm) effective height (iii) rammer of mass 5.5 lb (2.5 Kg) with a height of fall in 1 foot (30.48cm).
The procedure consist of 
compacting the soil at different water contents are finding the corresponding dry densities. At each water content the mould with base plate is filled in 3 layers each layer being given 25 blows from the standard rammer. Dry density is plotted against water content to obtain the compaction curve. IS : 2720 (Part VII) 1965 recommends mould with a 100 mm internal diameter and 127.5 mm effective height whose internal volume is 1000 ml. The rammer has mass of 2.6 Kg and free fall of 310 mm.
compacting the soil at different water contents are finding the corresponding dry densities. At each water content the mould with base plate is filled in 3 layers each layer being given 25 blows from the standard rammer. Dry density is plotted against water content to obtain the compaction curve. IS : 2720 (Part VII) 1965 recommends mould with a 100 mm internal diameter and 127.5 mm effective height whose internal volume is 1000 ml. The rammer has mass of 2.6 Kg and free fall of 310 mm.
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