1.1 ObjectiveTo obtain the moisture content-dry density relationship for a soil and hence to determineits maximum dry density (MDD) and optimum moisture content (OMC).1.2 IntroductionSoil compaction is an economical method of soil improvement, and it is often used tomake ground suitable for the foundations of roads and buildings. It is also used in theplacing of soil fills and in the construction of earth dams to ensure suitable soilproperties. The compaction is normally achieved through the input of energy into the soilby impact, kneading, vibration or static means.The extent of compaction depends on the moisture content of the soil and the compactiveeffort used. In a compaction test the object is to determine the optimum moisture contentand maximum dry density achievable with a given compactive effort. A plot of drydensity versus moisture content (Figure 1) indicates that compaction becomes moreefficient up to a certain moisture content, after which the efficiency decreases. Themaximum dry density is obtained at this optimum moisture content. If the compactionprocess were completely efficient, it would be possible to expel the air from the voids, inwhich case the dry density would correspond to a zero-air voids state (i.e. the samplewould be saturated with water). Since perfect compaction is not possible (except at highmoisture contents) the compaction curve will always fall below the ideal or zero-air voidscurve (Figure 1).