Theory of compactionResults of the tests show that the compaction dry density increases when soil compaction with increasing moisture content under any compaction effortTo that of the sample humidity maximum dry density and then decreases after the increase in humidity at the maximum ....There are many theories to explain this, including :That if the moisture in the soil is low , the particle Tnglv with a thin layer of water and air that separates these granules acquires an air pressure where the air is initially connected to the atmosphere .If Dmokt grained with some connection to refrain air voids in the atmosphere , the pressure of air trapped in the blanks than by air pressure depends on the degree of convergence of some of the granules and the volume of air trapped in the pockets of the convergence of the resulting granules .And whenever a large volume of trapped air whenever the pressure was small and vice versa .The case of the maximum moisture content resulting in a decrease in the proportion of trapped air the remaining portion of the compaction effort until it fails to overcome the frictional resistance between the small particles , resulting in an increase in the proportion of the pores and thus a decrease in the density of the dry and this process will continue with increasing humidity to to reach moisture is then the proportion of air spaces as little as possible .If humidity and increased this limit , the trapped air is greater than the effort that fails compaction pressure air trapped or overcome the friction between the grains . And this result will be a reduction in the density of dry soil and an increase in the proportion of the pores and air spaces .And from the above it can be concluded that the pressure in the air spaces Almtwald through scientific compaction is who plays a major role in shaping the curve