VARIATIONS OF THE MOISTURE CONTENT CHANGE THE VALUES OF THE ANGLE OF REPOSE , THE AMOUNT OF COMPACTION REQUIRED, AND THE COHESIVE STRENGTH OF THE SOIL .

The properties of a soil mixture are influenced more by variation in the moisture content than by any other cause.Saturated soils are improved in strength by the drainage and the dry soil loose strength by saturation.A water logged ground is undesirable because of its low bearing capacity.Fine gained (clayey) soils are most likely to suffer by water absorption .It is therefore important to ascertain the wettest condition in a given case and the basis of design should be the strength of the wet soil .Clayey soils are subject to a large amount of shrinkage but the loss of water that causes this shrinkage is slow , and the shrinkage might amount to as much as twenty percent in volume .In the case of sandy soils the detrimental effect of moisture is much less than clayey soils.Granular soils do not hold water readily and do not shrink much when drying but they shrink more rapidly.When such soils are saturated with water and the water is trapped, the footing may be supported on hydraulic pressure.Under such conditions the soil is without shearing strength.The seepage out of this entrapped water will cause settlement, therefore this water must be drained out .A rise in the Ground water level may reduce the safe bearing capacity of soils , and lowering of the ground water over an area may result in differential settlement of structures .The water logged strata below the surface of the underground reservoir of water is said to constitute the zone of saturation,the surface of water is known as the water-table and the level at which the water table occurs is known as the standing water level or ground water level.In areas where considerable seasonal changes in moisture content occur, the resulting volume changes in clay sub grades can be minimised to some extent by rolling in granular materials.The moisture content of a soil is defined as the ratio of the weight of the water present in the soil to the dry weight of the solid soil particles and is expressed as a percentage of the solid particles .A condition which may be roughly just bind together when squeeze hard in the hand defined as optimum and the optimum moisture content is that at which a specified amount of compaction will produce the maximum dry density in the soil and it is expressed as a percentage by weight of the dry soil.For sand and gravel the OMC generally occurs at about 8to 10 percent, which may be at 15 percent for silts , and 15 to 20 percent for clays . Variations of the moisture content change the values of the angle of repose , the amount of compaction required and the cohesive strength of a soil .