THE FACTOR IN THE SETTLEMENT OF A STRUCTURE IS NOT THE AMOUNT OF SETTLEMENT, BUT THE DIFFERENTIAL SETTLEMENT BETWEEN THE DIFFERENT PARTS OF A STRUCTURE ITSELF,NEEDS DESIGN CONSIDERATIONS .

LOAD BEARING CAPACITY OF SOILS:-- The bearing capacity of a soil depends upon the physical characteristics of the soil particles,ie ,size , shape and the cohesive properties frictional resistance and the power to retain moisture etc.moisture content and the changes brought in by the atmospheric influences,heat and rain etc .The finer is the soil particles,the more variables are the cohesive and frictional properties of the soil under field conditions.In general heavier the unit weight of soil is greater the strength and also the lesser the voids ,the greater the strength.With structures built on the sands and the gravels the settlement is likely to be partically, completed at the end of the construction,but when the site is under lain by clays or silts , settlement is likely to continue for a long time after construction and cracks may appear many years after completion.All foundations settle under load and the general tendency is for some parts of a structure to settle more than others causing relative movement.The critical factor in the settlement of a structure is not the amount of settlement but the differential settlement between the different parts of a structure itself.Excessive pressure is comparatively uncommon cause of the settlement.Investigation of all layers under a foundation should be made as even thin layers which are weak in shear can cause settlement.The most marked characteristics of cohesive soils from the Engineering point of view is their susceptibility to slow volume changes .All soils containing greater proportion of clay expand in bulk when wetted and contract on drying the volume changes cause both vertical and horizontal movements of the ground,the vertically movement being generally the more important.Shrinkage and expansion of clay of high liquid limit may be very detrimental.When subjected to load ,even if the pressure is below the maximum safe bearing capacity,some of the contained water is squeezed out with consequent diminution of volume , resulting in consolidation settlement.The possibility of these movements is an important consideration even for light buildings.The behaviour of the clayey soil is most treacherous when in great thicknesses as the total settlement depends on the thickness and the compressibility of the layers .Care is also necessary when the building is on the relatively steep slopes of clay ,since the downhill creep is appreciable and often leads to the serious trouble,as found in the Shimla town and sorroundings during the recent heavy rains affecting bad to worst because of the lapse occured.