WHY THE MAT FOUNDATION IS PROVIDED WHERE THE BEARING CAPACITY OF SOIL IS CONSIDERED LOW .

MAT FOUNDATION :-- A mat foundation is provided where the bearing capacity of soil is low so that considerable area of the footing is required and the total area of footing required is generally more than fifty percent of the area of the building. Mat foundations are provided where distribution of pressure on the whole area is possible as in the case of clayey soils.In case of the stiff soil the load will be distributed on smaller areas round about the column and the mat will not be effective .In case columns are spaced uniformly and carry equal loads the mat foundation can be looked as series of continues combined footings in two directions ,and the load is carried in the two directions ,a reduction factor for bending moment and shear force may be used.The reduction factor will depend upon the layout of the columns and will vary from 15 to 30 percent.Beam and slab system of mat foundation is preferred when the area is extensive and the load coming on the columns may be different or spacing of the columns is different and there is possibility of differential settlement.To avoid cracks due to shrinkage, small area are constructed at a time and construction joints are located at places of low shear stress, generally along the centre lines between the columns .The adjecent strips are filled after after 24 hours .The reinforcing bars should be continues across the joints .The concrete should be strong at the joints to transfer the shear .The section may be thickened at the joints , if necessary.