Introduction

Foundations are that part of a structure, which transmits the load of the whole structure in to soil below ground level. For a 9 inch wall the width of foundation requires is 2.25 feet or 27 inch. Country burnt bricks can be used for walls of 9 inch is sufficient for a 2 storeyed villa. English or Flemish bond shall be adopted. For one bricks these have equal strength. If the load increases the area that is the width must be increased not the depth.

Selection of type of foundation

By definition shallow foundation depth of foundation is less than or equal to width otherwise it is called deep. Mainly bearing capacity and settlement is studied. Secondly cost is to be low. Condition of soil is taken into consideration. Foundations of the neighboring structures, is observed.

When the bearing capacity is low area of spread footing is large then we can suggest mat or Raft foundation. It is not economical except in labor and speed of work. Soil testing must be done. From standard penetration test values, the N values bearing capacity is found. Settlement is observed. Shear strength and consistency shall be found for cohesive soils and clays settlement is a factor.

Spread footing is economical it does not need any special skill or equipments. Engineer must be know middle third rule to avoid tension at the base.

Depth of footings

For Villas if the soil is hard Random Rubble Masonry is economical and safe. It is continues and width is adjusted accordance with bearing capacity. It is good not to lay PCC, because if PCC is given there is a chance for tilting. Offset for basement and wall shall be given after studying earth pressure and reaction. Sizing for spread footing is done for punching shear and bending moment calculation. In a site if the soil is loose for one portion lay PCC to that portion only. If organic matter is present remove it.  I have an experience in this case. PCC can be given at top with a light reinforcements.

Conclusion

To spread the load in an area the loading capacity of soil is not to exceed the safe limit, this is the main objective of the foundation. Too much height of basement is not good. We must be careful about geometrical stability, even though an attraction of stars and planets is a matter.