Designing a Foundation

Precautions while designing 'Foundation'

1.  A foundation should be designed to transmit combined dead load, imposed load and wind load to the ground. 
2. Net loading intensity of pressure coming on the soil should not exceed the safe bearing capacity.
3.  Foundation should be designed in such a way that settlement to the ground is limited and uniform under whole of the building to avoid damage to the structure. 
4.  Whole design of the foundation, super structure and characteristics of the ground should be studied to obtain economy in construction work.

Ratio of Cement Concrete and Mortar for Foundation

1.  The cement concrete 1:8:16 is generally used in the foundation of walls in construction work. 
2.  In case of column raft cement concrete 1:4:8 is the best recommended ratio for it in the foundation.  
3.  For brick masonry cement mortar 1:4 to 1:6 is used as loading condition.  

 In case of column and raft footings up to plinth level cement concrete 1:2:4 or 1:1.5:3 are used. 
Soil having Safe Bearing Capacity

Dry coarse and well graded dense sand have maximum shear resistance and maximum bearing capacity. In general submerged soil and clay have less bearing capacity.  

Precautions during Excavation of Foundation Work

The depth and width of foundation should be according to structural design.

1.  The depth of the foundation should not be less than 1 meter in case the design is not available. 
2.  The length, width and depth of excavation should be checked with the help of center line and level marked on the burjis.
3.  The excavated material/ earth should be dumped at a distance of 1 meter from the edges. 
4.  Work should be done on dry soil.  
5.  Arrangement of water pump should be made for pumping out rain water.
6.  The bottom layer of the foundation should be compacted.  
7.  There should be no soft places in foundation due to roots etc.  
8. Any soft/ defective spots should be dug out and be filled with concrete/ hard material