Foundation/Footing and Its Types (Deep)

B) Deep Foundation

 This is preferred where the soil strata at the surface are not very good. The foundation is driven deep into the ground till it reaches a hard strata or compacted soil. Deep foundation can be classified as;

1. Pile foundation 

 Piles are generally used in buildings. Piles are driven into the ground to strengthen the strength of the soil below. 

According to their use they can be classified as,

•  Bearing pile
•  Friction pile
•  Sheet pile
•  Anchor pile
•  Compaction pile
•  Fender pile
•  Batter pile

According to the material used, piles are classified as;

a. Timber piles

b. Concrete piles i. Precast        ii. Cast- in-situ

c. Steel piles

d. Composite piles

2. Well foundation

This foundation is mostly used in black cotton soil which is good for agriculture & bad for structure. This type of soil has high shrinkage value due to change in moisture content and volume varies as 20-30% of original volume. It develops very wide & deep cracks due to excessive shrinkage and is problematic for foundation.

Precaution for foundation in black cotton soil 

•  Foundation depth be enough below from cracks to hard strata
• Prevent foundation from direct contact with black cotton soil
• If thickness of black cotton soil is high,foundation is to be laid on piles
• Raft foundation is the choice in this condition
• Tie-beam in plinth is important

Bearing capacity of soil

It is the ability of soil to support the load coming over it. Bearing capacity of soil depends upon the types of soil.

Methods of improving bearing capacity of the soil

1. Compacting the soil
2. Increasing depth of the foundation
3. Drainage of soil
4. Grouting 
5. Chemical treatment
6. Driving sand piles

Some Common Problem with existing foundation

1. Causes of foundation settlement
2. Consolidation of soil particles
3. Reduction of moisture content
4. General earth movement

Effects of unequal settlement

• Distortion of structure fabrics
• Failure of structure

Prevention of undue unequal settlement

• Proper foundation design
• Proper soil investigation

Causes of foundation failure

• Unequal settlement of sub-soil
• Unequal load distribution
• Horizontal movement of soil adjoining structure
• Lateral pressure tending overturn
• Shrinkage due to withdrawal of moisture from soil
• Atmospheric action
• Lateral escape of soil below foundation
• Nearby building construction
• Trees etc.