Details of pile and well foundations

Deep Foundation is categorized as (a) Pile Foundation, (b) Well Foundation

(a) Pile Foundation: When the soil strata adjacent to the surface of the earth is weak and fails to sustain the load of the super-structure, the load should be transmitted to the hard strata at the deeper depths via piles or well foundations.

Pile supports the structure by procuring the strength in two ways :

i) Friction of the surface of shaft with the soil and ii) End bearing support to pile.

Bearing strength of a pile refers to the minimum load at which a pile proceeds to sink devoid of any further increase in the load, it is known as the ultimate bearing strength of the pile. A pile can bear the safe load and it is based on the factors :-

(a) Ultimate bearing strength divided by some appropriate factor of safety.
(b) Allowable settlement.
(c) Complete strength of the pile.

The piles are categorized on the basis of the following factors:

(a) Categorization on the basis of the functionality of the piles:

(i) End Bearing Piles: In these types of piles the load is transmitted to the hard strata via the end of the pile. The soil in the interim is soft and loose.
(ii) Friction Piles: In these types of piles, the load is transmitted to the soil via friction along the surface of the pile.
(iii) Compaction Piles: The compaction piles are employed if the loose granular soil is compacted to raise the bearing capacity.

(iv) Tension Piles: The piles are utilized to anchor down the structures (where uplift forces operate) and sustain the tension. They are known as tension piles.
(v) Anchor Piles: Anchor piles are arranged to give anchor support against any horizontal pull.
(vi) Batter Piles: The objective of these types of piles is to withstand any horizontal or inclined pull because of moving ships etc.
(vii) Fender Piles and dolphins: These piles are built up to safeguard the water front structures against the moving ships or floating objects.

(b) On the basis of installation process, the piles are categorized as follow :

(i) Pre-cast driven piles
(ii) Driven cast-in-situ piles
(iii) Bored cast-in-situ piles

(c) On the basis of material applied, the piles are classified as follow :

(i) Concrete Piles
- Precast driven piles
- cast- in-situ piles
- pre-tested concrete piles

(ii) Timber Piles

(iii) Composite Piles
- Concrete and Timber Piles
- Concrete and steel piles

Well Foundations: The depth of the well foundation is dependent on the following factors

(i) The well should be provided underneath scour depth and it is known as grip length
(ii) The well should be dived to adequate depth in order to meet the requirement of bearing strength.