PILE FOUNDATIONS

CLASSIFICATION OF PILES

Piles may be classified in a number of ways based on different criteria:

(a) Function or action
(b) Composition and material
(c) Installation

Classification Based on Function or Action

Piles may be classified as follows based on the function or action:

End-bearing piles

Used to transfer load through the pile tip to a suitable bearing stratum, passing soft soil or

water.

Friction piles

Used to transfer loads to a depth in a frictional material by means of skin friction along the

surface area of the pile.

Tension or uplift piles

Used to anchor structures subjected to uplift due to hydrostatic pressure or to overturning

moment due to horizontal forces.

Compaction piles

Used to compact loose granular soils in order to increase the bearing capacity. Since they are

not required to carry any load, the material may not be required to be strong; in fact, sand may

be used to form the pile. The pile tube, driven to compact the soil, is gradually taken out and

sand is filled in its place thus forming a ‘sand pile’.

Anchor piles

Used to provide anchorage against horizontal pull from sheetpiling or water.

Fender piles

Used to protect water-front structures against impact from ships or other floating objects.

Sheet piles

Commonly used as bulkheads, or cut-offs to reduce seepage and uplift in hydraulic structures.

Batter piles

Used to resist horizontal and inclined forces, especially in water front structures.

Laterally-loaded piles

Used to support retaining walls, bridges, dams, and wharves and as fenders for harbour construction.

Classification Based on Material and Composition

Piles may be classified as follows based on material and composition:

Timber piles

These are made of timber of sound quality. Length may be up to about 8 m; splicing is adopted

for greater lengths. Diameter may be from 30 to 40 cm. Timber piles perform well either in

fully dry condition or submerged condition. Alternate wet and dry conditions reduce the life of

a timber pile; to overcome this, creosoting is adopted. Maximum design load is about 250 kN.

Steel piles

These are usually H-piles (rolled H-shape), pipe piles, or sheet piles (rolled sections of regular

shapes). They may carry loads up to 1000 kN or more.

Concrete piles

These may be ‘precast’ or ‘cast-in-situ’. Precast piles are reinforced to withstand handling

stresses. They require space for casting and storage, more time to cure and heavy equipment

for handling and driving.

Cast-in-situ piles are installed by pre-excavation, thus eliminating vibration due to driving

and handling. The common types are Raymond pile, Mac Arthur pile and Franki pile.

Composite piles

These may be made of either concrete and timber or concrete and steel. These are considered

suitable when the upper part of the pile is to project above the water table. Lower portion may

be of untreated timber and the upper portion of concrete. Otherwise, the lower portion may be

of steel and the upper one of concrete.

Classification Based on Method of Installation

Piles may also be classified as follows based on the method of installation:

Driven piles

Timber, steel, or precast concrete piles may be driven into position either vertically or at an

inclination. If inclined they are termed ‘batter’ or ‘raking’ piles. Pile hammers and pile-driving

equipment are used for driving piles.

Cast-in-situ piles

Only concrete piles can be cast-in-situ. Holes are drilled and these are filled with concrete.

These may be straight-bored piles or may be ‘under-reamed’ with one or more bulbs at intervals.

Reinforcements may be used according to the requirements.

Driven and cast-in-situ piles

This is a combination of both types. Casing or shell may be used. The Franki pile falls in this

category.