Piles in Construction

Pile Foundations

• Piles are used for foundations of structures like transmission towers and offshore platforms that are subjected to uplift.
• Piles are used to transfer the load below the active zone in expansive soils like black cotton soil that swell or shrink with water content changes.
• Piles are required when soil conditions are prone to washout, erosion, or scour underneath shallow foundations.

Classification of Piles

• Piles are classified according to materials used, mode of load transfer, method of installation, and use.
• Materials used: timber, steel, concrete, and composite piles.

Timber Piles

• Timber piles are made from tree trunks, trimmed of branches, and designed for a maximum load of 15 to 25 tons/pile.
• Additional strength can be obtained by bolting fish plates to the sides.
• Timber piles last for about 30 years and are used for structures with moderate loads and temporary structures.
• Breadth of timber piles ranges from 12 to 16 inches.

Advantages of Timber Piles

• Low cost per running length of the pile.
• Suitable for impact absorption due to timber's resilience.
• Easy to install and uninstall if necessary.

Disadvantages of Timber Piles

• Small bearing capacity.
• Untreated timber piles above groundwater may last more than 25 years but are not permanent.
• Prone to damage by hard driving.

Concrete Piles

• Can be pre-cast or cast in-situ, and are generally reinforced.
• Driven cast-in-situ concrete piles are constructed by driving a permanent pile casing, followed by reinforcement and concrete pouring.

Bored Piles

• Constructed by boring through overlying soils to find a bedrock strata or remain in the soil to act as shaft friction and end-bearing piles.
• Piles are designed to resist axial compressive loads.
• Construction involves rotary drill rigs, temporary casing, and bentonite for unstable subsoil conditions.

Screw Piles

• Equipped with internal grout pipes extending downwardly through the tubular pile shaft.
• Grout pipes connect with side-opening ports in the shaft side wall to inject fluid grout into the surrounding ground.
• Pile length is restricted depending on the mode of transportation available.

Steel Piles

• Have a large bearing capacity and can penetrate through stiff layers or boulders.
• Less soil displacement during driving.
• Can withstand rough handling.

Disadvantages of Steel Piles

• High possibility of damage from corrosion and electrolysis.
• Relatively expensive unless the bearing stratum can develop large pile capacity.
• Less effective than friction piles.

Composite Piles

• Made by driving two different materials one over the other to achieve economy in piling work.

Mode of Load Transfer

• End-bearing piles transmit the load through the bottom tips to a firm stratum below.
• Friction piles transfer the load through skin friction between the embedded surface and surrounding soil.

Classification by Method of Installation

• Driven piles
• Driven and cast-in-situ piles
• Bored and cast-in-situ piles
• Screw piles
• Jacked piles