Short Answer:

Pile foundations are deep foundations used to transfer building loads to deeper, stronger soil layers when surface soil is weak. They are long, slender columns made of concrete, steel, or timber driven into the ground to support structures safely and avoid settlement. Pile foundations are commonly used for bridges, high-rise buildings, and water-logged areas.

There are different types of pile foundations based on material, function, and construction method. Major types include end-bearing piles, friction piles, bored piles, driven piles, and composite piles. The selection depends on soil conditions, load requirements, and structural needs.

Detailed Explanation

Types of Pile Foundations

Pile foundations are used when the upper soil layer is too weak or compressible to support the load of a building or structure. Instead of resting on shallow foundations, the load is transferred deep into the ground using piles, which reach stronger soil or rock layers. Piles help in avoiding settlement, increasing stability, and supporting heavy loads.

There are various types of pile foundations, and they are classified based on function, material, and method of installation. Each type is chosen according to the nature of the soil, type of structure, and load characteristics.

1. Based on Function or Load Transfer Mechanism
2. End-Bearing Piles
   These piles transfer the load directly to a strong soil or rock layer at the bottom. The tip of the pile rests on a hard layer, and the entire load passes through the pile to the bottom.

• Used where hard strata are available at a known depth.
• Acts like a column transferring load from top to firm soil or rock.

1. Friction Piles
   These piles transfer the load to the surrounding soil along the full length of the pile through skin friction.

• Used where hard strata is not available at reasonable depth.
• Load is distributed along the surface of the pile.
• Suitable for soft or loose soils.

1. Combination of End Bearing and Friction Piles
   Some piles transfer load through both tip bearing and surface friction. This is common when soil conditions vary and no clear bearing stratum is found.
2. Based on Material Used
3. Concrete Piles

• Can be precast or cast-in-situ.
• Strong and durable.
• Common in modern construction.

1. Steel Piles

• Made of H-sections or pipe sections.
• Used in marine structures and for deep foundations.
• Can be driven easily but are prone to corrosion.

1. Timber Piles

• Used in light structures or temporary works.
• Economical and easy to handle.
• Not suitable in long-term wet conditions unless treated.

1. Composite Piles

• Made using two or more materials (e.g., concrete and steel).
• Used when different soil layers require different material performance.
• For example, concrete in upper part and steel in deeper portion.

3. Based on Construction Method
4. Driven Piles

• Pre-manufactured and driven into the ground using hammers.
• Suitable for all types of soils.
• Immediate load-carrying capacity after installation.

1. Bored or Cast-in-Situ Piles

• A hole is drilled first and then filled with concrete.
• Used where vibration from driving is not permitted.
• Common in urban areas and for large loads.

1. Screw Piles or Helical Piles

• Have helical blades and are rotated into the ground.
• Fast installation and suitable for tension and compression loads.
• Used in light structures, solar farms, and utility supports.

1. Under-Reamed Piles

• A special type of cast-in-situ pile with an enlarged base (bulb).
• Used in expansive soils like black cotton soil.
• Provides good stability by resisting uplift and settlement.

Conclusion

Pile foundations are essential in areas where surface soil is weak or where deep, stable support is required. Different types of pile foundations—such as end-bearing, friction, driven, bored, and composite piles—are selected based on the load type, soil condition, and structural requirement. Proper selection and design of piles ensure safe and stable structures in all ground conditions.