Brief overview of pile foundation

A concrete pile belongs to mainly a long cylinder in reinforced concrete covered in the ground to provide a consistent support for the structures which are required to be constructed on top of a platform supported with one or more of stated cylinders. The set is described as foundation piles or deep foundations.

Pile foundations are very effective for high buildings since the design loads are very immense which can’t be borne by spread footings. Erstwhile, when the soil contains low SBC or the soil is cloggy, a raft or a pile foundation is the best choice.

Piles are categorized as follow :-

1. The way in which the load is transmitted to the soil.
2. Method of Installation.
3. Material of construction.

Categorization of piles on the basis of load transfer

Point Bearing Piles: If bedrock or hard strata exists inside proper depth, piles are expanded to be supported on the bedrock or infiltrate necessary depth into the hard strata. Under this situation, the final bearing strength of the pile is completely based on the elementary rock/strata.

Friction Piles: In a friction pile, the load on pile is mostly obstructed with skin friction along the pile shaft. Pure friction piles are likely to be longer as compared to point bearing piles.

Resistance refers to a function of the shaft area adjacent to the soil. In cohesion-less soils, like sands of medium to low density, friction piles are frequently utilized to raise soil density. When there are no hard strata at proper depth, end bearing piles are not recommended as they can increase cost. Piles are pushed through the softer material to desired depth toward this type of subsoil condition.

Steel piles: These are mostly found in marine and other structures. Maximum length is basically infinite. They contain relatively larger load capacity.

Benefits: Larger capacity, is ideal for end bearing for various reasons like easy to splice, small displacement, capacity to penetrate through light obstructions.

Drawbacks

• Safeguard for the metal against erosion is necessary
• There is possibility for being damaged/deflected with major obstruction

Concrete Piles

• Concrete piles come in the form of precast, pre-stressed, cast in place, or composite construction.
• Precast concrete piles are formed with ordinary reinforcement or pre-stressed steel.

• Precast piles with ordinary reinforcement are developed to withstand bending stresses throughout transport as well as bending moments from lateral loads and arrange adequate resistance against vertical loads and any tension forces which may create at the time of driving.
• Pre-stressed piles are created by tensioning high strength steel pre-stressed cables. Generally, there exist higher-strength concrete (M35 to M55) in pre-stressed piles due to the large initial compressive stresses caused by pre-stressing. Pre-stressing the piles, likely to neutralize any tensile stresses throughout handling or driving.
• Max length: 10 - 15 m for precast, 20 - 30 m for pre-stressed
• Optimum length 10 - 12 m for precast. 18 - 25m pre-stressed

Benefits

1. Ability to deal with High load.
2. Corrosion resistance is possible with cathodic protection; sacrificial anodes or impressed current method.
3. Hard driving is feasible
4. Cast in place concrete piles are developed by drilling a hole in the ground & filling it with concrete. The hole is drilled or created with driving a shell or casing into the ground.

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