What is pile foundation? Where we need of this type of foundation?
Welcome to Stack Exchange. We could spend an hour writing a lengthy description of Piling Foundations or you could just do some research online.  The answers are there for you, you just have to look.

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Pile Foundations

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This site is for answers to specific questions and your question is really just asking for a broad overview of pile foundations. If after you have done your research and you need something clarified then you can post a SPECIFIC and DETAILED question.