Pile Foundation

If the piles go to bedrock, one 600mm pile would have about 12.5% more cross-sectional area than two 400mm piles. But if the piles are friction piles, two 400mm piles would have about 33% more vertical surface area than one 600mm pile. Your consultant seems to be considering the second condition.

I am not familiar with the Chennai area but in many areas in coastal India you end up driving the pile to a hard layer of sand - bedrock is a bit elusive along much of the coastal area there - friction grip.

The consultant should have test pile data or he is simply making a wild assed guess - that can get expensive.

It sounds like at least three of us are on the same page....

To make an informed suggestion based on the limited input would be impossible to do. Suggesting that you use something other then your consultants suggestions, would also be bad engineering practices.

You need to consult the engineering firm your working with. As I assume they have all of the geological data for you area. Along with any government regulation that would need to be followed as well. OR as I am reading into your question, someone else who you might have more confidence in.

In India no one is going to court in the event of a screw up - not worth the twenty years it would take to get the case to trial.

They need a good consultant - one that is not related to the owner or any senior managers.

Yes, you can use one pile per column if the applied loads are within the allowable. However, I don't think one pile will be able to support the load of a column of a nine story building. The pile must be checked for all loading conditions. Earthquake and wind loads put a lateral load on the piles and that must be considered for the bending in the pile and the lateral soil pressure. Remember, there is a reduction factor for piles in a group. This foundation design requires a competent structural engineer. One pile per column is meaningless. All loads from the building to the foundation must be considered. Also, as an added note, don't forget to check the wind load on the diagonal of the building as well as the square faces.

The design of the foundation is much more complex than just using the pile vertical load allowable.

Have some fun today,

PAPADOC

Hi there

Your Pile consultant / designer is, most certainly considering friction piles as this is Chenai - and he seems to be right. Dont bother to increase the size of piles and decrease the numbers - Its not gonna help you and neither it will save money. By the words "Connecting all piles" if you mean strip beams on grade connecting all Pile-Caps then you will do that anyway for integrity of the foundation system as per Chennai Municipal requirements.

Either way you are not gonna save much. Look at the soil test report - highlight the advised Cement Type-4 or Type-5? SRS or CRS? Those are the points where you can save something more than meddling with the consultant's design of Piles or Pile-Caps or even Grade-beams connecting the Pile-Caps.