Pile Spacing - As measured from unused piles

[Serhiy2]

Good day,

I'm dealing with building addition for which I'm using friction cast in place piles. Existing overhead crane structure piles are also present on site and some of these piles will be abandoned. The geotechnical report calls for spacing new piles at 3 diameters apart. My question is if this 3 diameter pile spacing needs to be maintained as measured from abandoned piles?

 

[oldestguy]

Ask the geotech the question. We only have a small bit of what goes on.

 

[BridgeSmith]

The spacing requirements are to prevent overlapping of the soil resistance zones (double dipping by attempting to use the same soil to resist loads from multiple piles). In the AASHTO spec, you can have piles closer than 3 diameters, but there's a reduction factor based on the spacing to account for for the overlap. If the "abandoned" aren't carrying load at the same time as the new piles, then they're just harder areas of the surrounding soil. Why would that have any effect on the piles you're loading? (Other than maybe adding some resistance)

 

[EireChch]

Agree with HR, if they are cut down below pile cap then it doesnt matter, they are likely adding resistance. If they were considered in the final pile foundation design they are working piles and should be spaced as per the recommendations. But as OG said -as your geotech.