Digging around 12' pier

[WWTEng]

Consider a 3'x12' deep pier foundation supporting an out door structural column. The contact tor was supposed to pour a pipe within the concrete. The contractor forgot to do that. They are recommending digging down to one side of the pile 9' deep to install the pipe and fill the void with grout.

I am not a huge fan of this approach. I think once the native soil is removed, the skin friction will be difficult to replicate with the grout. I also don't understand the "dig to one side" of the pile. I think it would be impossible to not cave in the soil on other sides.

I think I should have them remove and replace with a bigger pile.

Any thoughts?

Thank you.

 

[JAE]

I don't think you will have much skin friction capacity in 12 feet in any case.

Usually you ignore the top 5 feet for skin friction. Are you sure this is a friction pier? With a 3 ft. diameter I'd be inclined to think this is end bearing only.

Now if the pier is also resisting lateral loads (which I doubt at 12 ft. depth) there might be a concern but backfilling in well compacted lifts or with flowable fill might be OK.

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[BridgeSmith]

As long as the pier isn't laterally loaded when they excavate and the "grout" backfill is flowable enough to fill the voids in the soil and along the shaft, it shouldn't be detrimental to the capacity.

 

[JoelTXCive]

How big is the structural column on top? And how tall is it? What sort of loads are we dealing with?

Maybe there is room to pour a cap on top of the pier? If you have room between the top of the pier and bottom of whatever the structure is, then maybe there is room for a cap?

You can chip out the top portion of the pier to expose rebar, or dowels to achieve development length perhaps.