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Timber Pile Mess Up - Can I Replace?

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  • Timber Pile Mess Up - Can I Replace?

    Hi all, my name is Steve. I build single family homes in coastal NJ. First time posting, happy to be here, and hoping that someone here has some experience with a problem I'm having on a work in progress:

    The house is being built on 10" treated timber pilings. The piling contractor set the band beams about 1' too low and subsequently cut off the tops of the piles. The initial remediation plan was to pull the pilings out of the ground and reinsert new pilings. The piling contractor stated that this has happened, though rarely, in the past. No problem.

    However, our engineer, who consulted with two geotechnical engineers, has stated in no uncertain terms that this is bad idea. Due to the soil now being disturbed, according to her, we will not be able to attain the friction capacity necessary to maintain the integrity of the pile - even if we can achieve bearing ("toe") capacity.

    I spoke with a separate geotech who thinks it's fine. My research online has been inconclusive with the exception of a blurb in the IRC about pulling out and replacing damaged piles (suggesting that this is an acceptable practice). I also read that the displacement caused by driving the piles increases the surrounding density thereby increasing the piles' capacity.

    The soil is sandy and cohesionless as far as I know. To me, it stands to reason that, within a short amount of time, the soil will redistribute and be suitable for reinsertion.

    Any chance anyone out there has had a similar experience? Success? Failures? Suggestions? Thanks in advance

  • #2
    Steve, welcome to the forum. I don't have any experience with piles and only have one customer with a house built on wood piles. Her deceased husband was an architect and designed/built the house in the mid '80s. Did the engineer have a solution to offer? Deeper or larger diameter piles? Somehow extending the existing ones?



    • #3
      Hi Steve, thanks for the reply. So, we've actually come back around to pulling the pilings and replacing them with new pilings. The following may get long but I found it interesting so I'll share in case it helps someone else. We did consider enlarging the pile diameter, in the end it proved unnecessary.

      The soil on the project is basically a water and sand mixture. In geotech speak this is course, cohesionless, sandy gravel. In effect, as soon as the piles are pulled out the soil will immediately begin to settle back into place. As opposed to clayey soil which would leave a void.

      Another factor is that timber piles are "displacement type" pilings which mean that they are driven into the soil, displacing it as it penetrates, thereby increasing the density of soil around the piling.

      Finally, there is a phenomenon called "pile set-up" that occurs especially fast in this type of soil. As the pile is driven in it pushes away the pore water (water between granules); as that pore water settles back around the pile it increases the overall capacity of the pile. This "set-up" factor increases the overall capacity by as much as 2-fold. However, it is rarely taken into account when the foundation is design; in effect, the piles are already "over-engineered" for the application.

      Taking all of these factors into consideration, all parties involved were made comfortable with the prospect of pulling/replacing.


      • #4
        I have only seen this footing on TV shows. Do not know if it is practiced anywhere in Missouri unless it would be on some island in the middle of a river or along the river. I know that they pile drive some I beams in places but always assumed they were heading towards bedrock and not just sitting on more sand/gravel mix.

        What I don't understand is how they remain stable when we seem to hear about rising sea levels, when storms like Super Storm Sandy come along and wash away parts of the beach. And what type of wood pilings are you using> You talk about a sand/gravel mix with water so how do you keep the pilings from rotting out or even sinking more?


        • #5
          I have built over 200 homes and countless decks on pilings. I wouldn't have any problem pulling the pilings and reinstalling them, but NOT in the the same locations.
          I would want to move them at least 2' in any direction, or if this is not possible then use 5' longer pilings. You can recheck the bearing capacity by waiting 24 to 48 hours and trying drive them deeper.Usually the friction wil have increased by then.