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I've got a wraparound porch on the house. It's supported by a half dozen 28" x 30" x 24" concrete piers (plus other sized concrete piers elsewhere) along the front of the house. They're all floating on the ground at the top of a fairly steep slope, pushed back 6-7' or so from the edge. Everything is in good condition. Not seeing any cracks, etc.

However, the ground under the corner pier has eroded because of a bad drainage problem -- poorly directed downspout (fix in progress) -- and the front edge of the block isn't supported anymore. It's starting to settle and causing the post to move. The porch has a bit of a bounce to it now in that corner, but I don't think it's moved any.

The angle is a bit exaggerated in the picture.

Sinking

Sinking 2

Sinking 3

(Note: lattice is not attached to post)

I would like to remove the one concrete block and replace it by digging out a proper footing and putting in a longer post. I'm envisioning something along the lines of a 3-4 foot sonotube sitting on a 6" footer (bit of a WAG on that).

The ground is rocky clay and it would be on a bit of a slope.

Is this the right sort of solution or am I just just going to introduce more problems in the long run?

  • I wouldn't want to "waste" the existing block. I would add a short concrete block retaining wall (Keystone or Vers-a-Lok units or smaller) around the base and then fill and compact around the base of the porch support. If necessary, then shim between the block and the porch beam to re-establish the original slope of the porch. – Jim Stewart Apr 17 '17 at 19:45
  • @JimStewart I'd be concerned that the retaining wall would need to be fairly deep to handle the slope? – Steve Apr 17 '17 at 21:27
  • Good point. If there is a slope, a floating support will eventually slide because if the soil is loaded it will eventually slump. Keystone or Vers-a-lok units lock together with pins, but the bottom course would have to be buried 8 inches or even 12 inches. Overall this might not be as long lasting as a piling that goes down 2' or 3' to rock. But I would try to fix what you have first before going to a replacement. Walls of VersaLok or Keystone compact units (~>40 lb each) are extremely resistant to sliding. – Jim Stewart Apr 17 '17 at 22:17
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I would endeavor to keep the pier but "fix" it.

First would be to get the pier block back into its original, ideal position. Probably this can be done DIY with a car jack, a bunch of scrap lumber, shovel, and a helper to muscle the block out of the way, dig/fill appropriately, then replace the block.

Then drive some mini-pilings in front to help hold its position even as the ground wanders away. If you can rent a jackhammer (or vibratory hammer or pneumatic hammer), you can probably install the mini-pilings yourself.

  • Rig up a platform for the jack so it can relieve all weight from the pier block and restore the deck position. It is probably expedient to raise the deck another inch or two above ideal position to provide adequate working space re-inserting the pier.

  • With all weight off the pier block, move it out of the way.

  • Rework the underlying soil so it will support the pier block as it was originally. Probably you'll have to remove the sagged material and add gravel to rebuild its support.

  • Put the pier block back into position and test it by temporarily jacking down the deck, let the block bear the weight, jump on the deck a few times, and inspect. Repeat until satisfactory.

  • Remove the jack and its platform, and install mini-pilings according to instructions. Note that it is very difficult to pull out a piling if it is not positioned correctly. Set up ABS or PVC pipe with braces as a guide to starting each.


Having all the foundation be the same design is superior because as the earth moves is the best chance of the deck moving in the same direction at the same time. Using different foundation technologies will cause the deck to travel in different directions.

  • I'm not opposed to keeping the existing pier, but it weighs nearly a ton (1500 lbs) and I don't imagine it'll be easy to move. – Steve Apr 18 '17 at 17:24
  • @Steve: What kind of fun would it be if it were easy? You can use an engine hoist, block and tackle, shop jack, cables tied to vehicles, etc. The block is 11.66 cubic feet or 1/3 cubic metre: that should be about 700 kg which is 1540 pounds. Instead of being an hour project, it might be three days, but having it done well is worth it. – wallyk Apr 18 '17 at 19:29
  • No argument on doing it right. I just don't wanna move a 1500 lb block of solid concrete. ;) – Steve Apr 18 '17 at 20:46
  • @Steve: Perhaps it is sufficient to tip the block rather than move it? – wallyk Apr 18 '17 at 21:18
  • Maybe. It's only moved an inch or so, so it doesn't have far to go. Might just need some good leverage. – Steve Apr 18 '17 at 21:56

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