pier

[astidham]

Hello all,
here is how im going to build my piers, please tell me what you think.
Im goint to drill 36" deep 12" diameter.
dig the bottom 12" out to 24" diameter and fill that 12" with crusher run gravel, and tamp it in.
attach a PT 2x12 to the bottom of a PT #2 6x6 post to place on top of the tamped crusher run.
back fill hole to grade with crusher run gravel.
paint the lower 18" of the post with tar and build up area around the post with dirt dug from hole so water runs away from it.

[Redoverfarm]

Hello all,
here is how im going to build my piers, please tell me what you think.
Im goint to drill 36" deep 12" diameter.
dig the bottom 12" out to 24" diameter and fill that 12" with crusher run gravel, and tamp it in.
attach a PT 2x12 to the bottom of a PT #2 6x6 post to place on top of the tamped crusher run.
back fill hole to grade with crusher run gravel.
paint the lower 18" of the post with tar and build up area around the post with dirt dug from hole so water runs away from it.

I really don't think you will accomplish anything with this step other than weaken the surrounding soil which could cause the post to move laterally.  This would be the right approach similar to a big foot concrete footing but IMO not for a gravel footing. A better approach would be to lay a 12"X12" solid block, paver or to pour 3-4" of concrete in the 12" diam to give more footing to the post and allow the surrounding soil to go undisturbed.  Maybe others might have additional thoughts but that's my $.02 worth

[diyfrank]

You may want to  give more information such as location and soil type. What you intend to build.. whether there will be inspections.

[astidham]

clay soil, 20x30 single story.
soil dont seem to get wet under about 10".
no inspections, permit is required but they do not give any info on foundations

[MountainDon]

I hate clay.   What do the houses in your area use. Or more succinctly, what are the older homes that are still sitting upright with no problems sitting on for a foundation.   

Also, you state the soil seems dry(drier) after 10 inches depth. Over what period of time? Years? Is this a usual, normal state or a dry period?

[astidham]

Hey MountainDon,
most houses in this area are 5-6 years old on a slab,
their are some older cabins in the area on skids.
The soil is so thick and hard water doesnt seep very deep.
it has been very wet, i had a shop built in december and the dirt i had moved for the shop is dry about 4" down. i know this because i planted some cactus yesterday

[astidham]

here are pictures of my shop,



the fron side hill where the swing door is, is where i planted plants

[astidham]

would backfilling with dirt be more sturdy?

[MountainDon]

I don't know enough about clay and building on clay soils to recommend.  

If the "normal" thing with your soil is that it's only the upper 10" or so that ever gets wet then I wonder if packing around the piers with crushed rock is a good idea. Is that going to move the water down further into the soil to where it will upset the "balance" of the deeper soil? I'm out of my element when it comes to the mechanics of clay soils.

As for the PT piers and foot plate, the best type for this has more of the preservative than that for the usual ground contact type. The 0.60 pcf material is rated for use in ground or fresh (non salt) water.




I know I hate the stuff (clay) when I get stuck in it.  

[John Raabe]

I don't like clay either and recommend the pier foundations for well drained gravely soils. You should not use them in high wind or earthquake areas either. That said, clay soils can be a problem for any other type of foundation too.

If the soil is dense and has a high bearing capacity your strategy should work. The sharp gravel "big foot" that you describe will work if the soil won't "mush-out" at the bottom. However a lot of water running down the hole making the clay at the bottom wet and slippery could defeat the strategy. A poured footer with a cast in place post anchor would provide better uplift protection (wind, etc) and not be as subject to wet soil problems.

[astidham]

Thank you Guys