Compaction question

[premierjax]

Hey guys finally starting my build of a 60x36x12. I will be putting in the 6x6s this next week. I have a 2' drop from one end to the next and have been bringing in fill this past week. Ill be putting down 6"-8" at a time and then using a plate compactor on it before putting another 6"-8" down. My question is if Im putting my posts 4' in the ground, do I need to go actually 6' in the 2' filled area so Im going 4' into undisturbed soil, or will the compaction make it good enough so I would be roughly 2' into undisturbed and 2' into fill. I will be pouring a 4" mono slab with about 1' outer edges set on top of the concrete for the post. Any thoughts would be appreciated.

 

[Desertwndrr]

I don't do anything without direction from my soils engineer. Everything that I do is done according to their firms recommendations and signed off by them. I also only hire the most conservative firm in the area. Why? Because I have personally seen way too many lawsuits and destroyed homes in the area here. I will not ever purchase a lot without first talking to my engineer and I will not ever purchase a lot that is questionable.

Your question assumes that the undisturbed soil is good to use in its current state. Way too many variables to give you a hard and fast answer. Pay the money and hire somebody good to review your site and project.

 

[r22yu]

I would go with the proper depth for your piles. Compacted soil won't add strength to the bearing capacity of your piles, they need the depth. If you put them in too shallow you also risk pushing up the ground around the pile.

 

[premierjax]

If I put them say 6' down and then backfill Ill that much gap between the footers and the slab. I planned on having the outer edges of the slab sitting on top of the concrete poured on the post, is this correct thinking?

 

[6768rogues]

You want the posts on undisturbed soil. If going 4 feet down puts them in 2 feet of fill and 2 feet of undisturbed soil, it is ok. Undisturbed soil is to mitigate settling, 4 feet of cover is to mitigate frost damage. Fill works fine for frost prevention.
That said, the size and design of the pad you place in the hole to bear the weight depends on the soil type and its weight bearing characteristics. For example, clay soils are not good for weight bearing because they become squishy and might require a larger footing. Gravelly soil holds much more weight. For a barn, ballpark estimates usually work.
6 inch lifts is good for compaction. There will still be a little long term settling even though you compacted it because you will probably not get more than 95% compaction. That is usually acceptable, but is not 100%.

 

[theoldwizard1]

You have to check with the local building inspector for local codes. Some places require a 6-12" "cookie" to be poured into the bottom of the hole. This has to set for a prescribed amount of time before putting a post on top. Back filling the post and hole may require sand, gravel or cement. It all depends on local codes.

Personally, I would set the posts first, backfill them and then add fill. Keep you lifts to 6" maximum.

 

[premierjax]

You have to check with the local building inspector for local codes. Some places require a 6-12" "cookie" to be poured into the bottom of the hole. This has to set for a prescribed amount of time before putting a post on top. Back filling the post and hole may require sand, gravel or cement. It all depends on local codes.

Personally, I would set the posts first, backfill them and then add fill. Keep you lifts to 6" maximum.

I was trying to build this without giving the damn city $350. I figured a 2'x4' or 5' hole will beat any kind of cookie I would place. My thought for filling first was so that I could pour each post to the level exactly 1' below my finished floor, so when I pour my slab it will rest on all posts evenly

 

[Mike in Ohio]

I am a little confused, I did the same thing on mine but had a little more than 3 feet to bring up in one corner. I brought the fill which was pretty heavy clay type soil in about 6" at a time and compacted with a plate compactor. In the low corner I buried my 6x6 5' deep so it was 2' into undisturbed soil. The county required that my post holes be 18" in diameter with 12" of concrete under the posts. The posts were set on the concrete and backfilled with the soil that came out of the postholes. The rest of the building was put up and the concrete floor was poured last. After 6 years not one crack in the floor, nor any settling that I can see.

Setting treated post in concrete is a no-no around here. When I worked at the lumber yard they said it voided the warranty.

I don't understand what you mean my "pour each post 1" below the floor"

 

[premierjax]

I am a little confused, I did the same thing on mine but had a little more than 3 feet to bring up in one corner. I brought the fill which was pretty heavy clay type soil in about 6" at a time and compacted with a plate compactor. In the low corner I buried my 6x6 5' deep so it was 2' into undisturbed soil. The county required that my post holes be 18" in diameter with 12" of concrete under the posts. The posts were set on the concrete and backfilled with the soil that came out of the postholes. The rest of the building was put up and the concrete floor was poured last. After 6 years not one crack in the floor, nor any settling that I can see.

Setting treated post in concrete is a no-no around here. When I worked at the lumber yard they said it voided the warranty.

I don't understand what you mean my "pour each post 1" below the floor"

Hey Mike I'll be digging my holes 2'wide and 5' deep, so I can set the poles and fill with concrete up to the 4' mark leaving 1' for the downturn of my outer edges of the slab. That way the slab will set right on top of the concrete I poured in the holes.

 

[Mike in Ohio]

Hey Mike I'll be digging my holes 2'wide and 5' deep, so I can set the poles and fill with concrete up to the 4' mark leaving 1' for the downturn of my outer edges of the slab. That way the slab will set right on top of the concrete I poured in the holes.

Ok I see what you mean now, you still may want to check about filling the post hole with concrete. It may void the warranty on the treated wooden posts.

Where are located?

 

[brownbagg]

the bldg won't settle due to the natural ground of the piling but the slab will crack due to settlement of fill, also a plate tamp is worthless, it doesn't put out enough energy to compact more than 2 inches of sand at a time

 

[premierjax]

brownbag, I talked to the local guy that makes the metal trusses for these setups. I walked around his property he had a 32x60x12 a 50x100x12 and a 24x30x12 all on the same type soil Im on, and built the same way Im going to do mine. He said he used a roller for his but he would feel good about using a plate compactor as long as I did each lift at 6"

 

[cyamaha2007]

I wouldnt back fill the post with concrete. We put chat around the post and compact as you fill.

 

[premierjax]

Hey guys the fill Im getting is pretty clean but it does have a few roots, am I wrong in thinking as long as I pack this to where there is no voids or air around the roots they shouldnt rot right?

 

[larry_g]

I got dinged by the inspector here for not having the holes 4' deep below undisturbed soil, fill did not count. We were also required to pour a pad in the bottom of the hole and to fill around the post with concrete. Our county is now doing aerial inspections and if buildings show up that weren't there the last time then expect a visit. You may skirt the permit process now but you may get caught and If I were you I'd make sure that you have all your ducks in a row if you have to defend your engineering in the future.

Hey guys the fill Im getting is pretty clean but it does have a few roots, am I wrong in thinking as long as I pack this to where there is no voids or air around the roots they shouldnt rot right?

Your organic material will rot and leave voids in the ground. I would accept no organic material.

lg
no neat sig line

 

[premierjax]

larry how do I find fill without organic material? Any of the trucks around here deliver fill from whatever pit they can find. When I mean roots its not packed full there is a root every now and again. When Im grading it out with the boxblade every maybe 5 -10 min Ill see a small root come up. I spoke with the guy thats bringing it today and he said its what he gives all his builders, he is the one that said as long as its packed right and there are no voids I wont have any issues

 

[Theminiroberts]

Any Screened Clean Fill shouldn't have organic big enough to make any difference/

 

[walrus]

larry how do I find fill without organic material? Any of the trucks around here deliver fill from whatever pit they can find. When I mean roots its not packed full there is a root every now and again. When Im grading it out with the boxblade every maybe 5 -10 min Ill see a small root come up. I spoke with the guy thats bringing it today and he said its what he gives all his builders, he is the one that said as long as its packed right and there are no voids I wont have any issues

Sounds you are getting bank run gravel, never seen roots in screened gravel. How big are the roots? I wouldn't worry much about it if they are small in diameter, nor would I worry if they are few and far between

 

[premierjax]

walrus, Its not gravel just fill dirt. The roots cant be but maybe 1"-2", but like I said out of 5 loads so far only 3 roots were 2" round and 2' long the rest are 1" and smaller.