Block, Rebar, Backfill

[Blueboy7]

Since we’re past the footer dilemma, lets move onto the block.
My Garage is going to be 40’ x 40’ 13’6” (21 courses) floor to ceiling. It will be below grade 8’ at the deepest point. It’s all shale with 2 1/2 feet to the bank. Originally I was going to use 8’’ block but I think 10” will be better. Not going to be inspected but I want to do it right.

1. What’s the standard practice with rebar size and spacing, Vertical and Horizontal?
2. And I’m not sure the correct name for it but are pillars needed if you put rebar in the cells?
3. What kind of backfill would you suggest?

As always, thanks for your help!
Blueboy7

 

[lukedwag]

8s or 10s will do fine. Are you anticipating the bank giving way ? There are no real standards per say. But if you did a 4 or 5 bar every 4 feet and grout those cells solid. Put your durawall every 3rd course. More importantly how are you attaching the trusses ?

 

[Blueboy7]

lukedwag I was told the bank will start to push, thats all I know.
I haven't thought much about the trusses, other than using anchor bolts for the top plate 2x then toe nailing the trusses to it.

 

[DougWil]

Since we’re past the footer dilemma, lets move onto the block.
My Garage is going to be 40’ x 40’ 13’6” (21 courses) floor to ceiling. It will be below grade 8’ at the deepest point.

You have a retaining wall. The soil weight acting as a lateral force on that wall is huge.
Both the wall and the footing need to be designed as a retaining wall, sounds like the footing wasn't and you need a drainage system at the footing base to remove any water that will add hydrostatic forces to the wall.

You need to stop and get an engineer to design your wall and footing before you go forward.

 

[csp]

Why block and not a poured foundation? You can form buttresses as part of a poured foundation/stem wall.

 

[theoldwizard1]

Anything built into a hillside has the potential of some serious water intrusion problems.

First you need to divert any uphill water away from your structure. Second, any water that doss come close to you structure need somewhere to go instead of just pooling against your wall. Drainage tile at the bottom and back file with gravel. Landscape cloth between the gravel and any soil.

Block walls are very porous, so if that is what you are going to use, you will need multiple layers of water proofing. A good asphalt based product directly on the block. Then a continuous membrane and finally dimple drain board.

Do it right or you will be doing it over !

 

[Blueboy7]

I'm no engineer but, is it reasonable to think a 10"x20" footer with 2 #4 rebar and 10" block with #5 rebar every 4' or maybe 2' filled with concrete and with durawall every 3rd course and 2 1/2 feet of gravel with drain tile should hold back 8 feet of shale?

 

[xyster101]

I have a 48' long shop built into a hill. It goes from nothing to 7' buried at the back. I did 12" block, rebar ever 4' (2 of them) and then filled the back third. I was going to do a pour every 4' at the rebar, but I bought a truck of cement and had extra, so I just filled as much as I could.
Outside the wall I put water proof plaster on, then tar sealer, then rippled plastic to allow water to drain down the side of the block. I did fabric, #2 stone and drain pipe. Might as well run 2 pipes as pipe is cheap. Then stone up to within 1' of finish grade then dirt.

Here is the plaster applied:

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Then the tar with black plastic dimples over it. Has ben solid for 3 years (knock on wood):

 

[DougWil]

I'm no engineer but, is it reasonable to think a 10"x20" footer with 2 #4 rebar and 10" block with #5 rebar every 4' or maybe 2' filled with concrete and with durawall every 3rd course and 2 1/2 feet of gravel with drain tile should hold back 8 feet of shale?

Your footing isn't near wide enough to act as a retaining wall.

 

[Blueboy7]

xyster101 Nice building. what size is the footer?

Dougwil What would you consider wide enough?

 

[R6 Racer]

To anyone,
If Blueboy7's footer is to small, is there a way to compensate for that within what construction is left to be done?

I'll throw this one out.
Thinking along the lines of a retaining wall, there is an additional poured floor & the 2 side walls of the shop that will help support the "retaining wall" part of the shop.
Would that additional support (they could be the 8's or 10's) along with maybe 12" block on that wall alone, completely filled with concrete & the right amount of rebar, make the structure sound?

Another question. I'll agree to the, there can be a whole lot of weight behind that amount of land statement. And I know different soil types will put different amounts of pressure on a "retaining wall". Where does shale fall in to that factor? Is it a good or bad thing?

Steve

 

[harleybear66]

horizontal poured bond beams?

 

[DougWil]

xyster101 Nice building. what size is the footer?

Dougwil What would you consider wide enough?

Retaining walls have to designed knowing the type of soil, allowable soil pressure, weight and height of soil retained and wall/roof loads acting on that wall.

Also seismic forces of that retained soil act against the wall during an earthquake.

Additionally they can be designed with the footing under the backfill which will help counter overturning.

That is why you need an engineer, hopefully a local one that is familiar with the soil type in your area, to save those investigation costs.

And why no one can tell you how wide a footing you need, or really anything else specific.

I can tell you though that all CMU cells below grade should be grouted solid. Otherwise water can get in the cell, freeze and start breaking your new wall up. Assuming it freezes in winter where you are.

 

[Ironcrow]

I have a block retaining wall. It is 13 feet tall and completely buried, soil to the top. 12 inch block, #5 bar in every other cell, horizontal rebar every 4th course. Every cell grouted full. Footing is 4 feet by 18 inches deep with two sheets of #5 grid 1 foot OC.

Even if you don't have an architect or inspection, this wall is one thing you might want to have an engineer take a look at.

 

[harleybear66]

there are several articles of discussion on the internet the past year or two of backfilling against retaining wall such as this with expanding sprayfoam up to about 6-12 inches of finish grade. this removes some of the tremendious pressure against the wall with heavy rains saturating the soil. this does nothing for waterproofing so the usual steps will still be needed. backfill from the bottom of the wall upward and outward 45 degrees. may be worth an hours time to search the web for info on this

 

[pop pop]

As a retired engineer, I'm always amazed at the eyeball engineering going on in the construction business. You need the services of a structural engineer pronto. You are already in over your head. Don't mean to be curt, but this is serious business when you see failure later. And my guess is where you are headed you'll see it.

 

[Blueboy7]

To anyone,
If Blueboy7's footer is to small, is there a way to compensate for that within what construction is left to be done?

Actually it's not even formed yet.

Footing is 4 feet by 18 inches deep.

And why no one can tell you how wide a footing you need, or really anything else specific.
Assuming it freezes in winter where you are.

Not going to touch this with a 10 foot pole... Yes it freezes here in SW Pa. 32"

there are several articles of discussion on the internet the past year or two of backfilling against retaining wall such as this with expanding sprayfoam up to about 6-12 inches of finish grade. this removes some of the tremendious pressure against the wall with heavy rains saturating the soil. this does nothing for waterproofing so the usual steps will still be needed. backfill from the bottom of the wall upward and outward 45 degrees. may be worth an hours time to search the web for info on this

Actually I planed on spray foaming the outside. Wasn't originally going to angle back the bank, but... Still searching the web on the whole thing.

You need the services of a structural engineer pronto. You are already in over your head. Don't mean to be curt,

Been in constant contact with a friend of mine who does this sort of thing in our area. He's not an engineer but as far as I know the company he works for hasn't had any failures. And I don't get offended with people who are trying to help

 

[xyster101]

I was told to have the footer twice the block thickness. So my 12" cmu sits on a 24" wide footer that is 42" deep with rebar in it.
Also my cmu has a wire grid between layers as full grout too.
My plans I drew were stamped by an architect. I would ask an engineer. It is not so much the dirt to worry about but the hydrostatic pressure of water. Water always wins. Lots of stone and drainage to get that water away from the building.


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