Concrete Footers?

[HotRod]

I'm building a retaining wall in Southern, Ontario were the winters can be "a lot of fun" and I need to know how deep I need to make my footers so that the wall is not going to shift with frost? Also this is what I plan on doing I'd like suggestions and any other help that can be provided.

I plan on digging footers 4 feet into the ground and creating them with concrete. On to of the footer "wall" I will be laying recycled concrete that is old sidewalk this will be laid and mortared together just like any other stone wall. So my questions are?

1) When building such a wall should I be using rebar to hold everything together? 2) Can anyone recommend a website or other documents that will show me how to lay and mortar a wall? 3) What is considered good technique? 4) How deep should the footers be? I figure the wall will be roughly 12" thick

[DanG]

I do not understand all your needs. I think I would be much more inclined to look at a "garden wall" design. Rather than pouring a

4 or 5 foot footing and creating the drainage and rigidity to have a real retaining wall, I would look pretty hard at no footing, gravel base, free stacked rubble concrete retaining wall that lets the hydrostatic pressure go through the wall rather than trying to stop it.

Look up "garden wall". Look up Keystone block. Look up "broken concrete" retaining wall. Here is an example:

(top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) [e-mail]

[Goedjn]

The footers should be below the frost line. You don't say how high this retaining wall is supposed to be, or what it's supposed to be retaining. If it's less than 3' high, and you don't expect to trap water/ice behind it, and you're not parking a vehicle closer to it than it is high, then you probably don't need rebar.

Depending on what the thing is for, you might look at doing a revetment, instead of a vertical wall.

[Pat Coghlan]

Your wall sounds like it's rigid. If it cracks, there goes its strength.

You're better off (structurally and aesthetically) to buy a block-type product, which will only require an 12" aggregate base. The blocks interlock and will last forever.

-Pat

HotRod wrote:

[HotRod]

SORRY for not being clear the retaining wall is going behind the house (Walkout basement) , it is holding the dirt back on the one side of the house that also has a gravel driveway to my shop. So the dirt height will slope from about 6' to nothing. The retaining wall height will be 8' for the whole length. I've done a lot of reading about hydrostatic pressure and plan on putting a final plan together for a concrete engineer (friend) to review before I build anything. My friend mostly deals in roads and bridges so a retaining wall is something he hasn't had to touch. When I pour the footers I plan on leaving 1/2 pipe at 16" spaces through the concrete as I don't care if it holds back water.

[HotRod]

Sorry it doesn't interest me a bit, if I wanted to do this the easiest way possible I would have been done a month ago. This is about recycling materials and making it look nice. The whole deck will be made out of recycled beams and concrete. I'll post pictures when I'm finished. BUT now back to the issues.

You're better off (structurally and aesthetically) to buy a block-type product, which will only require an 12" aggregate base. The blocks interlock and will last forever.

-Pat

HotRod wrote: I'm building a retaining wall in Southern, Ontario were the winters can be "a lot of fun" and I need to know how deep I need to make my footers so that the wall is not going to shift with frost? Also this is what I plan on doing I'd like suggestions and any other help that can be provided.

I plan on digging footers 4 feet into the ground and creating them with concrete. On to of the footer "wall" I will be laying recycled concrete that is old sidewalk this will be laid and mortared together just like any other stone wall. So my questions are?

1) When building such a wall should I be using rebar to hold everything together? 2) Can anyone recommend a website or other documents that will show me how to lay and mortar a wall? 3) What is considered good technique? 4) How deep should the footers be? I figure the wall will be roughly 12" thick

[Michael Daly]

How high is the water table? You won't have to worry about hydrostatic pressure - the soil should drain. The soil pressure on the other hand should be considered. If you're looking at an 8' high wall that's vertical, you are likely to need rebar - especially if there's ever going to be somehting on the soil above the wall - it isn't clear where the wall is relative to your driveway - is it above the wall?

If your friend is a real engineer (presumably civil since he works on roads and bridges), he can figure it out for you. BTW - there aren't many bridges that don't have a retaining wall at the abutments.

Mike

[HotRod]

My friends a busy guy and until I do some leg work myself I'd hate to ask him to do it for me. The driveway leading to the shop will be held back by the retaining wall. The truck will be driving roughly 4 feet away from the wall. The retaining wall will be 8' from backyard level but the retaining wall will slope from about 6' to nothing. Now that I think about it I wonder if maybe I should tie the rebar into the house foundation? I've done a bunch of reading and just want to make sure that what I have planed is going to work before the backhoe comes in and digs my footers.

[Goedjn]

If the driveway is up top, and the wall is 8' high, then I wouldn't use an unreinforced rubble-wall. You DEFINATELY don't want to attach the retaining wall to the house. If the wall is sufficient by itself, then it's un-necessary, and it it's not, it will rip a chunk out of your cellar when it fails.

If I understand, what you're trying to do is what's in the sketch labled "simple" at

Depending on how much space you've got, for an 8' wall, I would either add pillasters, which are stiffening ribs, space about every 4', or lean the entire wall into the slope. This latter is almost guaranteed to produce cracking, but the cracks don't matter as much, because the dirt holds the wall up while the wall holds the dirt up.

In any case, 8' is pretty high for a retaining wall, so you definately want some iron in there.

One munipality discusses retaining walls here:

Note that walls that are taller than people are really serious business, as are walls that are holding up driveways. Build this like a classical roman. Overbuild the shit out of it.

--goedjn

[EXT]

Look at the specifications and installation drawings for the manufactured stacked bock type of retaining walls to see what they use/recommend for a wall that high. Not to buy the stuff but to learn from it. From what I see, an 8 foot tall wall, only 1 foot thick, with a driveway load on top will suffer from early failure. You need your engineer friend to do some real design work. Probably you will need to make it about 4 feet thick at the bottom, use Geo-textile for reinforcement every couple of feet and then I am not sure because broken concrete will not stack in a rigid manner for such a tall wall with that load.