Most of the time a SRW is chosen for it's flexible benefits, which also can save on cost compared to masonry. You remove these benefits by placing they system over a rigid footer. Are you building the wall over excavated soils or fill? There are other ways to stabilize the subsoil rather than concrete.

 

Well, Alanblock will tell to NEVER do it. But I did it at My own house. I'll get pics tomorrow.
Also,call. Allenblock for help. My dealer will just about print you a set of plans if you buy their block.

 

Why use a flexible wall system with an inflexible base?

That said, sure why not.

 

I think concrete will work, maybe overkill though...Just excavate out all the loose soil and compact some clean 3/4" stone with a layer of geotech fabric. That will more than likely handle it don't you think?

 

superseal -

A segmental retaining wall (SRW) on a rigid concrete footing would not be overkill, but it is UNDERKILL since it cannot perform as designed can fail in many ways. - That is about a dumb as using Type S or M mortar when Type N is what is needed for the job.

I have seen SRW walls up to 40' high and no had concrete footings because the major licensers/developers (Allan, Anchor, Keystone and VersaLok) will not accept that problem since they have done all the research and gotten local, national and international code approvals for a SYSTEM.

They not not buy the geo-grid myth, but recommend well graded and compacted base material (not clean rock). They do recommend geo-grid for walls over 4' or 5' (depending on local codes) that need to be engineered.

 

They do recommend geo-grid for walls over 4' or 5' (depending on local codes) that need to be engineered.

even a 2' tall wall could require grid, depending on surcharges or other conditions. I would also build up with compacted lifts of clean stone in an overdig situation, the final lift would be modified though.

 

Leave it to the engineer to keep us in line... :laughing:

Should be modified base although our local 3/4" packs very well.

GeoFab is still a friend though/ soil stabilizing and such.

 

The situation at my own home was that the builder ,25 years ago, built a low retaining wall out of boulders to retain the driveway. The wall is about 4' high. Problem is, is that the driveway is 4'-5' above that and had a steep slope off to the side. So rather than remove the boulder wall, I poured a leveling cap and laid Allenblock on top. There is a lot of steel in the cap and the base course is pinned every 4' or so. The rest was laid by the book with attention to back fill and geogrid.
10 years so far and not the lightest sign of movement.

BUT, I will be the 1st to say that putting a concrete footing under an Allenblock wall is WRONG! :laughing: :laughing:

 

Thank you for all your replies!

So what would you guys think is the major causes of SRW's sinking?

Is it improper drainage? not enough 3/4" base?

The wall i am building will be just over 4'. I will be installing a drainage pipe and geo grid.

Any other good rules of thumb/tips when it comes to preparing the base?

 

Here's some shade tree engineering for ya. My driveway. 1st course laid in mortar on reinforced concrete leveling pad. :whistling

Like I said. 10 years absolutely no movement. Bit of a surcharge also. That's where my 9000 lb truck parks every night.

 

Incorrect installation is 100% the cause, because a correct installation will not fail, ipso facto.

The most common incorrect installation detail is the base, followed by the drainage, then a lack of engineering, especially on tiered walls or walls with a surcharge (e.g. the ground is not level at the top of the wall).

 

This is taken from A December 1995 Newsletter by Allan Block:

Is a poured concrete base required when building Allan
Block Retaining Walls?
No!​

In most cases a poured concrete base reduces the built-in flexibility and drainage
present in a properly constructed Allan Block retaining wall. A well graded, compatible
aggregate base, installed following Allan Block specifications, provides the best foundation. Generally, walls under four feet high need a base 4 inches thick by 24 inches wide. Walls over four feet high require a minimum base of 6 inches deep by 24 inches wide.

This fact has not changed. Check it out for yourself:
http://www.allanblock.com/RetainingWalls/Newsletter/olderversions/Advn1295B.pdf​

 

The block only moves because the base was inadequate, so the cause is soil settlement. - That us obvious to anyone.

A rigid poured concrete footing looks fine initially before and immediately after completion, but once Mother Nature starts her daily/seasonal or regional variations and frost heaves, it can be a determent. A segmental wall (SRW) is used because it can adapt to the extremes and return without cracks. It also provides some well needed drainage even if the wrong soil is used as a backfill.

 

If the soil does not look good to you you can call a Geotech to look at it and do testing. We have in the past as per the job specific conditions and per the Geotech have overdu 2' deep below the 6" leveling course by 4' wide installed 2 1/2" clean stone wrapped in filter fabric and then installed 6" of 3/4" clean stone for our leveling base. You can also use a flowable fill.

 

Thanks for all the replies and ideas.

Ive decided to just use 8" of 3/4" clear crush as my base.

Another question though, does it matter if i bury the drain pipe in the leveling base? or can i put it behind the first course of allan block?

 

Thanks for all the replies and ideas.

Ive decided to just use 8" of 3/4" clear crush as my base.

If by "clear crush" you mean stone w/o fines, I wouldn't recommend it. You'd just be inviting water to bypass the drainage outlets and migrate to the subsoil, creating even more problems for the wall. Use non-pervious gravel under the wall, and behind the wall to at least as high as finished grade on the exposed wall side.

Another question though, does it matter if i bury the drain pipe in the leveling base? or can i put it behind the first course of allan block?

As Captain stated, it has to be above grade on the finished side of the wall or it won't be draining anything.

 

You will actually want that behind the second course of block.... Seeing as how the first course will be burried in the base. They have tech specs for this on their site I would think.

 

a few months later...

So this is the result of you guy's awesome tips and answers:


https://www.facebook.com/media/set/?set=a.320099288019446.98577.252420448120664&type=1

Thanks everyone