Retaining of road

[Matt]

Hi,

I would like to retain a 20' high x 30'long section of private road. If I used caissons what would be the diameter, steel, and height to depth ratio spaced at 6'o.c.. I plan to pour an 8" minimum reinforced wall between columns to retain the dirt.

Regards
Russ

[webmaster]

Hello Russ,

Thank you for your question.

This is a very interesting problem. As I understood from your question, you are planning to pour a caisson structure (foundation slab, walls and top slab) to retain an already existing private road. First of all, let me advise you that the caisson solution (usually utilized for underpasses or drain gutters) may be more expensive than a usual concrete retaining wall but I do agree that such depths should require to construct your structure with concrete.

If you want to stick to a caisson solution and be on the safe side, I would at least consider a steel bar diameter of 0.4" at every 6' center to center. Steel mesh for quick installation with at least 16' overlap between them and well executed steel connections to the foundation slab reinforcement.

Of course this is a preliminary assessment but I did assumed a worst load case with bad soil conditions without water and a square caisson design, so the above seems to be safe enough.

Hope this helps,

Regards

[Matt]

Hi,

I wanted to used concrete caissons with rebar formed in sonotubes. What do you think the diameter of the tube should be? Depth into soil? Size and quantity of rebar in tube. Thanks

Russ

[webmaster]

Russ,

Sonotubes for foundation of footings are quite frequently used in the US, compared to Europe. This is nevertheless a good method but requires special efforts during pouring of concrete. Check if a concrete mixing truck will be able to reverse near enough to the holes and ask them for special longer chutes to pour directly in the holes.

My suggestion would be (from experience):

-Sonotube say ID=18"
-Hole depths minimum 48" for frost footing depth
-6 x Rebar minimum dia.0.4" per sonotube at 6' center to center held with stirrups
-Sonotube to be poured at least 6" above grade.
-Sonotubes to be places at relatively short distances depending on footing reinforcement and thickness.

Hope this helps you further.

Good day,

Best Regards

[Matt]

Thanks, that really cleared things up and I really appreciate your timelyness response.

I will buy you some wine.

Russ