CMU RETAINING WALL 1

[surjaan]

I designed a retaining wall with #7 bars vertical , but contractor used # 5 bars. The bottom of wall (about 16") is over stressed. Instead of demolishing the wall, I was thinking of adding 2 courses of 8" blocks at the base making the wall 16" at the base and vertical dowel into the footing and horizontal dowels into wall with epoxy. Foundation is OK. Any suggestions

 

[ToadJones]

How about adding some Pilasters?

 

[surjaan]

I think it will be more economical to add another 16" high CMU wall or concrete wall & dowel it to existing. Because past 16" above base wall and reinforcing is OK.

 

[JLNJ]

The trick is going to be making the scabbed onto stem act as a single unit. I don't know if I could convince myself that enough shear bewteen the surfaces would be activated to make this happen.

 

[surjaan]

What if the they can take out the interior face of CMU wall for bottom portion and pour 16" concrete wall against the existing with dowels.

 

[msquared48]

Just a comment here:

#7 bars in an 8" CMU wall seems a bit much. I try to restrict it to #6's or go to a thicker wall. Must be a high wall, and/or highly loaded.

At this point, I think, depending on the horizontal steel used in the wall, adding interior pilasters would be the cheapest alternative. These do not necessarily have to be CMU. They could be steel.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[concretemasonry]

The one solution that jumps to me is that the drawings and specifications are followed.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[bylar]

Depending on your horizontal steel and the site conditions have you given any thought to putting deadmen in and tie the top of the wall to the deadmen?

 

[BAretired]

If you add blocks to the exterior face (compression face) then you would need to bond the new block to the existing in order to develop a greater effective depth for the #5 bars.

But you are proposing to add blocks to the interior face (tension face) where the effective depth of the existing bars will be unchanged.

I may not be interpreting your description accurately. Could you provide a cross section showing the proposed remedial measures?

BA

 

[rscassar]

The one solution that jumps to me is that the drawings and specifications are followed.

The vertical steel in the reinforcing wall should have been inspected prior to grouting. This not only ensures that the correct reinforcing has been used but that it is located on the correct face for a cantilevered retaining wall (earth retaining face).

I have detailed a 16" x 16" pilaster doweled into the cmu wall before.

 

[lsmfse]

We have used a concrete auxillary wall on the tension face. You could use dowel pins to transfer the shear. Also you need to design the walls to be integral, possibly some connection at the top of the proposed auxillary wall and the existing construction. Has the wall been grouted yet?

 

[surjaan]

Thanks for your suggestions.
Grout in CMU wall is not filled yet. I may suggest him to add CMU pilaster for additional support. Contractor can dowel in to slab, however do you have suggestions how he can connect pilaster to CMU blocks which are already in place.
Thanks again

 

[lsmfse]

Knock some holes in the face shells of the block and use ties between the two.

 

[concretemasonry]

The added ties to the added wythe must be sufficient and spaced properly to take advantage of the possible added flexural strength of the added wythe of masonry.

Possibly, a closer look at the loads and assumptions would be be a an alternate to determine what is controlling, since the designed wall may really be acceptable with the materials used.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[hokie66]

Since the wall is not yet filled, the solution is simple as lsmfse said. Just knock out the face shells on the compression side, use "C" or "E" blocks for the extra wythe, and fill the whole thing. Use some ties and dowels if you want, but not really required. I would make the added width 3 courses high.

 

[csd72]

I have desined these things before as a propped cantilever which exerts a point load on the additional stub at the bottom. That way all you need is a point load capacity rather than longitudinal shear.

 

[BAretired]

Adding blocks on the compression side would be a good solution structurally, but it may not be acceptable aesthetically.

BA

 

[Bobber1]

Backfill behind the wall with a lean concrete mix. Place it slowly so it doesn't overload the wall. When it sets up, no more lateral pressure. You can make it lean enough to be "digable" by hand and it will still be strong enough to exert no lateral force.

However, you can still get water between the fill and the wall and you may have to drain this unless your wall can take the hydraulic pressure.

Bob G.

 

[hokie66]

BA,
I interpreted interior to be compression side, but I guess the OP never made that clear. I wouldn't depend on drilled in bars on the tension face to make it work.

Bobber1,
Your solution doesn't eliminate lateral pressure, it just tends to make the wall act as a gravity wall rather than as a cantilever wall.