I have came across an interesting type of retaining wall I had never seem before. I found this on a Brazilian book on retaining walls, and the particular feature I am interested in is the "intermediate slab" and shown in the attachment. It appears that the intermediate (or relieving) slab basically "reboots" the laretal earth pressure. I am wondering if anybody has come across this before. The book provided no references and I have not seen this in any geotech book before. Any help with background material or personal experiences would be highly appreciate.
Thanks.

Kind of looks like they moved the "foot" up by H2 with less overfill to restrain the overturning. At first blush - doesn't make a lot of sense to me??

Interesting concept, I have never seen this idea before either. I'm curious what else is on the page as I don't see how d is defined.

It would seem to me that the intermediate slab would have to be very stiff for this to work and therefore would require a lot of steel.

Mike Lambert

The books defines d=h1. It states that this occurs when phi1=alpha=theta=0.
On the previous pages, it defines alpha = slope of the soil above the wall (zero in this case, since it is flat).
phi1 = friction angle of the wall (Coulomb theory) = 0 (doesn't this essentially makes it a Rankine theory?)
Theta = angle between soil-side face of wall and vertical (zero in this case, since wall is flat on the soil side).

Ok that makes sense.

MiketheEngineer - With a gravity wall as shown without the intermediate slab, the backfill doesn't help resist overturning unless you account for friction between the backfill and the wall. So by adding the intermediate slab, they acutally increase the resistance to overturning. Additionally, the method is showing a smaller driving force trying to overturn the wall, this is the interesting part of the concept.

Mike Lambert

It is common in Europe, Russia and South American countries. It is also referred to as a retaining wall with relieving slab(s). By installing these slabs, you break the linear active earth pressure and this results in much smaller moment at the bottom of the stem. Therefore less stem reinforcement and not as wide a heel slab. There is a good coverage of this type of retaining wall in F.D.C. Henry's 1986 text, Foundation Design and Construction.

Makes sense, but the 'relieving' slab adds quite a bit of $ in construction costs. Since formwork costs more than just about anything else I am not sure it makes much sense from strictly a $ standpoint

Thanks for the help.

Maybe to avoid the formwork it is done in two stages. Pour the wall up to the bottom of the slab. Backfill and pour the upper section. It would work best with a long wall.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.