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Design of Cantilever Retaining Wall Heel Rebar

Design of Cantilever Retaining Wall Heel Rebar

Design of Cantilever Retaining Wall Heel Rebar

(OP)
I've run across two different methods for designing tension reinforcement in the heel of a reinforced concrete cantilever retaining wall. The methods produce dissimilar designs. Each method considers the heel as a cantilever, with a fixed base at the rear face of the stem. The big difference is how the design moment is calculated; the design moment in "Method A" is calculated using the weight of the heel and soil on the heel acting downward, but neglects the soil bearing pressure acting upward; i.e. the heel has no support from the underlying soil. "Method B" does consider the soil bearing pressure acting upward.

I think it's clear that Method A is more conservative than Method B, but I have been advised that Method A is incorrect. Contrary to the advice I received, I've read that Method A is more appropriate because the reinforcing will be designed to withstand tilting of the wall. I have also seen Method A in older text books.

I'm interested to know if other engineers consider upward soil pressure when they design heel reinforcing. The difference in the design moment is significant, and using Method A will produce a design with more reinforcing steel in the footing top mat.

RE: Design of Cantilever Retaining Wall Heel Rebar

In Basics of Retaining Wall Design, 9th Edition, July 2011, by Hugh Brooks and John P. Nielsen it states numerous times throughout the book that you should ignore the upward soil pressure in designing the heel of the wall footing.

www.PeirceEngineering.com

RE: Design of Cantilever Retaining Wall Heel Rebar

In order to activate the entire weight of the backfill on the to resist overturning, it seems quite reasonable to design the footing for the full weight wihtout "reducing" it for any soil pressure. A fully loaded wall may have footing pressures near the tip of the heel close to zero anyway.

RE: Design of Cantilever Retaining Wall Heel Rebar

I always put in enough top heel steel to develop the overlying soil mass for overturning and shear, otherwise you are just kidding yourself.

I also design the bottom steel per the documented net soil pressure seen.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

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