Design of Heel Reinforcement for the Retainin Wall on Rock 1

[aleks25]

I have a tall (30') cantilever concrete wall which is to be founded or rock. Normally, for this type of retaining wall, the heel is designed as a cantilever supporting the weight of the fill and any additional surcharge to account for possible tilting. Is this design requirement still valid for retaining walls on rock.

Thanks.

 

[miecz]

Yes. In order to provide the resitance to overturning about the toe, you'll need to carry this force through the heel.

 

[aleks25]

Thank you, jmiec, I think that answered my question in full.

 

[msquared48]

If you do not or cannot use a heel, you will get into the design of an extremely inefficient "L" shaped retaining wall with the high likelihood of over stressing the soil at the end of the toe. Being founded on rock, if the rock is 10,000 psf or better in bearing, this may not be a problem, just watch out for the required reinforcing and section of the toe.

Mike McCann
McCann Engineering

 

[aleks25]

The problem is actually the opposite - I can not use a toe due to R.O.W. restrictions, so the heel is very long and therefore needs to be very thick and with a lot of reinforcement.

 

[msquared48]

Aah. I misunderstood. Sorry 'bout dat.

Thought about making it a counterfort wall?

Mike McCann
McCann Engineering

 

[aleks25]

It's still one of the options on the table, I'd like to avoid it though. Too much formwork over 450+ feet of wall, which may raise the unit cost and negate any advantage in material savings. The construction time is also quite limited.

 

[msquared48]

OK - try an ecology block wall with a geogrid tieback system.

Or horeizontal concrete walers at 8 to 10 feet anchored back to a series of deadmen.

Both these options would eliminate the need for a large heel.

Mike McCann
McCann Engineering

 

[aleks25]

Thanks for you help, Mike. Unfortunately the client is adamant about keeping the room below the roadway, which is supported by the wall, clear of any possible future utility installations (it's a city street). A modular gravity wall as well as tie-backed walls have already been suggested as a more cost-effective alternative, but regected. So I am pretty much stuck with cantilever wall concept for better or for worse. I'm just trying not to look, for the lack of a better word, stupid when the plans are submitted.

 

[aleks25]

My current plan is that since for walls of that height sliding is usually the controlling factor, design the wall to meet the overturning criteria and use dowels into rock to provide additional sliding resistance. That should give me 2 or 3 feet on heel length and make it thickness more reasonable.