RETAINING WALL STABILITY 1

[Tstruct]

I need opinions on stability of the retaining wall (see attached file). Soil is hard rock which could not be excavated by an excavator. So client wants to move the retaining wall up (as shown in the attached file). Previously, retaining wall was supposed to be placed below the lower road level. I need opinions on potential problems in this placement as both ground and foundation are exposed. Thanks

 

[Once20036]

Looks to me like there's nothing to resist sliding.

 

[kipfoot]

No geotech I've ever met would consider rock exposed to elements and weathering to be adequate for the long term bearing of that toe. Nor sign off on the shear capacity of the rock resisting the key.

I think a different type of wall system might be worth looking into.

 

[HTURKAK]

Shift the shear nib to the end of heel and provide a min. 2 ft separation btw. toe of the RW and exposed rock vertical surface.

Say my opinion ..



Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[Aesur]

Concerns include sliding resistance, global stability of the soil, would need geotechnical approval and capacities as well (which as kipfoot said, most likely won't happen). Can you move the retaining wall outside the bench to drop it back to original depth?

 

[Tstruct]

@Once20036 what is your observation about shear key not being enough to resist sliding, please explain.

I have seen other threads too where people aren't fond of shear key to resist sliding. This is my first time dealing with shear keys. I would really like to know about if they aren't sufficient against sliding.

@kipfoot this is what I am mainly thinking about.

@HTURKAK Road's right of way is an issue, maybe I should design it without toe and keep that 2ft buffer. By the way, that toe is 2ft in length.

Thank you everyone for your valuable comments.

 

[haynewp]

I would make the ftg wider if possible before proposing a shear key into rock.

 

[Tomfh]

Move the key further back.

 

[Once20036]

Tstruct:
If we ignore the people who aren't fond of shear keys - What do your calculations say about horizontal stability? The passive pressure in front of a retaining wall footing to resist sliding increases with depth. Think about 200 psf/ft as a triangular load. Your shear key only appears to be a foot or two deep and I think it's unlikely that any substantial force can be developed in that depth.

Visually speaking, the heel of the retaining wall doesn't appear (to me) to be sufficiently large to collect enough weight that friction would be used to provide horizontal stability.

Even if the numbers worked out on one of those two methods, I`d still be concerned about a geotechnical failure. I think all the classic equations that we know and love assume an immense amount of soil (rock). In your case, all of your horizontal forces could fail through the vertical rock face shown in your sketch.