Retaining wall footing attaching to bedrock

[dm3415]

I have a 20' concrete retaining wall I've designed and is being constructed. The contractor is hitting what he thinks is bedrock (most likely it is) near the obviously large footings for the wall. He wants to tie in to the bedrock in lieu of getting all the rock (most likely granite and basalt) out of keyway and heel of the footing.

I know to look for cracking in the rock to be greater than 3' apart and to verify competent rock. I'm planning on coming up with a drilled epoxy dowel schedule to incorporate the footing to the rock, beyond that I'm not sure, has anyone had experience with this situation?

 

[msucog]

who's tasked with evaluating bearing pressure for the footing? get them (the geotech) to look at it and offer their thoughts.

if it's competant, mass rock, i've seen some folks spec drilling and epoxying rebar in to the rock. for relatively small walls, i've seen it spec'd drilled 6-8" in the rock and spaced 6"-12" along wall. it depends on the design and reinforcement.

20' tall wall is pretty large so i'd suggest putting your head together with the geotech to come up with a solution.

 

[dm3415]

Fortunately he's down the hall from me and we're going to inspect it next week. Thanks for the input.

 

[fattdad]

Then again you could build the wall and post-tension into the rock.

f-d

¡papá gordo ain’t no madre flaca!

 

[kslee1000]

Some thinkings:

1. Make sure he has reached "Bed Rock", not a huge boulder, which may complicate your solution.
2. What is the water table? Any consideration on potential corrosion on the epoxy dowels? Will the wall still stable if dowels are gone?

 

[msquared48]

As a corollary to msucog's comment, make sure you stagger the dowels as you do not want to have so many so close that the rock matrix is compromised from the drilling.

Again - ask the geotech...

Mike McCann
MMC Engineering

 

[csd72]

I have speced this and it is actually fairly common in the Sandstone in Sydney.

Analyse like a concrete beam or steel base plate design with the bearing pressure as limited by the geotech.

 

[dm3415]

csd72-
So, like a beam on elastic foundation analysis, with really high soil modulus values in lieu of the rock pressures? Thanks