Conc Ret Wall on Rock, w/ embed rebar dowels, procedure?

[BurgoEng]

I would like some input onto the procedure I am going with to figure out this situation. And also because I know this will come up again on other projects. Thanks in advance...

Situation: 8ft concrete retaining wall in which rock has been encountered at a shallow depth. Footing width was initially about 8ft wide (1ft toe) but due to presence of rock, I'm being asked to re-evaluate wall to limit amount of rock needed to be excavated, i.e. reducing footing width and using grouted rebar into rock to resist Overturning, Sliding, etc...

My Plan: Calculate OT Moment. Say, B = width of footing. I am assuming to have rebar at 1ft clearance from end of heal. Tension capacity req'd assumed to be
T(req'd)=M/(B-1'). Rebar capacity in tension is about
T(rebar)=0.4 fy As.

My problems: What is shear capacity of rebar? How do I calc capacity of grouted rebar in rock, i.e. what would the bond stength be per foot of embedment (assume w/c ration of 0.4 grout)? Do I need to have the eccentricity of moment limited to e<=B/6 for bearing capacity check? or no need to because of using embedded rebar so there is no need to avoid tension in soil?

 

[cvg]

you need a geotech / geologist to give you rock strength or recommended design value for the rock anchors before you can complete the analysis. I would recommend a key trench excavated into the rock to prevent the footing from sliding.

 

[SolidPE]

Burgo:
Your approach is reasonable. Things to look for- getting down to sound, relatively flat(6H:1V) rock. Don't worry about the resultant in the kern- as you said, the bars will take the tension.
For some guidance on designing the dowels or rock anchors, look at Williams Bar Rock Anchors.. They show the theory and some reasonable assumptions for bond strength.
Finally, although a key in the rock would work, it would more economical to install extra dowels to take the horiz load in shear friction. This would also engage the lower portions of the rock which would tend to be less weathered and more structurally sound. (say, #5 bars 18" deep grouted in with hydraulic cement in a 1 in dia hole). Hope this helps.