huangyhg

how can i do this, 7/8 or 1" rebar embedded in rock?
i am building 3 ft high 12" thick wall on rock. i excavated the top 12 inches of highly weathered rock and top soil; now i have a solid place for the footing. because the wall will be a potential impact wall i want to resist overturn. i am planning to place 12" diameter and 3 ft deep piers @ 10 ft o.c. a chain-link fence post will also be embedded in the piers as well. in between the piers i am planning to drill 3" diameter holes and embed a 7/8 or 1" re-bar also 3 ft deep @ 2 ft o.c. the re-bar will extend vertically to the whole wall height and the horizontal re-bar will tie to it. is the 3" hole filled with cement grout enough protection for the re-bar from rusting?
sounds like it should work based on the limited details. and if you are drilling in to rock, i suspect the 3" hole will be fine. i've seen much smaller holes used where hard rock was encountered and epoxied the rebar in place.
wow, i don't think that wall is going anywhere. i'd use coated rebar to resist rusting.
i would go with a smaller hole and use epoxy. drilling is easier and the rebar will be protected by the epoxy. a #7 rebar would require only a 1 inch or 1-1/8 inch hole, which can be drilled with a hammerdrill instead of a wet coring drill which would be required for the 3 inch hole.
i agree with ron. too large a hole in the 24" spacing could tend to spall or split the rock matrix, depending on the condition. moreover, the amount of grout or epoxy will be excessive. 1/8" to 1/4" clearance all around is all you need. you might also consider staggering the holes by a couple of inches if possible to decrease the chance of splitting the rock, depending on the overturning requirements.

mike mccann
mmc engineering
i would use a pneumatic rock drill with a 32mm bit and then epoxy grout. the only corrosion issue might be the joint between the rock and the concrete. if the surface is rough and looks like a good bond can be achieved then it should be fine. any particular corrosion concerns such as salt water?

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