Pier with vertical rebar drilled and grouted into strong bedrock

[atrizzy]

I'm designing a square pier on a strong granite rock surface. The base of the pier will see overturning and shear forces, that I can easily calculate into the required tension in the reinforcing. My issue is that I don't have a geotechnical colleague available to specify a few of the design parameters. I therefore need to make some conservative assumptions. Below is my intended procedure; am I missing anything?

1. Rebar development within the grouted shaft is simple enough per.

2. The Canadian Foundation Engineering Manual relates the allowable bond stress to "no more than 1/30 the compressive strength of the grout" as well as "not to exceed 1300 kPa." I'll use this in my calculations.

3. I have testing data for the bedrock giving ultimate shear, tension and compression stresses. It is of excellent and unfractured quality. I plan on using an inverted cone method at 30 degrees to calculate overall pullout resistance of the rebar cluster.

Is the above procedure reasonable in your learned opinions?

The other unknown for me is the size of the hole. I would expect that for a 25mm bar I would expect a 50mm hole, if only to allow proper grouting, but this is basically an arbitrary selection on my end.

Any thoughts or advice are appreciated, and thanks in advance.

 

[SlideRuleEra]

I consider your approach reasonable.
For a 25mm bar, 50mm is the minimum diameter hole; you may need to go larger. See the "Five Star Handbook on Grouting & Concrete Repair", excerpt shown below:

http://www.SlideRuleEra.net

 

[atrizzy]

Thanks SRE! Very helpful.