Post-Grout Anchor Diameter

[InDepth]

What is the maximum anchor drill diameter one can post-grout for a tieback anchor? i.e. can you post-grout a 12" diameter drilled hole? What is typically feasible? Any good references?

 

[Erdbau]

Call one of the tieback specialty contractors (Nicholson, Hayward-Baker, etc.) and talk to them about it. Those guys are usually glad to talk with you. I've found their advice helpful on a few occasions because they bring up practical considerations that may not have been apparent.

What are the soil conditions/loads/number of strands? 12 inch diameter seems large. If these are going to be cased holes, casing over, say, 5 to 6 inches in diameter becomes much more difficult for the drillers to handle and load. This translates into more expensive tiebacks.

 

[born2drill]

I've successfully regrouted 7" tiebacks in the past, but I've never tried anything larger. That's also about the practical limit where men can still handle the drill casing by hand.

Erdbau is right - 12" is huge for a tieback drill hole. I would be concerned about the grouting pressures required to crack a grout column that large.
I second his questions - what design loads are you trying to achieve and what are the subsurface conditions like?

 

[wedlmic]

SWP used regroutable anchor systems exstensively - 8" was pretty much the practical limit - probably in the industry. The soil surrounding the anchor has some limiting effects. Handling a five strand anchor is not fun. 12" IS HUGE - how many strands / bars? Is this a vertical application (tiedown) or horizontal anchor? Yes you can fracture a 12" grout bulb - but not with conventional grout tubes and methods. Secondary "special" grout tubes would need to be used. You sould consult with a specialty contractor to see if some value engineering can be done to reduce costs and improve constructability without loss of performance.

Wedlmic

 

[InDepth]

Thanks for the input so far. Here is a table I found in the california Shoring and Trenching manual that I found helpful.