I have a need for information on Helical anchors. They are used for settling or sinking foundations. They are used to jack it back into position and support it. Sold under names such “Chance” and by a company called “Ram Jack” to name a few. Do they work– or junk science? Is there a better time tested method? Not cheap so I am looking for supportive evidence hopefully from someone who used them and doesn’t install them. Thanks.
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There was a story in FHB #104 about using what they called helical piers to rescue a sagging house. The link is to the magazine index page.
http://www.taunton.com/cgi-bin/artresult-fh.cgi?heading=Helical+piers
Yeap, they work. I don't sell them, but when I've needed them for my own projects, I've welded them up on site.
Utility companies have been using them for 40 or 50 years to secure the guylines for transmission poles. Construction appications have increased in the last 20 years for foundations, foundation jacking, retaining walls and such. A small, light anchor, installed with moderate torque provides tremendous tensile or compressive strength. The guidelines for most of the commercially available ones are that the tensile strength tens times (ranges around 9 to 12) the torque. I realize that's apples and oranges, i.e. the units don't match. But if the torque meter shows 700 foot-pounds during installation, then you've got 7,000 pounds of tensile (pull-out) strength. For small ones I use around the house (for a 41-degree beach-access stairways, for instance), I've just used two big homping pipe wrenchs and two high school footall players. The big boys use backhoes and excavators to run a hydraulic square-drive head.
I would guess the soil has to be pretty much rock free for these to work, no?
We're about to try them on a site that probably has a fair amount of rock. I'll let you know how it works out.
DRC
Doesn't work in rock. Within soils, gravels would be okay. Coarse gravels and smaller cobbles would be okay if they are smaller that the pitch of the auger. (The auger come in many different size, usually selected for needed strenght, but could be selected for soil type. Larger cobbles or boulders - nope.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Can you refer me to any documentation on this, maybe on the web? I'd sure like to take it to the architect and the engineer before we break ground (rather than after we break these piers or the budget).
Thanks Much,
DRC