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Deadman Anchor Design - With Uplift

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Bodgy Engineer

Bodgy Engineer

Structural
Mar 7, 2022
13
Picture1_emimwy.png
Hi,

I'm trying to design Deadman guy anchors, with significant uplift, and horizontal force.

A typical arrangement for a guyed dead anchor is to bury a concrete block at depth, then protrude an anchor rod to the ground line (this obviously causes a lot of ground disturbance, I'm not a fan).

Another typical use is to use a bored pier at depth (say 4m), then fill the bottom 2m with concrete and backfill the rest with the disturbed soil. Again an anchor rod is dug in and protrude up to the ground line.


Most examples (bowles etc.) are based on horizontally loaded Deadman anchors only. A few others say to split the problem into, 2 independent checks. An horizontal earth pressure assessment, and a vertical pile assessment for uplift.


This seems to work fairly well, accept for uplift cases in drained condition's. The capacities are very low, in theory, by this hand method. They have been used succefully in the past, at scale [neutral]


Is there any texts or literature that address this problem?
 
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What problem? Guy loads are purely tension, the bulk of which is uplift. Its the nature of the beast to have to deal with uplift criticalcality.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."
 
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If you aren't getting a lot of geotechnical capacity against uplift, sounds like you need a heavier or deeper deadman.
 
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The horizontal component is resisted by soil passive pressure.
The vertical component is resisted by the self weight of the anchor and soil above.

What's your question?
 
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For the vertical component, what weight of soil do you consider? The buoyant weight assuming it is submerged? and/or the immediate projection of the plan area? Do you increase this assuming an angle of 20? degrees (or whatever) from the vertical?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
 
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For the vertical component, what weight of soil do you consider? The buoyant weight assuming it is submerged? and/or the immediate projection of the plan area? Do you increase this assuming an angle of 20? degrees (or whatever) from the vertical?

Buoyant weight. Typically used in flat open terrain, so not that unlikely there will be a high water table.

Just assuming direct plan area. For the bored pier version, the standard says it is ok to use skin friction in uplift. This works fine in undrained conditions, only problem is, it will drain at some point. Then according to pile theory, the capacity drops substantially.

These have been in use for decades with no issues. The hand calcs seem to underestimate the capacity. It would be interesting to see what a plaxis model says.


When i say they've been in use for decades, i'm trying to review a standard design that's been in use for decades....... there would be 100's, if not 1000's installed......
 
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