[TowerTalk] Guy Wire Anchors

[jimlux]

On 4/14/20 11:53 AM, Richard (Rick) Karlquist wrote:
> The discussion of "Class 1", etc soils reminds me
> of trying measure ground conductivity values for
> NEC simulation.  Real grounds are just way too
> complicated and inconsistent vs location and
> dependent on seasonal moisture for it to be possible
> to do a realistic "engineering analysis" for
> something like a screw in anchor.  I have
> a few feet of pure clay above cemented hard pan.
> I can't imagine getting the screw to go into
> my hard pan just with an impact wrench.  The
> depth to the hard pan varies depending on where
> you are on the property.  The clay above the
> hard pan will not hold anything when it
> is saturated with water.  But wait, I had
> the property "ripped" to a 7 feet depth with a D10
> Cat.  Now, depending on the luck of the draw,
> you could hit one of the fissures in the hard
> pan and get no grip.  The fissures also open
> and close seasonally.
> 
> I can't depend on testing because the clay
> when dry is like concrete and would give a
> high holding power at the time of test.
> 
> As was was pointed out, the mere weight of
> concrete + dirt makes the soil composition
> much less important.
> 

This is where hiring an engineer who knows the local conditions is 
important.

The auger anchor is a "engineered" solution that, in some cases, might 
be better than digging and concrete, but it is notably dependent on soil 
properties. There are "poor soil" designs for augers that basically 
assume you're on sand with nothing else, but that's going to either be 
small loads or giant auger.

There are also applications where the "instant" aspect of driving an 
auger is important.  You plant the anchors, erect the tower, and you're 
done in a day. No waiting for the concrete to reach desired strength, no 
excavation permits (augering usually doesn't count as "displacing 
soil"), which around here are needed for excavations more than a few 
cubic yards.



The engineering required for "block o' concrete" is less, and can be 
done so that you don't care about the soil properties (assuming the 
concrete doesn't sink out of sight in your squishy salt water marsh that 
you chose for its outstanding RF properties).

This is a lot like discussions we've had on the list about bases for 
freestanding (unguyed) towers, where rather than "giant cube", people 
have designed crosses or flat plates which have some advantage over 
"giant cube"