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"
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|