[TowerTalk] Fwd: Relatively large tower base install questions.

[Patrick Greenlee]

Roger, Brian, and Steve, Thanks for your input.  Irrespective of a PE, his 
E&O insurance, or other considerations I would NEVER erect a tower like this 
within a tower's height of a building or generally occupied area. I will 
risk my black Angus herd and put the tower into a pasture.

When I built my current house I hired a professional consulting soils 
engineer recommended to me by the civil engineering firm I used.   He is the 
one they used for projects above their level of expertise.  He subcontracted 
for a drilling rig to bore a 6 inch diameter hole stopping every 6 inches on 
the way down to take samples until they hit solid rock. The tests indicated 
a very slight negligible expansive soil content. Subsequent excavation of 
intercepting trenches for ground water amelioration as regards a basement, 
trenching for water lines, trenching and drilling for multiple wells for a 
geothermal field and other trenching for drain lines, septic tank, leech 
field, and so forth indicate the character of the soil in the surrounding 
area to be essentially indistinguishable from that of the test bore.  I have 
the report, complete with his PE stamp attesting to the support 
characteristics of the soil and his design recommendations for a foundation 
and various ground water amelioration strategies to keep the basement dry.

I am satisfied his report will adequately support decision making re the 
tower in question. I will solicit some engineering assistance to quantify 
the depths and diameters of the 3 piers as that is not within my expertise. 
I have my opinion but will have it "sanity checked" before mixing concrete. 
I suspect that since the loading in all respects is significantly less than 
when at its full 100 ft with wind generator on top that if I come close to 
duplicating the original piers I will have significantly more holding 
proportionately than the original installation which is far more than needed 
now.
Our code frost depth is 18 inches so frost heave is not a consideration as 
the piers will be way deeper.  As far as belling the pier hole at the bottom 
is concerned... well it can't hurt but in practice it doesn't do as much for 
you as is often predicted.  Real world experience often indicates it doesn't 
do much and that irregularities in the walls of the pier hole are the chief 
contributors to pullout.  It certainly won't hurt and I have the capability 
to shape the pier hole like an inverted cone with the big end at the bottom 
which does increase pullout force.

I examined the tower in situ and saw no evidence whatsoever that the piers 
were ever disturbed.  They are still dead on as per spirit level and laser.

Suggestions regarding the disassembly are solicited.  Someone may think of a 
better order of removal of pieces or other considerations than I have.  My 
initial thought is to place a temporary three point guy of ropes on the two 
hinged legs and lower them by the guys letting them pivot down to the ground 
after removing all the cross braces from them. The last leg (non pivoting) 
would have a 2 3/8 inch welded steel tube lashed to it with the steel tube 
in contact with the ground.  Then the bolts connecting this last leg to its 
pier would be removed and the leg lowered down by means of its rope guys. 
The lashed-on tube will keep the leg from falling down the height of the 
flange above ground.  This little touch may not be deemed a requirement. 
I'll wait to see how the first two legs react before deciding if it is 
needed or not.

Please feel free to offer suggestions or point out flaws. It is way better 
to find the problems in the planning stage than when large heavy things are 
being moved around.

Patrick AF5CK