.
I my experience in installing concrete bases. of varying sizes and challenging
soil composition.
The more challenging being Shale, Sandy loam and wet land ( where you had to
pump the water out as you filled the void with concrete.
I preference was always to fill the base with concrete to undisturbed wall ( a
challenge in shale and loam ) and build a 2X8 or 2X10 top form held in place
with cross 2X4 and concrete steel nail stake spikes. ( read three at each end =
32 spikes) In the larges I ever did an 5'6 X 9' for an HDX89 in a shale
ground. The finial pour was @ 13 yards . Not an engineer by any means but
felt the side wall adhesion was IMO critical in free standing towers.
As for N6BV HFTA ... K6TU has a great site to see or plan what going on in
your yard http://k6tu.net/?q=TerrainProfiles
Wayne W3EA
________________________________
From: TowerTalk <towertalk-bounces@contesting.com> on behalf of Paul
Christensen <w9ac@arrl.net>
Sent: Friday, February 3, 2017 9:03 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Tower Foundation Pouring
Yesterday, I just poured nearly 40 sq. yards of concrete (4 concrete trucks)
in preparation for moving two self-supporting Pirod towers. One tower is
140ft., the other is 100 ft.
When the contractor dug the ground for the base piers, it only took a couple
light rains to cause some side wall cave ins. The soil is composed of
sand/dirt and it's just impossible to dig a square hole and have it stay
that way. In retrospect, we should have placed tarps against the side walls
to allow water to drain into the pit while keeping the wall area dry.
Ideally, the pour would occur shortly after the dig, but county inspections
and re-inspections slowed us down.
Plywood and 2x4 lumber was used to frame the base pier. Despite efforts to
brace the walls from blowing out as concreate was added, we still had slight
bowing on the 140 ft. tower base (a 10 ft. x 10 ft. square). That resulted
in a less than perfect square on two sides of the top surface. It's a
cosmetic thing that drives someone like me crazy -- just as when I see a
picture tilted on a wall.
In thinking through the problem while I drove an hour home last night, what
we *should* have done was to create a separate and isolated 2x4 or 2x6 frame
on top of the boxed pier base. That way, the walls could blow out slightly,
while leaving the top 4"-6" perfectly square. Some concreate would escape
and leak out under the top frame, but that can be managed by compressing
dirt around the perimeter. We could have easily done that since we had two
tractors with push plates to fill dirt as concrete was poured. Again,
hindsight is 20-20. Still, the story ended fine and it's all structurally
sound. The pier for the 100 ft. tower ended up perfectly square as it's a
bit smaller with less opportunity to blow out with bracing.
Anyway, something to consider if any of you will one day need a very large
base pier.
Paul, W9AC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
TowerTalk Info Page -
Contesting<http://lists.contesting.com/mailman/listinfo/towertalk>
lists.contesting.com
TowerTalk is for discussion of tower and HF antenna construction topics. TT
members have lots of helpful information and are happy to share it.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|