[TowerTalk] Tower Foundation Pouring

[Paul Christensen]

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