If you use a back hoe, use precast concrete sewer pipe as permanent
formwork. As a bonus, you will have the extra mass and reinforcing of the
Go to your local precast concrete plant and pick up damaged (on the
flanges) precast pipe sections. Be sure to get a section larger than the
engineered base the tower manufacturer recommends. Dig your hole with a
backhoe, fill the bottom with gravel and install the precast pipe in the
hole. Plumb the pipe and install the required reinforcing steel inside the
"form". Back fill the excavation with compacted fill, and pour your
concrete. We have done this several times and the local pipe precaster is
always eager to get rid of sections of pipe with the flanges damaged.
Backfill actually can be better than the original undisturbed earth. I
have been on several projects where the soil was not suitable, due to
organic materials, and had to be removed, and new compacted fill installed.
Check with a local Civil engineer for proper procedure with your local soil
type, but typically a "road grade" fill, installed in 3-4" lifts and tamped
down will perform very well. If you are really concerned about your back
fill, they can do a field test for compaction, using the modified Proctor
test. Soils can be engineered just like the rest of the tower installation.
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Administrative requests: towertalk-REQUEST@contesting.com