[TowerTalk] Bedrock

[Charles Lind]

A while back I posted a question about digging a tower base when bedrock
was (probably) just a few feet down.   The tower was a U.S. Tower TX 455,
and required a 6.5 foot deep hole.  It was likely that much of the 100
acres we  had available was on the Niagara escarpment, with limestone at a
depth of about 3-4 feet.  We got out a large excavator, and indeed hit rock
at 3.5 feet.  Then got out a bigger excavator and tried to smash the rock.
Not only was it impossible to even dent it, but the surface was as smooth
as a highway.  Not to be deterred,  we took a rotary impact hammer with a
two foot bit and drilled 4 holes at 45 degree angles aiming toward the
center of the pit, and 4 vertical holes, then drove in 7/8 inch
rebar--potted in with hydraulic cement.  Over that the prescribed rebar
cage was placed, although that had to be shortened with the help of an
oxy-acetylene torch.  Three yards of 3500 psi concrete was placed on all of
that, and allowed to cure for a month.  The tower was installed without
incident, and has since survived 60 + mph winds.  Thanks to all who offered
advice.......

Chuck, N8CL