[TowerTalk] Solutions for Tower Base in Fresh Water?

[John Lemay]

Larry

 

Sounds like you need some professional help here !

 

To answer some of your questions ...

 

Yes, concrete will set if it is placed in water. There would only be a
problem if it was running water such as a river, which would leach out the
fines - you don't have that issue.

 

Steel reinforcement (rebar) is often corroded by the time concrete is placed
around it, and the corrosion is then halted due to chemicals in the
concrete. This is only partly helpful to you because you also need to
consider the inside of the tubes.

 

If you try to dig a hole much below the water table in sand, the sides will
collapse. If you happen to be daft enough to be in the hole at the time, it
can be lethal.

 

Broadly speaking, you should aim for the same volume (and weight) of
concrete as the manufacturer calls for, but make it wider and less deep.

 

John G4ZTR

 

  _____  

From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Larry Libsch
Sent: 19 March 2012 12:37
To: towertalk at contesting.com
Subject: [TowerTalk] Solutions for Tower Base in Fresh Water?

 

Group -

         Our club has bought a tower for use at our new club shack on
the edge of the 'glades. The 'glades is fresh water this far north and
west. The water table at the site is 30 inches below ground level. The
soil is mixed gravel, sand, and earth fill for about 2 1/2 feet, then
wet sand below 30 inches.  Our tower is an old Rohn  with a three legged
tilt base to which the tower attaches. The Rohn plans for a concrete
tower base suggest the bottom of the 6 foot, open, galvanized steel legs
of the tilt base be placed into 9 in of (dry) sand and the concrete base
poured around the legs above the sand. It seems likely that the the tilt
base legs below the concrete base will always be in water, and that
water will stand inside the legs to the level of the water table. Much
of the concrete base will stand in wet sand below the water table.  As
concrete is water permeable and drys slowly, it is likely that the
outside of the tower base legs will also be wet from the top of the
concrete base down.  We seek an understanding of the special problems
this situation presents to the safe construction of a tower base and
solutions to those problems. So far, we recognize three likely problems:

         1)   Corrosion issues with the steel legs both inside and below
the concrete base. What can we do to minimize this problem?

         2)   It seems likely wet sand is a less firm base than dry
soil. What changes should we make to the size and /or the shape of the
concrete base from the Rohn plans?

         3)   Any hole deeper than 30 inches fills quickly with water.
Will we be able to dig a hole 7 feet deep and 5 feet by 5 feet wide? If
we manage to dig an acceptable hole, it will fill with water.
          Can we pour concrete into a water filled hole and have it set
up properly?

                                                                        
                                                                        
     Larry,  K4KGG

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