I was in a similar situation when I built my station about 15 years ago.
It wasn't flat but had some areas where the anchors would have been in your
kind of soil. Solution: bring in about 15 or 20 yds of sand fill to make
a gently sloping mound where an anchor base was built. It lasted for 10
years before I moved and none of the anchors ever moved even though we had
several passes from hurricanes.
Assuming the tower is a Rohn 25 the hole really needs to be no deeper than
around 3 to 4 feet. This should be a solution for you.
Bill K4XS
In a message dated 3/19/2012 12:36:52 P.M. Greenwich Standard Time,
llibsch@bellsouth.net writes:
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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