[TowerTalk] new AN-Wireless tower, floundaion question
k3dua at erols.com
Fri Jun 30 16:44:13 EDT 2006
I guess the item I would look at is the total cost/effort. Yes, the
pad-pier uses less concrete and rebar, a cost savings. But is the
difference worth the time, and extra effort of 2 pours and renting the
tamper and backfilling. It is much simpler to use there 9 by 9 by 5
full foundation. One pour, no back fill, no tamper rental. Yes it
takes more rebar and concrete, but its a lot easier in my book.
On Jun 30, 2006, at 9:55 AM, ersmar at comcast.net wrote:
> It's nearly impossible to undercut safely the full size of the
> pad for this type of foundation. When I was working in the electric
> utility industry as an engineer, we used these foundations all the
> time for our substation structures. The crews dug out the full size
> hole for the pad (in your case, that would be a hole 9 feet by 9 feet
> by five feet deep.) They set the rebars for both the pad and pier,
> the poured the concrete for the pad. Next day they set the forms for
> the pier on top of the pad and poured the pier. ANd I believe there
> is a material that is applied to the concrete to allow this second
> pour to adhere to the first. Anyone help here?
> The next step is the trickiest: backfilling the excavation after
> removing the pier's form material. In your case you ought to back
> fill a foot deep around the pier, then spend a bit of time with a
> tamper banging the soil in compaction. You can rent a motorized
> tamper for this. Then add another foot and tamp it, etc until the
> entire excavation is filled and the earth put back in near-undisturbed
> My Trylon tower's foundation is similar in construction except
> that the undercut is a slanted cut only a foot wider than the main
> hole. I was able to use a spade, with proper shoring of course, to
> loosen the earth and haul it out with a backhoe. But yours is a bit
> too wide to safely support the overlying earth.
> I know - a PITA, but it has to be done that way so you don't
> injure anyone should the hole collapse.
> Good luck, and remember - On towers as in driving a car, there
> are no such things as accidents.
> 73 de
> Gene Smar AD3F
> -------------- Original message ----------------------
> From: "JC Smith" <jc-smith at comcast.net>
>> Hello All,
>> As mentioned previously I am stick-building (like a giant erector
>> set) a new
>> AN-Wireless HD-80. I will be posting photos at:
>> if anyone cares to watch it go up and the antenna stack go on it. We
>> started digging the foundation yesterday. It's a pad and pier
>> (like an inverted tee) with a 9'x9'x1.5' pad and a 5'x5'x3.5' pier.
>> Has anyone on here ever dug one of these by digging the 5'x5' hole
>> first and
>> then undercutting the bottom to create the pad? If so, I'd sure
>> hearing how you did the digging for the undercut. We got the 5'x5'
>> hole no
>> problem but our experiments (so far) with the undercutting haven't
>> been very
>> successful. We are in clay soil, fortunately with no rocks. If
>> don't go better today we will probably dig out the entire 9'x9' hole,
>> the pad, form the pier and backfill around it.
>> Suggestions appreciated.
>> 73 - JC, K0HPS
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