[TowerTalk] Looking for some foundation advice

[Grant Saviers]

A little googling and it appears that testing now verifies that long 
free falls aren't detrimental, but inspectors may not all agree, at 
least that is my somewhat aged experience.  Same for free fall pouring 
into 8 feet of water.

I'm surprised that free fall pouring into 30-50 feet deep water in a 
caisson is ok.  Pouring into some water at the bottom sounds more 
reasonable.

So better ask your inspection dept what is ok.

I was building over the Silicon Valley "plume".   Underground water flow 
with TriChlor etc contamination from electronics making in the 50' and 
60's.  The engineers said "we can't dig deeper than 2 feet" or we will 
trigger remediating $$$$.

Grant KZ1W

On 5/27/2020 16:49, Steve Maki wrote:
> On 05/27/20 19:34 PM, Steve Maki wrote:
>> On 05/27/20 19:15 PM, Grant Saviers wrote:
>>
>>> Actually it is ok to pour concrete into a wet hole if the concrete is 
>>> pumped in from the bottom. The water rises right out.  Not ok to drop 
>>> concrete into water.  The mix plant, pumper and driver know how to 
>>> adjust the mix a bit.
>>
>> Hmm - that's not my experience. When we (drillers hired by me) install 
>> caissons for tall monopoles and self supporters with 30'-50' deep 
>> caissons, they just dump the concrete in. They use temporary 
>> cylindrical forms to prevent cave-ins, but pay little attention to the 
>> water down there. These operations are always monitored by 3rd party 
>> engineering firms. On the reports I usually see *freefall concrete 
>> placement*.
>>
>>> Or have a PE design a different base, there are all sorts of 
>>> alternatives, plates, piers, wider and shallow, etc.  As long as the 
>>> base resists the overturning moment and shear. The stock foundation 
>>> UST wet stamp is on the web so should be a easy and quick job for a 
>>> PE (unless they want a soils test, which in theory...  but local 
>>> knowledge of conditions often is acceptable).
>>
>> Agreed. A suitable foundation can be designed for above ground 
>> placement if you don't mind the ugliness and the concrete cost. The 
>> key is to get it engineered properly.
> 
> In fact there are many 70'-100' cellular monopoles around Detroit on 
> ballast mounts. Often to avoid what is beneath the surface.
> 
> -Steve K8LX
> 
> 
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