AM tower ground prep over water

[Transmitter Man]

I'm looking for any information as to what's involved in the preperation of groundworks necessary to install a relatively short mast or tower over a flooded area of ground?

Just how do you dig a hole, fill with concrete and keep the water out?

Steel shell?

Phil

 

[greenie]

Most contractors can handle that. On the other hand, you will have a very hard time getting a building permit to do it. Here in Florida for example, "wetlands" is off limits. period!

 

[Transmitter Man]

This potential job is here in the UK where we also suffer strict regulations for such structures.

However, it's for a college station and they own a large tract of land and planning permission should be relatively strait forward.

What I'd like to try and find out is a little about exactly how a contractor would go about tackling this job?

Thanks.

Phil

 

[amfmsw]

Saltwater or Fresh water? BIG difference. WFPG-AM Atlantic City was grounded directly into the sand under Steel Pier. Copper rod driven deep. Nothing else needed. Nature did the rest. Fabulous signal. Now a folded monopole in marsh.

 

[Transmitter Man]

Hi,

I wish it were salt water

It's a freshwater pond, but that's better than rock or sand without the sea water.

I'd still like to find out how one sinks a concrete base into it.

Phil

 

[rrsounds]

Hi,

I wish it were salt water

It's a freshwater pond, but that's better than rock or sand without the sea water.

I'd still like to find out how one sinks a concrete base into it.

Phil

They might build a form from lumber or metal and seal it water-tight, out of the water. Depending upon whether the ground is hard or soft, it might be open-bottomed (hard earth), or have a hole just large enough to dig through to remove earth as the box is lowered into place. Either way, they'll be removing earth as they lower the form.

Once they have the form in place and they have removed all the earth and most or all of the water, they can position whatever metal reinforcement they require along with the tower base inside the form, and then pour concrete. They may need to pour in stages, letting it harden along the way. FWIW, they may not be able to remove all of the form once the entire concrete base hardens, but that's not really a problem.

The other possibility is to use special concrete slurry that can be poured directly under water. But they'll need to construct a form, no matter what.

While it may not come cheap (does anything anymore?) there's plenty of experience in this field, and this kind of thing is done fairly often. Look at all the bridges with concrete piers...

Kind Regards,
David

 

[Transmitter Man]

Hi David,

OK, that's filled in my lack of knowledge on this subject.

You may remember we met on the BW stand at IBC a couple of years ago.

I'm one of their dealers here in London.

Now I know you once engineered at Z100 and designed the Ariane. How did you find time gain knowledge of digging holes in water ;D

Phil

 

[rrsounds]

Hi David,

OK, that's filled in my lack of knowledge on this subject.

You may remember we met on the BW stand at IBC a couple of years ago.

I'm one of their dealers here in London.

Now I know you once engineered at Z100 and designed the Ariane. How did you find time gain knowledge of digging holes in water ;D

Phil

Phil,
When I was a kid, I wanted to be a civil engineer and build bridges, highways and railroads. That was until I found out how much math that required!

I'm still fascinated by such things, and, ironically, I had to learn the math anyway to understand electronics. :-\
Nice to hear from you...maybe we'll meet again.

Kind Regards,
David

 

[Transmitter Man]

Yes, look forward to it.

If I get the go ahead and build this local AM and you visit the UK you'll be employed, at great cost to come and setup the processing

I have budgeted for a DSPX with Ariane.

Should sound nice driving a 500w BE on AM.

Phil

 

[LA_Guy]

Cofferdams

They generally use cofferdams, which are these splined pieces of steel that interlock in a tongue and groove system. To keep them sealed they use-cow $*it!

The pieces are driven into the bottom with a pile driver, then the water is pumped out.

Here's an example: http://www.tpub.com/content/construction/14044/css/14044_300.htm

http://www.javeler.com/images/TightSpaces5.JPG

 

[rrsounds]

Re: Cofferdams

They generally use cofferdams, which are these splined pieces of steel that interlock in a tongue and groove system. To keep them sealed they use-cow $*it!

The pieces are driven into the bottom with a pile driver, then the water is pumped out.

Here's an example: http://www.tpub.com/content/construction/14044/css/14044_300.htm

http://www.javeler.com/images/TightSpaces5.JPG

Cool site. LA_Guy! I LOVE stuff like that! I know we're going way off topic, but, speaking of cofferdams ... When they were constructing the Hoover Dam, they drilled and blasted huge tunnels ("penstocks") into both sides of the canyon that allowed the river to be bypassed, and then they built massive earthen cofferdams upstream and downstream of the dam site, and drained the area. This allowed the crews the freedom to remove earth down to bedrock, for a secure footing for the concrete.

One thing I found really fascinating (actually, the whole project was incredible) was that because concrete generates heat as it cures, they built a refrigeration plant and an intricate network of cold water pipes pipes into the construction to artificially cool the concrete. IIRC, otherwise, it would have taken over a hundred years to completely cure...

BTW, completion of Hoover Dam came in early and under budget. I've read a couple of books about the project, and the story reads like a novel.

Back to the subject at hand... Phil, please keep us informed as your own project progresses. And take lots of photos!

Kind Regards,
David

 

[EncSpy]

from what I read the concrete in hoover dam is still curing!!!

 

[Transmitter Man]

Hi guys,

Many thanks for taking the time to explain and supply the links.

Now I know what a cofferdam is having seen them at various construction sites over the years.

If I get the go ahead for this LPAM build then I'll certainly take plenty of pictures for the scrap book.

The remit is to build a 1w EMPR (5-100w of TX power is typical for these stations based of course on antenna system efficiency) station where the license reg's stipulate a max antenna height of 20m (around 66').

This is to be college station here in the UK. The college has a large tract of land but does not really want to have to fence off an area so large as to encompass a buried full-size grond system or even go to an 4-6 wire elevated ground.

What they do have is a medium size pond which sits over a ground fed stream with a clay base (there's lead in that there clay).

This pond is never dry and is around 3-6 feet deepand surrounded by trees.

I wish I had some modelling software to play with as initial thoughts were to fix an almighty large horizontal capacity hat atop a 66 foot tower and then take some measurements.

My MF antenna knowledge is not great though I can call on a couple of guys that worked out on the pirate ships in the 60's so measurements and tuning will not be a problem.

I am looking for best bandwidth and efficiency without having to use too much inductive loading to reonate the antenna.

The authority's issue licenses for the high end of the band from 1134KHz and higher.

I wanted to stay away from a guyed mast if at all possible and at 66' high this should enable me to use a fairly narrow face width sectional tower.

Your thoughts as this is totally new territory for me.

Phil

 

[CW]

from what I read the concrete in hoover dam is still curing!!!

Correct...it will cure in less than the 150years it naturally would take but it IS still curing....when I took the HardHat tour in 99, the tour guide told us the facts about the concrete, etc...there is a lot of "internal" leaks...places where water still trickles through the center of the dam....amazing!!