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Author Topic: Tower installation in rocky ground?  (Read 4476 times)
VE3VID
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Posts: 145




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« on: February 10, 2011, 07:13:37 AM »

Hi and thanks for reading..........

In the spring I will be moving my station to a new location.  Its high ground and very rural, but the ground near where I'd like the installation may be very rocky - Canadian Shield.  I currently have 2 towers: Delhi 68 and Delhi 56.  If I can not dig the usual hole for the base forming because of boulders, or more likely 1 huge house sized boulder, what other options are there for installation?  Drill into the rock?  If you know anything about this, or have dealt with this challenge in the past I like to hear from you.

Cheers
David
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WG8Z
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Posts: 216




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« Reply #1 on: February 10, 2011, 07:32:25 AM »

http://lists.contesting.com/_towertalk/2010-02/msg00371.html

http://www.wd0m.com/tower.html

Just Google "tower installation in rock"
many sites of info available.....
NRG has some good documentation

Have fun and be safe
Greg
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VE3VID
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Posts: 145




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« Reply #2 on: February 10, 2011, 06:56:47 PM »

 Huh
So the Google info says bind some re-bar to the rock, then pour a slab on top of the rock to sink the tower legs into.  Delhi DMX towers have 3 legs that would normally be sunk into the concrete base.  It would seem simpler to drill holes into the rock and bind them directly to the rock.  As said, the rock is at least as big as a house, more maybe?
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NA0AA
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« Reply #3 on: February 11, 2011, 03:46:10 PM »

You are going to have to locate and dig, and then engineer depending on what you uncover.  A real engineer will be needed.

It will depend on the nature of the rock, the size of what you have to anchor to.

Drilling and pinning is probably not much easier or cheaper than blasting and pouring concrete, but only an expert will know for sure.  Since you might also blast for a septic system, it might be even more cost effective.

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W8JX
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« Reply #4 on: February 12, 2011, 03:24:50 PM »

I would go with drilling and blasting. Done properly it should not be too expensive and it could yield a nice big hole full of fractured rock in a day or two at most.  It is either this or have a large heavy plate made to have tower base welded to and plate anchored to rock with proper lag bolts. 
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You can embrace new computer/tablet technology and change with it or cling to old fall far behind....
KC8WUC
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Posts: 54




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« Reply #5 on: February 13, 2011, 09:09:25 AM »

Drill and blast or drill or blast, that is the question.  As a previous poster said, whether you drill and pour hydraulic cement (it expands and fills the holes and voids, rather than contracts) and set the legs in the holes will depend on the type of boulder you're dealing with.  If you are dealing with sandstone, shale, or other crumbly rock (even degraded granite or limestone wioth laminations), you'd be better off excavating where possible or blasting. If you drill, an SDS drill with a large diameter drill bit or rotary hammer may do the job, or if you're working in close quarters, rent a rotary type jack hammer and put a drill bit on it.

If you blast, you'd best leave this to a qualified blaster who is used to doing close in utility and construction work (e.g., blasting close to structures, setting utility pole holes, blasting close to pipelines), perhaps your local utility company.  Even if the blast is not within close proximity to an inhabited structure, rarefraction waves from blasting can travel a considerable distance and cause damage if not attenuated or dampened.  Shooting holes is best done with individual charges using short delays between charges, charging holes lightly (not loading the hole completely with powder).  Use of blasting mats around the hole or even over the hole may be necessary (although certainly less spectacular than a lift shot that throws rocks and dirt every where).  Use of stemming, such as pea gravel to half the depth of the hole that you've dug is necessary to control the blast, otherwise you'll lose the power of your explosives to air blast.  For more info, consult the ISEE Blaster's Handbook for guidance (word to the wise: the ISEE handbook uses older powder loading factors/formulae that is a bit generous and uses more than enough powder and may cause overbreak).

73,
Michael KC8WUC/WDE0344


former blaster (Austin Powder Company, Dyno Nobel, Hilltop Energy, Inc.)
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K2GT
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Posts: 5




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« Reply #6 on: February 13, 2011, 10:21:51 AM »

I had my contractor install the tower when he built my house. He drilled into the rock (3 feet down) and rebarred it, and built a concrete pad above it and installed the  tower ground plate bolts into the concrete, and then mounted the tower on that. It's been up 6 years and has an HF Quad and a half dozen vhf/uhf antennas on it, cranks up to 55 feet, and has lived regularly through 90KM winds (while my wife screams get out there and crank your tower down!). It seems to me he pretty much did what your Google link said.
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VE3VID
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« Reply #7 on: February 13, 2011, 02:25:03 PM »

Luckily I know 2 engineers.  The rock is good old fashioned granite.  The surface soil is in most places only a couple inches deep.  In many places the rock peeks out making hills of stone.
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KC8WUC
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Posts: 54




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« Reply #8 on: February 13, 2011, 03:29:28 PM »

In that case, I'd either get a rotary drill, jack drill, or jack hammer, load it with powder (i.e., dynamite, water gels, cartidged ANFO, etc.) and blast if you can't mechanically bond the tower legs to the rock.

73,

Mchael KC8WUC/WDE9344
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KI4JEK
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Posts: 3




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« Reply #9 on: February 21, 2011, 04:38:32 PM »

You might think of mine roof bolting in reverse.  Get a sinking hammer 4 and 8 ft. drill steel, 8 ft. rock bolts and some epoxie resin.
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