Michael Goins wrote:
> It is not limestone. It is a rock shelf.
What kind of rock? Granite? Sedimentary? How does it stand up strength
wise/ for structures? Not all granite is good stuff and the larger
percentage of it is porous where water is concerned although there are
quarries that produce non porous granite. There is an epoxy that
expands as it cures so you can break solid rock without the need for
dynamite. I don't like dynamite because it tends to cause a lot of micro
fractures in the surrounding rock. It's a lot more fun to use, but noisy
and does have some side effects besides requiring a lot more safety
precautions. That and you need what is called a "powder license" to use
the stuff now days, but there are probably quite a few out in that part
of the country. With the epoxy you drill a series a holes in line, pour
in the freshly mixed epoxy, and then lift out the pieces a few hours
later, or the next day. There's a little more to it when digging a hole
and I don't know how much it costs. Someone on here did post a link to
the company within the last year or so.
Oh, you also want to bell out the hole to make it larger at the bottom
than at the top if it's going to get concrete.
Other than the occasional erratic around here, bed rock, which is
sedimentary is close to 400 feet down. OTOH some of those erratics are
BIG as in car or truck size with the rare one even larger. When I was
younger I used to find the occasional one while plowing which meant a
lot of work repairing the plow, digging out the erratic, and disposing
of the darn thing. The plows were spring loaded to trip when you hit a
big rock so it didn't do permanent damage. Over where I was raised,
nearly every farm would have a large rock pile some where. I had the
wind knocked out of me as I hit the tractor's steering wheel quite a few
times. The tractors and plows may be big, but those big rocks don't even
wiggle. <:-))
About the time we were building the new home South of Breckenridge MI,
the farmers who rented my dad's place hit a very large rock. As we had
the earth moving equipment digging the basement, we had them dig out the
rock and bury it out by the road. About 15 years later the power company
decided they were going to run a high pressure gas main along our road.
That was high pressure as in, not for residential use.
I watched them burying the main when I realized they were going to try
to go through out yard out by the road. I caught up with the foreman and
said they weren't going to be able to get through our yard. He just
turned contrary and basically said they could go any where they wanted.
So, I grinned, said OK, and got out the lawn chair so I could sit and
watch. They had just entered the yard when they hit that sucker which
busted up their "trencher" pretty bad. I'll swear that machine jumped
straight up about 2 or 3 feet. The foreman came up with a rather
dejected look and asked "how big is it" which I was trying to tell him
before he cut me off. I told him it was about the size of our car which
was back in the days of full size cars. They ended up going out into the
road to get by our place. I don't know what that rock weighed (I'd guess
well over 50 tons) but it took two big tractors so skid it from where we
dug it out to where we buried it.
73
Roger (K8RI)
> I have limestone here in
> places, but there are tremendous boulders and several huge rock
> shelves. It is in a rock shelf that is absolutely solid, not porous
> like limestone.
>
> Guys, I really appreciate the help.
>
> Michael Goins, k5wmg
> Professor, Writing
> University of Texas at San Antonio
>
>
>
>
>
>
>
> On Sat, Feb 13, 2010 at 6:02 PM, chas <chasm@texas.net> wrote:
>
>> Michael Goins wrote:
>>
>>> Guys, I'm needing some help here.
>>>
>>> I am installing a HG52SS about 16 miles north of San Antonio in an
>>> area that is nearly all solid rock and I have two sets of factory
>>> specs on installation instructions from HyGain. One says (and I'm
>>> going from memory here, but I'm pretty sure I am correct) 30X30X42"
>>> for the hole and the other says 42"X42"X5.5 feet for the hole. The
>>> issue is that under an inch or so of soil here it is virtually all
>>> solid rock. We are now down about 3 1/2 feet into solid rock on all
>>> four sides, and it has required a large jackhammer and many hours to
>>> get there. Assuming the base hole is to be designed for both
>>> compressive and lateral movement, there is no way it is going
>>> anywhere, either way
>>> Michael Goins, k5wmg
>>>
>>
>> Mike is trying to burrow into solid limestone which is prevalent all over the
>> Edward's Plateau until you get up to Lake Granite Shoals or about 40 miles
>> North of Austin when you get into granite.
>>
>> but from Fredericksburg to the NWest of SAT south to Hondo and back East to
>> black gumbo on the East side of I35, it is all limestone.
>>
>> and if he got two feet into it, my hat is off to him.
>> if it were my HG52 sitting on site, I would have flattend off about 4 sq ft
>> of base rock, drilled holes for the 1/2" base plate's all thread 1"+ diam
>> bolts about 4' long, set the base plate on its double nuts on the bolts in
>> their holes and about 4" proud of the rock surface then poured a slab with
>> rebar or heavy remesh. let it sit for a couple of days and then hoist the
>> base of the tower onto the base plate and bolt it down.
>>
>> I would call that a done deal for that area of Texas in that sort of ground.
>> Then, I would bring in about 12 cubic yds of iron ore from East of Austin
>> (look up Camp Swift) and spread that some 4" thick under top soil for a
>> ground and radial surface. sod over it and call it done. if you want, lay
>> some remesh in the iron ore as you spread it or some 20' sticks of 3/8 to
>> 1/2" rebar and hook them up for a ground field THEN spread your iron ore over
>> it, then topsoil and put some sod down on it.
>>
>> my opinion. I have black gumbo with 4 to 6" iron ore on top of it under some
>> 4" of topsoil and sod and it is superb for a radial and reflectant field
>> under my antennas, vertical or horizontal.
>>
>> fwiw
>>
>> 73
>>
>> chas
>>
>> --
>> chasm@texas.net k5dam Houston, TX
>>
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>>
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