On Sep 30, 12:03 am, Bob Officer <boboffic...@127.0.0.7> wrote:
On Tue, 4 Sep 2007 19:07:01 -0700, in sci.geo.earthquakes, "Robert
Flory" <wyo...@hotmail.com> wrote:
"Belba Grubb" <trungsister...@yahoo.com> wrote in message
news:1188955662.045081.117710@w3g2000hsg.googlegroups.com...
On Aug 22, 12:38 pm,
t...@sevak.isi.edu (Thomas A. Russ) wrote:
Well, other than what was in your article, I don't really know anything
about maountain bumps, but I would expect that the pressure is from the
tons of rock above the mine (overburden?) pressing down on the walls
and columns of the mine. Since the shafts and passageways are empty,
the pressure of the air is much lower than the rock pressure, and when
the rock structure fails, you would get a collapse.
I have yet to read any of those papers at the Google Scholar link, but
there seems to be more force behind it than would be expected in an
ordinary collapse. It is said in the general descriptions that a bump
blows coal out of a seam. The injured and dead rescuers were buried,
they say, under 5 feet of coal. And it happens quickly, too. Also,
there were reports of blast-like (my word for it; I don't remember the
actual words used in the news story) effects at the site of the
original tragedy that nobody could figure out a reason for at that
point. Bumps are apparently very rare, which would suggest unusual
conditions that cause them: ? methane or some other gas, although
heat doesn't seem to be mentioned anywhere so they probably aren't
true explosions. It probably is some effect of the rock weight and
air and/or other gas under pressure from that weight; since they
happen in mines, that too could be a contributor. If they always blow
coal out of the seams, then the gas might be coming from that. Very
interesting.
Of course, we're going to hear a lot about them at the congressional
hearings, but it's unclear, to paraphrase Ambrose Bierce, whether
those will shed more heat or light on the subject. Will have to look
at those articles some day when there is time.
Barb
----- Original Message -----
From: "Belba Grubb" <trungsister...@yahoo.com
Bumps are apparently very rare, which would suggest unusual
conditions that cause them: ? methane or some other gas, although
heat doesn't seem to be mentioned anywhere so they probably aren't
true explosions. It probably is some effect of the rock weight and
air and/or other gas under pressure from that weight; since they
happen in mines, that too could be a contributor. If they always blow
coal out of the seams, then the gas might be coming from that. Very
interesting.
I'm not a wiz at math and numbers, but 1800 feet of mountain dropping only a
couple of inches conjures up a truly frightening picture in my mind. I'm
sure if you were convert the energy released in a 4.7 event into the
equivalent energy of 1800 feet of rock falling onto a immobile surface, you
would find that the drop wouldn't have to be much. Any math wizards out
there? How far do you have to drop 1800 feet of mountain to get a 4.7?
I've not seen anything to suggest gas explosions or anything else played a
part in this tragedy. Someone misjudged or miscalculated the forces in
play. Then load exceeded the ability of the pillars to hold. Coal is
brittle and tends to shatter/explode rather that deform when it fails.
Actually the reports I have heard indicate that bumps were becoming fairly
common in the mine before the big bump. they certainly were common
afterwards. Mother nature apparently was giving fair warning. If you cut
the support down below a certain point, the whole mountain will start coming
down. When that starts, it won't stop till a stable configuration is
reached. Everything I have seen and heard is consistent with pillar
failure. The reports seem to suggest retreat mining ..or whatever else you
want to call it, was being done. Do that and at some point the roof will
drop. If you are lucky, it will be when you want it to, after you leave.
Sometimes it will be before you expect it.
Underground mining is and will continue to be dangerous. particularly
softer rock like sedimentary mines or rotten altered rock. IMHO - The only
STABLE mines I've ever been were true hard rock mines that didn't require
timbering. That said, even in hard rock mines, you pull out enough rock and
you end up with a sink hole or mountain collapse. I spent a childhood
running around in abandoned hard rock mines.... I spent the rest of my life
avoiding any mine that required bolts and such to hold up. A mine with
pillars of brittle coal never struck me as a health place to be.
Bob
I do know a little bit about mining and rocks. (: Der Coach has spent
his share of time there too, I suspect.
Take a hammer and swing it at solid rock, then examine the rock face
where you hit it. the rock structure has failed. In the type of
mining under discussion some of the coal is left in pillars to
support the overlaying rock. When the pressure from above (same as
the hammer falling) over comes the ability of the coal to support the
over burden's weight, the *most friable* material in the column will
fractures in failure.
Example find the most friable material
soil
siltstone
shale
Other stone
Coal pillars
Shale or other stone
granite
All it would take is a failure in one pillar to bring the entire
pillar system down in quick succession. All the force is pushed down
of the friable coal, and the coal (for the most part) has zero side
support. I bet not one person has ever thought about wrapping the
coal pillars in plastic packaging material this might *slow down* the
collapse of a pillar by giving it minimum side support.
You mean the the roof will fall instantly? As if a building blasted,
will fall down once the walls are blown away?
