Posted on 08/18/2007 12:28:58 AM PDT by yorkie
A national mine safety expert believes the two collapses at the Crandall Canyon Mine [snip] were caused by "bumps" that resulted from the way operations were being conducted at the Huntington mine. Mining bumps are pressure-shifting seismic events than can cause the walls, pillars, ceiling and even the floor of a mine to literally explode and disintegrate. They can cause deaths and injuries, and can result in cave-ins. [snip] And while an investigation ultimately will determine the cause, Ferriter told the Deseret Morning News on Friday he feels certain the bumps were caused by mining activity.
"In my opinion, based on the evidence and the way it's described, I think it definitely was a mining-induced bump," he said of the initial Aug. 6 collapse.
[snip]"Earthquakes happen naturally. Bumps are a coal-mining phenomenon," Ferriter said, adding that bumps are more severe in Utah mining because thick (as much as 300 feet), heavy beds of sandstone often exist above mining operations, placing a great deal of stress on the man-made caves beneath them.
[snip]Ferriter said it is his understanding that around the time of the Aug. 6 collapse, miners had been extracting coal from the pillars themselves.
"Often, it's when you try and take too much of the pillar" that bumps occur, he said. "I understand they were retreating out of that section and taking some of that pillar out on the way out, maybe shaving it or splitting the pillar to get the coal. The more you take, the greater the load on the rest of the pillar."
And that is what may have led to the Aug. 6 bump, which registered 3.9 on the Richter scale.
"That's my opinion. (Miners were) taking too much" of the pillar, Ferriter said.
(Excerpt) Read more at deseretnews.com ...
The United Mines Workers are mostly a rare thing in the western US.
Just this morning, another earthquake in the area.
AlGore and environwacko pals will paint this as coal mining at its evil worst.
“The United Mines Workers are mostly a rare thing in the western US.”
That’s right, and that’s why I suspect their comments of being “agenda driven!”
So, the only thing an intelligent person does in college is science or engineering. Right.
They could have been following the plan. Things don’t always go according to plan!
Strip mining of coal is probably safest, although accidents can happen with large machinery. But, strip mining of coal is high on the list of environmental disasters around Pittsburgh as the Mon River was determined to be dead from open pit runoff. However, strip mining can be done safely WRT the environment and surface reclamation although it is more expensive. Coal is already twice the cost it was a few decades ago and these fatal accidents are sure to drive the cost higher. There is coal to last centuries and Peak Coal is still decades off, worst case.
But the bible didn’t mention any such things as scientists or science, so how do we know it’s true (/sarcasm).
Definition of an “expert:” Someone who lives 50 miles farther away and charges 3 times as much.
I am confused by the conflicting stories. On another thread a poster said there was seismic activity in the area of the mine in the days before the event where miners were trapped. There seems to have been seismic activity after the event that trapped the miners- and now you are saying another earthquake in the area has occurred. I have NO knowledge of this type of thing but to me that points to what the mine owner is claiming. I don’t understand the explanation that the mining incident itself was the seismic event. How does that explain the other seismic activity before and after in the same area?
Another thing I question is when I read about earthquakes or watch a show about them- what keeps coming up is how little even the experts know about the true causes and effects of quakes and aftershocks- there seems to be no real pattern that can lead to further understanding, or predictability of these events. Each event can be very different even in the same area, which is why so little is known. It is hard to study something that is ever changing. With this in mind- how can they know for sure if the mining caused the events or if what is happening is a natural occurance?
education is not a cure for stupidity.
--Kant, Critique of Pure Reason, 1787
If were up to Al Gore he would have Mr. Pigbearman seal up the mine to keep the Reptilian hive contained. /sarcasm off
Reclaimed land can be far superior to the natural land. In Fairbanks where water giants were used to clear 100 feet of frozen muck and then the floating dredges used to scoop gravel, the gravel left behind provides the most stable building surfaces around here. While modern mining requires settling ponds and dams and looks sweet only to engineers, when it is all over the land is much improved and has actual positive value.
What I heard was the motion associated with the seismic event was vertical, which is not typical for an earthquake, but would be consistent with a mine collapse.
I have been in the mining business over 34 years. After a disaster, you usually see the same group of “experts” and politicians on TV criticizing the operator, criticizing MSHA and calling for more regulations, without regard to the real facts of the particular situation. I listen to their positions, but filter their conclusions through the prism of my own experience. Rarely do I agree with the usual cadre of instant “experts” and always wait for the facts to come out, but in this case I find myself in general agreement with some of the critics regarding the mining plan.
The map of the Crandall Mine is posted on the MSHA site. The mine was developed out to the boundary with main headings using the room and pillar technique. The pillars are blocks of coal that are left to support the roof and overburden. The rooms are formed when the coal is extracted. The rooms in these main headings were the main travelways, haulageways, and ventilation ways.
Having reached the mining boundary, the Crandall Mine was pulling back, using a technique called “retreat mining”, or in the WV coal fields “pillaring”. During retreat mining, the roof support pillars are mined. The pillars can be removed because the main headings no longer need to be maintained. There is no need to get through them after all of the coal is mined. Another term for this technique is “robbing” pillars.
This is a technique that is commonly used in the coal industry. As enough of the roof support pillar is mined, the roof collapses “inby” where the miners are actually working. You want the roof to collapse to relieve the stresses on the pillars that remain where you are actually working, and in the travelways between you and the outside of the mine. The pillars support the roof, or the overburden. The deeper below ground (vertically)the mine is, the greater the load (stresses) on the support pillars. If the roof does not cave (fall) after the support pillars are removed, the load these pillars were supporting is transferred onto the remaining pillars, increasing the load on them.
In the eastern coal fields, where the cover is relatively shallow over the mine, the roof caving after pillar extraction generally is effective in controlling the load and stress on the remaining pillars, so it is generally safe to mine using this technique. The type of rock strata above the mine is also a factor.
Out in Utah, the mines are much deeper, so the load is much greater on pillars. If there is a thick band of hard sandstone in the rock strata somewhere above the mine level, this tends to not fail when the rock below it might collapse after pillar extraction. Therefore, the load shedding on remaining pillars that usually accompanies roof caving during retreat mining is not as effective. You have two factors working against you during retreat mining in a situation like Crandall. First, you have high stresses in the support pillars due to the depth. Second, you have stresses building up in the remaining support pillars as pillars “inby” are removed. The bumps referenced at Crandall are caused by the mountain trying to find equilibrium. At some point when the stresses become high enough, something has to give. In some mines the floor cracks and heaves up. I have seen a room that was 5’ high on Friday be 3 or 4’ high on Monday. In some cases the stresses build up in the pillars. There is a lot of stored energy. Rock under pressure can explode, and it does’t take much to relieve the pressure. The shock wave from a mountain bump could do it if the stresses are high enough in the pillars. An earthquake could do it. A shock from blasting can do it. We call this sudden pressure release an outburst or rock burst. This appears to be what has happened at Crandall, on a scale that I have never seen. The mine roof did’t collapse, the walls and perhaps the floor have exploded inward and filled the mine main headings. This is what the rescue team was mining through when the second accident occurred.
To add complexity with the above scenario, very large areas on each side of the main travelways where retreat mining was being conducted were mined out using the longwall technique. Longwall mining differs from room and pillar mining in that all of the coal is extracted in a longwall panel. The roof is designed to cave behind the longwall unit as the coal is extracted. No support pillars are left in place. To the extent that roof caving behind the longwall unit did not fully relieve the stresses in the roof immediately above, the remaining stresses would have been transferred out to the support pillars in the main headings, increasing the load on them.
This third factor, longwalled areas immediately adjacent on both sides of the rooms where support pillars were being extracted, likely made a significant contribution to this disaster. It appears support was removed systematically transferring additional load to the remaining pillars, where they failed catastrophically due to the pressure.
Is there anything illegal about this practice? No. In fact, MSHA had to approve the written mining plan, and did so about a month or so before the disaster. However, to me and to others I have talked to in the mining industry, this entire setup seemed risky.
In the end it may turn out to be an earthquake which triggered the rockburst, but I think it is just as likely, perhaps more likely, the mountain shifting to equalize stresses created the shock wave that released the stored energy in the pillars.
Trust me, they WERE pulling pillars and taking some of the barriers between the gob and the mains.
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