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Post by ironhold on Dec 9, 2015 19:48:54 GMT
This one comes from the anime series "Kaze no Yojimbo", which I've referenced elsewhere.
Ten years before the story begins, someone pulled off a brazen heist. A cargo train was forced to stop on the tracks in the middle of a heavy rainstorm due to a rail crossing being blocked. When the train finally arrived at the station, they discovered that the rear car of the train had somehow become disconnected. None of the safety mechanisms that should have warned the crew were set off, and the rear car itself was never found.
Crime syndicate A was once the undisputed power-behind-the-power in a particular Japanese town near where this happened. Then syndicate B moved in at some point, setting off a feud. As part of it, syndicate B believed that A was responsible for the theft and that they somehow stashed the rail car inside a large mine that A owned near the city. B captures someone who is important to the leader of A, and so they're able to get the deed to the mine as a ransom (under the guise of a shady business transaction). They immediately send in two truckloads of workers to scour the mine, not aware of the true situation that's going on.
The mine in question dates back to the Meiji Era, indicating how old it is. After a century-plus of excavating, the miners finally hit a part of the mountain that was geologically unstable. To compensate for this, A decided to halt digging in that section. A chamber in the heart of the unstable area was reinforced with wooden walls and wooden support beams to keep it from collapsing. A wooden wall was then built over the entrance to the chamber, and a Shinto shrine dedicated to the memory of those miners who had been killed over the decades erected in front of said wall. The idea was that nobody would be crass enough to desecrate a shrine in order to get into the unstable area, adding an extra layer of protection.
Well, B decided to go ahead and do that, unaware of the mine's history; they were so excited about getting the mine that they didn't ask questions about its current condition, and so when they spotted a chamber that was on A's maps but not the survey maps they figured it had to be where the rail car was somehow hidden. In time, B's crew smashes enough of the walls and support beams looking for any possible hidden rooms that the chamber becomes unstable again and it caves in. The miners survive, albeit with severe injuries. When the police go to investigate, A points out the fact that there was a shrine in front of everything and that B would have had to destroy the shrine to get at the unstable chamber, meaning that it's entirely B's fault everything happened. (Everything goes down in episode #17)
1. How can one part of a mountain be unstable but not another?
2. What sort of engineering would be required to where simply shoring up a single chamber would keep everything from collapsing?
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Post by the light works on Dec 10, 2015 2:31:29 GMT
It is actually pretty common for a mountain to have an internal fracture that renders portions of it catastrophically unstable, but other parts of it are completely solid.
the key question of the shoring is if it was just that chamber that collapsed, or if it took out the entire mine.
the best example I can think of for engineered shoring is one of my local tunnels - the tunnel has alternating bands of concrete shoring and bare solid rock. as I recall, some years back, a crew was making repairs to the concrete and accidentally fractured a support band - leading to a collapse at that band. The rest of the tunnel remained intact.
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Post by silverdragon on Dec 10, 2015 11:05:05 GMT
This is common in old UK coal mines, they would hit a seam that made it unstable, and just retreat.
They would shore it up, sure, but just enough to make it "safe"...
You can mine elsewhere, but continuing to mine in the unstable bit could collapse the whole mine.
That has happened.
There have been disasters from mining "The wrong bit"
What kind of engineering?.. Pit Props.
Do a search on that.
Without proper supports, many mines would have collapsed by now.
This is also where modern house building gets things like Acrow Props from .. telescopic screw thread props that work like wind-up jacks.
They were used to temporarily shore up area's until the right length solid props could be found.
In some cases, when the seam has been finished, they will remove the props and allow a minor cave-in, after they had used the old hole as a trash dump for the stuff they couldnt be bothered shipping to the surface that was no good.
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Post by mrfatso on Dec 10, 2015 18:20:37 GMT
A classic example of a geological structure that would cause instability would be a paeloriver bed, which had cut across the ancient landsurface when the original organic material forming the coal was laid down.
These might contain loose, friable unconsolidated sands and gravel which easily collapse when tunnelled into them. They are also very difficult to predict a coal seam might cover a large area but the sand deposits occur only in certain specific areas.
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Post by wvengineer on Dec 11, 2015 1:39:36 GMT
#1 Mountains are usually not solid rock. Instead they are layers of different rocks stacked one on top of each other and the worn and weathered over time.. One prime example in the Eastern US is the Sidling Hill Cut for I-68 outside of Hancock, MD. upload.wikimedia.org/wikipedia/commons/3/35/Sideling_Hill_cut_MD1.jpgThe physical properties of the various layers of rock can vary greatly. If you were driving a tunnel though layers of rock like the above pic, you can imaging all the different type of you that you would have to deal with. This is actually a very common problem when people are boring tunnels or mines. They can transition from one rock strata to another with very different properties which requires totally different methods to secure the tunnel. If you read about the history of railroad tunnel building in the US, there are all sorts of examples where a tunnel may start in normal rock, then they hit super hard rock only to hit rock that is basically compacted gravel. One example of such a tunnel is the Brookville Railroad Tunnel, outside Greenwood VA, built in 1856. #2 This is really too broad of a question for a simple answer. Mine engineering is a very broad and detailed field. I know a couple people who got into it. How you secure a mine is like asking how you design a building. It depends on many factors. What type of rock you are going through, how you are drilling the rock, what sort of access do you have for equipment, power available, how hard it is to get supplies to the area, how much money is available, what the intended use of the mine will be, what they want to happen to the mine when they are done, what will be done with the materiel that is removed, etc. |
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Post by the light works on Dec 11, 2015 3:36:03 GMT
#1 Mountains are usually not solid rock. Instead they are layers of different rocks stacked one on top of each other and the worn and weathered over time.. One prime example in the Eastern US is the Sidling Hill Cut for I-68 outside of Hancock, MD. upload.wikimedia.org/wikipedia/commons/3/35/Sideling_Hill_cut_MD1.jpgThe physical properties of the various layers of rock can vary greatly. If you were driving a tunnel though layers of rock like the above pic, you can imaging all the different type of you that you would have to deal with. This is actually a very common problem when people are boring tunnels or mines. They can transition from one rock strata to another with very different properties which requires totally different methods to secure the tunnel. If you read about the history of railroad tunnel building in the US, there are all sorts of examples where a tunnel may start in normal rock, then they hit super hard rock only to hit rock that is basically compacted gravel. One example of such a tunnel is the Brookville Railroad Tunnel, outside Greenwood VA, built in 1856. #2 This is really too broad of a question for a simple answer. Mine engineering is a very broad and detailed field. I know a couple people who got into it. How you secure a mine is like asking how you design a building. It depends on many factors. What type of rock you are going through, how you are drilling the rock, what sort of access do you have for equipment, power available, how hard it is to get supplies to the area, how much money is available, what the intended use of the mine will be, what they want to happen to the mine when they are done, what will be done with the materiel that is removed, etc. that is quite a geologically interesting cut. wonder how it formed that way - is that a runner from a volcanic peak? |
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Post by mrfatso on Dec 11, 2015 8:02:49 GMT
Looks like a regular Synclinal fold structure to me .
The bedding planes which one were horizontal have been concertined by the forces of the Orgeny that created that structure.
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Post by silverdragon on Dec 11, 2015 8:36:35 GMT
Cant remember where, but a single track in the scandeweigian countries was being updated to two lanes via new tunnel. their way to deal with the unstable ground was freeze (via drilled holes) the ground ahead of them and then put in concrete lining after the TBM had passed through.
Unstable and water pressure of 190 psi in the ground water....
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Post by the light works on Dec 11, 2015 15:48:24 GMT
Cant remember where, but a single track in the scandeweigian countries was being updated to two lanes via new tunnel. their way to deal with the unstable ground was freeze (via drilled holes) the ground ahead of them and then put in concrete lining after the TBM had passed through. Unstable and water pressure of 190 psi in the ground water.... I thought freezing was an unavoidable part of Scanawhovian road construction.  |
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Post by the light works on Dec 11, 2015 15:49:42 GMT
Looks like a regular Synclinal fold structure to me . The bedding planes which one were horizontal have been concertined by the forces of the Orgeny that created that structure. the first expectation would be that the hill was pushed upwards, but instead it looks like someone dropped a rock on the ground and it sunk in. |
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Post by mrfatso on Dec 11, 2015 16:41:01 GMT
Think of it more like a crumple zone in a crashed car, as two tectonic plates move together a zone between them is squeezed inwards and form a series of up curving Anticlines and downward curving Synclines.
There are other structure that may be formed like Overfolds, Thrust faults etc.
The Isle of Wight off the south of England is has a large recumbent fold structure caused by the Alpine Oregeny at its core.
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Post by the light works on Dec 11, 2015 16:46:49 GMT
Think of it more like a crumple zone in a crashed car, as two tectonic plates move together a zone between them is squeezed inwards and form a series of up curving Anticlines and downward curving Synclines. There are other structure that may be formed like Overfolds, Thrustfaults etc. yes, but without seeing the cross section, one would guess the hill might have been upthrust. here, the geology is much more angular in its displacement I suspect due to having more igneous rock, and newer strata in general. the only real sedimentary structures we have are coastal, and most of them are very young, geologically speaking. so we will occasionally have two angles of strata showing, but they are usually thrustfaults. |
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Post by wvengineer on Dec 12, 2015 12:24:44 GMT
Think of it more like a crumple zone in a crashed car, as two tecthtonic plates move together a zone between them is squeezed inwards and form a series of up curving Anticlines and downward curving Synclines. There are other structure that may be formed like Overfolds, Thrustfaults etc. yes, but without seeing the cross section, one would guess the hill might have been upthrust. here, the geology is much more angular in its displacement I suspect due to having more igneous rock, and newer strata in general. the only real sedimentary structures we have are coastal, and most of them are very young, geologically speaking. so we will occasionally have two angles of strata showing, but they are usually thrustfaults. My understanding is that the local "mountains" like Sidling Hill are crumple zones. Imagine a stack of multi-colored paper that has the ends pushed together to form multiple ridges. Overtime those upthrust ridges have eroded away until today when the current hills are actually the bottom of the ancient mountains, hence why the layers of strata are curved upwards. Today there is a layer of hard rock near the top of the strata. If you look at the picture it is the dark band that crosses the top terrace step. This layer is the lock that is keeping the whole mountain there. When that layer erodes away, the whole mountain will basically wash away in a geological timescale. Compared to other mountain ranges, the Appalachian mounts are VERY old. They have nearly completely eroded away. What we have today is basically the last stages in the death of a mountain range. Also, when you consider the spacing for the current mountains that represent the valleys between ancient mountains, you can estimate the size of the origional mountains and those mountains would have been ones to dwarf the Rocky Mountains an even the Himalayas. |
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Post by the light works on Dec 12, 2015 15:50:52 GMT
yes, but without seeing the cross section, one would guess the hill might have been upthrust. here, the geology is much more angular in its displacement I suspect due to having more igneous rock, and newer strata in general. the only real sedimentary structures we have are coastal, and most of them are very young, geologically speaking. so we will occasionally have two angles of strata showing, but they are usually thrustfaults. My understanding is that the local "mountains" like Sidling Hill are crumple zones. Imagine a stack of multi-colored paper that has the ends pushed together to form multiple ridges. Overtime those upthrust ridges have eroded away until today when the current hills are actually the bottom of the ancient mountains, hence why the layers of strata are curved upwards. Today there is a layer of hard rock near the top of the strata. If you look at the picture it is the dark band that crosses the top terrace step. This layer is the lock that is keeping the whole mountain there. When that layer erodes away, the whole mountain will basically wash away in a geological timescale. Compared to other mountain ranges, the Appalachian mounts are VERY old. They have nearly completely eroded away. What we have today is basically the last stages in the death of a mountain range. Also, when you consider the spacing for the current mountains that represent the valleys between ancient mountains, you can estimate the size of the origional mountains and those mountains would have been ones to dwarf the Rocky Mountains an even the Himalayas. perhaps a comparison of what the strata in MY local hills looks like will make my point:  |
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Post by wvengineer on Dec 13, 2015 12:04:39 GMT
Just to make sure I am seeing this right, is the strata at something like a 60 degree angle in straight lines?
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Post by the light works on Dec 13, 2015 15:09:38 GMT
Just to make sure I am seeing this right, is the strata at something like a 60 degree angle in straight lines? it is basically heaped up, or bulged up. we do have other cuts that have the strata pushed up in a more or less straight line. I played chauffeur for a geology student in college, who was working on a class project of measuring the orientation of the strata to establish what folded, where. |
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Post by mrfatso on Dec 14, 2015 7:15:28 GMT
I did that kind of independent mapping project in my first year at University, taking a series of dip and strike measurements over a large area of ground, identifying rock types and constructing your own map of the area and identifying the underlying structure.
This is then compared to what the (in my case) the British Geological Survey thinks the structure is and see how similar they are.
Although your student had it lucky if they had you as a chauffeur, I had to use Shanks pony to cover the ground myself.
If the rock strata is at 60 degrees or so it could be a number of structures, without more data it is difficult to tell which one it is, part of one limb of an Anticline or Syncline or part of an Overfold for example. These would relate to the Pacfic plate and American Plate margin.
The Appalchian Mountains are part of the same Orgeny as made the Scottish Highlands, and are ancient they formed due to the closure of the Iapetus Ocean.
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Post by the light works on Dec 14, 2015 14:27:53 GMT
I did that kind of independent mapping project in my first year at University, taking a series of dip and strike measurements over a large area of ground, identifying rock types and constructing your own map of the area and identifying the underlying structure. This is then compared to what the (in my case) the British Geological Survey thinks the structure is and see how similar they are. Although your student had it lucky if they had you as a chauffeur, I had to use Shanks pony to cover the ground myself. If the rock strata is at 60 degrees or so it could be a number of structures, without more data it is difficult to tell which one it is, part of one limb of an Anticline or Syncline or part of an Overfold for example. These would relate to the Pacfic plate and American Plate margin. The Appalchian Mountains are part of the same Orgeny as made the Scottish Highlands, and are ancient they formed due to the closure of the Iapetus Ocean. It would have been a long project - I think the outcroppings we measured covered 30 or 40 miles range. |
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