Deep Mining Under Railroads
Deep Mining Under Railroads
(OP)
Is there any requirement to stabilize deep mine workings under railways in Pennsylvania?
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Deep Mining Under Railroads
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RE: Deep Mining Under Railroads
RE: Deep Mining Under Railroads
The mine workings were originally "room and pillar" which were partially extracted according to the detailed mine map. The air-rotary borings drilled across the site encountered mainly broken bedrock at the mine level with 100% air loss indicating small voids throughout. A down-hole camera was only able to observe an approximate 1-foot void in one of the borings, but could not get down to mine level in the rest of the borings due to collapsing after drilling at the mine level. 1 boring encountered intact coal, which could mean full height voids (up to 13 feet) in the area because of the pillars remaining and roof rock possibly not collapsed. Cover is only approximately 75 feet, so a moderate to high risk was assigned based on the depth to the mine and current condition of the void space.
Grouting of the mine is currently recommended unless a more detailed investigation shows that no full height voids exist and if the estimated settlement from subscidence in partially collapsed mine workings is within tolerable levels.
I am just trying to find out if the client has no choice but to stabilize the mine based on any railroad regulations. Thanks for your interest and any help you can provide is appreciated.
RE: Deep Mining Under Railroads
J
RE: Deep Mining Under Railroads
Spread the topside rail-to-rail distance apart a bit further than the standard in-yard separation; then use the increased distance between every two adjacent rails (and the switches/turnouts) together with a thicker, more resilent grade or underlayment to reduce the average weight-per-sq-yard of the railroad system.
So, rather than fill the old mine shafts up with concrete+ grout to increase the average ground strength, reduce the average surface loading of the rail cars above ground so the 74 feet of overburden can manage the average load on each rail.
Alt: manage the cars so no two loaded trains are ever parked side-by-side of each other. (Probably not possible, but its only to bring up in a meeting so the client can smile for a few minutes.)
RE: Deep Mining Under Railroads
Loading is not an issue when it comes to potential mine subscidence; unless it was some astronomical surcharge. When the mine collapses, it's merely the mine level materials wearing away until failure.
RE: Deep Mining Under Railroads
RE: Deep Mining Under Railroads
The problem I am having is not with what to do about the mine. Grouting appears to be the option to go with at the moment; although, stabilization may not even be required based on further investigations and theoretical settlement calculations if no large voids are present. I am merely looking for guidance on railway regulations on the subject of mine stabilization. I know railway regulations are usually over-conservative and thought no matter what the size of the void or condition at mine level, it has to be stabilized. I also posted this question in the railroad engr section, where no reply has been given so far.
Thanks again for the continued interest in my issue.
RE: Deep Mining Under Railroads
RE: Deep Mining Under Railroads
This somewhat reminds me of folks worrying about the loads from truck traffic on highway fills. In most of those cases the weight of the trucks has very insignificant effect on settlements. The same probably would go for your RR yard loads. Your weights you might more likely need to think about are those soil and rock weights above the former mine workings. I've experienced measuring the effect of loaded freight cars on culverts under the ties and there is significant spread of load under loaded freight cars and locomotives are even lighter (than the cars I worked with).
Time also is important. How long ago was that mine worked? The more time involved, the less likely there will be future RR yard problems.
What does it cost to re-set track in case it tilts or has a roller coaster vertical profile? You could bury this cost in annual maintenance expenses. RR guys easily can drag a whole long section of track, with ties attached, off an area, re-grade it and drag it back. That would be in a real bad case of settlement only.
If you are still concerned and want to do something, consider running a rolling surcharge of earth across the site. I'd think about a "windrow" maybe 10 feet high and 20 feet wide on the top (any length) being shoved across the site with a dozer or a backhoe sitting on top. You could monitor the effect with simple settlement platforms. Moving fill this way is cheap, probably much cheaper than the grouting option. It would put much more load (pressure) on that mine than any bunch of loaded freight cars.
Dig a hole at one corner of the site to get this surcharge, move it over the site in a "U" pattern, bringing the earth back to its source after traversing the site. You would not have to wait at any location, since this is something like compacting earth with a roller.