CSSHEGEWISCH In a footnote in Jerry Pinkepank's two-part article in TRAINS in the mid-60's about the Detroit and St. Clair tunnels (A Tale of Two Tunnels) is a comment about what happens when the surveyors get sloppy about their work. Apparently, the shields used to bore one of the H&M (now PATH) tunnels were allowed to drift out of line and there is a reverse curve in the tunnel where the shields had to be turned to get back into alignment.
A tale of two tunnels 2 Trains, October 1964 page 40 the Detroit and St. Clair river tunnels ( CANADA, GT, MICHIGAN, NYC, ONTARIO, "PINKEPANK, JERRY A.", TUNNEL, TRN )
Hmm - don't think I have those 2 issues yet. Will have to get them, if only for this reason. Thanks for mentioning it !
- Paul North.
mudchicken Back to QueCreek;
Back to QueCreek;
Thanks, MC...for the comprehensive answer on said subject.
100% totally agree, if the surveyors of the past had not done accurate work....anything used now to read from their remaining records...{maps}, would have been useless.
Mine surveying was in some cases not very easy work....Depending on the seam of coal. Example: My dad helped with survey work back 60 some years ago and he mentioned of doing some work where the "roof" was just 2' in height....
Item: The location of the rescue bore to the miners at Quecreek was located just a very short distance from a farmers lake {pond}....Fortunately, it was where it was and not where they needed to drill.
Quentin
In a footnote in Jerry Pinkepank's two-part article in TRAINS in the mid-60's about the Detroit and St. Clair tunnels (A Tale of Two Tunnels) is a comment about what happens when the surveyors get sloppy about their work. Apparently, the shields used to bore one of the H&M (now PATH) tunnels were allowed to drift out of line and there is a reverse curve in the tunnel where the shields had to be turned to get back into alignment.
QM:
QueCreek was a very old mine. From the adit, more than one firm (Three, IIRC) had worked the area. Each of those mine surveyors had done conventional work for many years, built off what the previous surveyor had done. Each had used the preceding survey control of the others to traverse into and through the maze that is a mine. If any of those preceding mine surveyors had done his work improperly or not checked the work of the surveyor before him, the location of the trapped miners would be open to question, especially on an open ended traverse (as opposed to a loop route) into some of the further reaches of the mine. If there was a "bust" in there somewhere (math error, instrument error, cummulative error or any of host of random or systematic errors) - those miners would be in trouble with a lesser margin of safety before anything caved-in.
GPS, used properly, is a nice tool that can be used quickly with a high degree of precision. (used badly in conjunction with a poor grade GIS and you have Darwinian knucklehead candidates driving onto the tracks because "the GPS [should be GIS] said turn here)...GPS was used to locate and orient monuments those earlier mine surveyors had tied down using the old conventional methods. GPS got them to a point where they could drill a resue shaft (conventional methods could have done the same thing a little slower) to A KNOWN POINT x-Y-Z below. If those original surveyors had not done their job well, that rescue shaft may not have come out where it did in the room below (it might have gone through a wall or other solid rock and made things worse).
If those mine surveyors had not done good work and done a good job of documenting & made available for others to follow in their footsteps what they found and measured, the later GPS would not have been of any use at all.
[ Common gripe among surveyors is that the general public sees surveyors in the field with their equipment, but has no clue as to all the myriad other things that he/she does as part of the profession which usually takes 2-3 times as long to do as what folks see in the field]
...still see a pendulum in a shaft strung by piano wire damped with the pendulum in a bucket/barrel of oil just enough in buildings and mines today to be reminded of what those folks did long before me.
MC, PDN, JCH...
I ran across a book some months ago (which I cannot, for the life of me, find in what I call my "well organized library"-but what others unkindly call my "book strewn living room") entitled, "The Measure of All Things". It's about the survey crews sent out to measure the line of longitude across France that would be used to determine the circumference of the globe and, from it, the length of the meter. All sorts of things that I'm sure you guys have dealt with: faulty equipment, bad assistants, missing landmarks, war with Spain, the French Revolution-you know, the usual stuff...
I'm sure MC will get to this -- but in the meantime he has my deepest sympathy; new push button electronic toys are a pain...
The only way that I know of to set a good baseline at the bottom of a central shaft is the two heavy pendulums trick Paul alluded to above. First you set a very accurate line over your mountain or whatever, including the central shaft. Then you set in the central shaft a pair of pendulums which reach to the bottom (they are usually damped at the bottom -- a bucket of oil, warm wax, whatever) and determine a) the exact location of each pendulum with respect to the proposed centreline and b) the exact angle which the line between them makes with that proposed centreline. The more accurately you can do this, the happier everyone will be. This part of the job is tedious, and accuracies of better than 1 second of arc are required -- but can be achieved with care (and, as MC noted, a good instrument in good shape, properly calibrated). Then you go to the bottom of the shaft, and, since you know exactly where the pendulums are, and what the angle of the line between them is to the centreline you want, you can carry on. Extending the line below takes the same devotion to path of precision surveying as measuring the line above did...
One reason I've always loved surveying, though, is just that need for care and precision -- and the tremendous satisfaction that comes from having everything check out right when you are done!
War stories: I once had the job of running a first order level line from a known benchmark on the old CV railroad up to the top of a hill -- a matter of about 5 miles. No big deal, but about 4 miles up was an Interstate highway, which had a good second order benchmark the DOT had set up. A nice check on my work, I figured. But after the arithmetic was done, my shots on that benchmark and the DOT's value for it were about 10 feet off. Consternation. Come to find out the DOT had made an arithmetic mistake... and then just 'adjusted' the bad line to close at the other end! Grrr...
mudchickenThe IT Department is here to deGauss me
Don't let them over deGauss you......
Mudchicken - The original question was about setting a good baseline in the bottom of a central shaft so diggers can bore from the middle towards the outer portals. Any ideas how to get an accurate baseline where there is no room or sky.
Q:
The IT Department is here to deGauss me and load new-used CADD software that I have no training to use on my machine (more push da button and see what happens). I will answer you in a while or after I get home.
mudchicken(4) The QueCreek disaster was a testament to the unheralded mining surveyor, not GPS. (they've come a long way from the old wax rings.)
Mudchicken.....Could you address for us laymen a bit farther your meaning of the above statement....
"Most survey work is doing precise work in impossible conditions." Hey, I like this guy already !
You know, I thought I was about the only one who had that view of things, and generally don't broadcast it - might be bad for morale, you know. Nice to know there's someone else out there who shares that jaundiced view of the world. But better to recognize reality and cope with it than to do the ostrich thing and stick our heads in a hole in the ground . . . oh wait, we're discussing tunneling here, aren't we . . . well, you know what I mean anyway.
Not to digress into "war stories" too far, but it pertains: About 2 years ago, Warren - the foundation contractor's layout man on a big and important project nearby (hospital wing/ tower addition with some odd angles in it) - questioned the accuracy of the "baselines" we'd set up for him. Much additional field work and checking later revealed he had 2 problems: 1) His instrument was out of calibration; 2) He was using wall thicknesses to set column lines, not the dimensions between the column lines - which to be fair, were not clearly set forth on the plans (architects more interested in "statements" than structures - another bane of our existence, but that's not a railorad topic anymore).
Thanks for sharing your view of this from west of the Mississippi.
jeaton Just waitin' for the Mudchicken to 'splain GPS and survey results using the same...
Just waitin' for the Mudchicken to 'splain GPS and survey results using the same...
(1) If you're using GPS in a tunnel by itself, you are not going to get results. (It never ceases to amaze me what real estate agents, used car salesmen and other such nitwits think GPS technology is and what it does.)
(2) Engineers and GPS don't mix. (want state plane coordinates, don't know the difference between grid & ground....can't tell you the difference between accuracy & precision either)
(3) You can screw up GPS by just missing a decimal point in the scale factor. If you don't know what you are doing and do not know how the technology works, you are doomed to never be much more than a poor technician/ mechanic.
(4) The QueCreek disaster was a testament to the unheralded mining surveyor, not GPS. (they've come a long way from the old wax rings.)
(5) The old survey instruments were only as good as the circular dividing engine that scribed the movable and fixed plate (upper and lower) circular motions plus the machining. (I own an 1873 Gurley Engineers Transit and am still on the lookout for a Gunter's Chain - Somebody two owners before me bought the transit to lay out grades and ditchlines with it in the 1960's - PDN might see the humor in using an engineer's transit to establish grades) - Only a geodicist could own a Parkhurst Theodolite with the huge horizontal and vertical circles that required a herd of people to move and set up. Railroaders and tunnelbuilders settled for smaller and less precise transits for their work. The equipment was still better than what the local land butcher used. They made up for the lack of precision by improving and rigidly adhering to procedure which meant tedious field work. They generally got the desired results. Most survey work is doing precise work in impossible conditions.
(6) If you did your prep work properly before you began your tunnel (lots of long backsight night work) and projected your line over the hill, accounted for the shortcoming of your optics and equipment (kept it adjusted, clean and in tolerance), plus treated the project with studied respect - you generally got the desired results.You ought to see some of the nonsense that happens when a construction contractor keeps a cheap and none to bright construction survey technician around a large project.
In theory, a compass would work underground as you point out, at least for short distances. The magnetic declination = difference between the magnetic pole and geodetic north or the center of the Earth's rotation is known pretty well and can be adjusted accordingly. Since each degree is worth about 1.75 feet ( 1 ft. 9 in.)at 100 ft. away, then reading directly or estimating between the graduated marks to within a half- or quarter-degree (15 minutes) would keep the accuracy to within around 1 ft. or 1/2 ft., respectively, for each 100 ft. of distance.
But at a mile away from the intermediate shaft, that 1 degree of uncertainty would amount to about 92 feet (50 feet or 25 ft. for the smaller divisions above), so long before that point the compass readings would be too unreliable to assure that two bores being drilled towards each other would actually match up tolerably well.
Practically, a magnetic compass is subject to deviations from or caused by the presence of magnetically capable materials nearby, which are difficult to adjust for. Know of any tunnels that are bored without a lot of steel tools, equipment, bracing, and electric lines (with magnetic fields of force) in them ? if not, then we've got to find another way to measure and closely control the direction and dimensions of the tunnel boring operation.
Why wouldn't a compass work underground. The magnetic lines of force are generated in the molten core of the earth and have to travel through miles of rock to reach the surface. I will grant that they are weaker as you are closer to the axis between the poles.
For any person who has done something heroic and very public it is very common for them to get this period of euphoria after the event and then fall into a deep depression. Being a person who has dealt with deep depression I myself would avoid media attention and keep my life as normal as possible if I ever did something heroic that ended up on TV and in the newspapers.
Modeling the "Fargo Area Rapid Transit" in O scale 3 rail.
Paul_D_North_JrSadly, the surveyor who ran the GPS to guide the rescue committed suicide a couple years later
You know Paul, that is a strange phenomenon, and has happened in the past....Know not how many, but remember one of the fellows that brought up one of the little girls from down in a well....oh some years ago....committed suicide too.
Trivia: My home back in Pa. is just about 5 miles from the rescue site near Quecreek. We were there a day or so after the rescue. it is a marked site now and still visited by many.
The photo of my avatar {of our car}, is parked at a restaurant and that is just about 3 miles from Quecreek.
That was the Quecreek Mine wall collapse, about 6 or 7 years ago. GPS was indeed used for the rescue, but only on the surface, to guide the rescue drills. And yes, the GPS was "right on" - or at least close enough - for that purpose. But then, ithe GPS should have been - it was running from the surface (not underground); the distance to bore was only 240 ft., not thousands of feet or miles; and even if it was a foot or two off, they were drilling to intercept a mine shaft, a comparatively big target - not trying for accuracy of less than an inch or so.
But the fellow running the GPS on the surface had to know where to aim the rescue drills at, and that was based on accurate underground surveys by conventional methods. Ironically, the initial collapse was really caused by the poorly mapped adjoining mine, which had since closed and flooded - the miners inadvertently drilled into it and flooded their own mine.
Sadly, the surveyor who ran the GPS to guide the rescue committed suicide a couple years later. I never saw a definite reason, but the consensus seems to be that a combination of the glare of publicity and notoriety for a guy who was pretty private by nature, and some strains and friction with the miners who were actually underground, was more than he could bear. A tragedy from an actual heroic event - just too bad.
Modelcar jeatonJust waitin' for the Mudchicken to 'splain GPS and survey results using the same I know of 9 miners that GPS helped save their lives over in southwestern Pennsylvania....Helped to locate the drills up on the surface that would push a bore down to effect their rescue....! They were in fact brought out of that bore {240' deep}, that broke right thru where they were trapped.
jeatonJust waitin' for the Mudchicken to 'splain GPS and survey results using the same
I know of 9 miners that GPS helped save their lives over in southwestern Pennsylvania....Helped to locate the drills up on the surface that would push a bore down to effect their rescue....! They were in fact brought out of that bore {240' deep}, that broke right thru where they were trapped.
The target for the bore might have been a fairly good sized room, and so that would be an effective use of GPS as long as the mine drawings were accurate.
"We have met the enemy and he is us." Pogo Possum "We have met the anemone... and he is Russ." Bucky Katt "Prediction is very difficult, especially if it's about the future." Niels Bohr, Nobel laureate in physics
NP Red Thanks, I think this is the answer I overlooked. I didn't think the width of a 20ft shaft would be accurate enough to get a good baseline but if after boring 100ft or so you could drill down a 6 inch well and get a accurate point either by a plumb bob or better yet a vertical laser transit gizmo.
Thanks, I think this is the answer I overlooked. I didn't think the width of a 20ft shaft would be accurate enough to get a good baseline but if after boring 100ft or so you could drill down a 6 inch well and get a accurate point either by a plumb bob or better yet a vertical laser transit gizmo.
You don't need the shaft from the surface to set a base line and it is not employed.
Not said is that mine surveying encounters even more difficult problems.
RWM
Paul_D_North_Jr Finally, in lieu of intermediate shafts, a couple of essentially narrow wells - just wide enough to accomodate plumb bobs and assure that a vertical plumb bob will not touch the sides - could be drilled down to the tunnel elevation. This is similar to the Hoosac Tunnel method, but much farther apart - more like multiple intermediate shafts. Then, connect those defined points with a traverse down in the tunnel, and proceed from there.
Finally, in lieu of intermediate shafts, a couple of essentially narrow wells - just wide enough to accomodate plumb bobs and assure that a vertical plumb bob will not touch the sides - could be drilled down to the tunnel elevation. This is similar to the Hoosac Tunnel method, but much farther apart - more like multiple intermediate shafts. Then, connect those defined points with a traverse down in the tunnel, and proceed from there.
Paul's pretty well got it. Of course, GPS doesn't work underground -- and doesn't approach the accuracy required to set up a long bore.
The main thing, though, is patience... and care... and more patience... and more care. It isn't so much the instrument, although modern instruments make life much much easier, as it is technique and care. I still have my 1888 30 second Gurley transit -- in fact I was just using it today! -- and compared with a modern total station it's a bear to operate -- but with care I can achieve 1 second accuracy from it. Just take time...
You might be surprised . . .
And the temperature, humidity, and density of the air in the tunnel, the gravimetric effect of the mountain's mass and any denser-than normal rock in it - like ore bodies - on the plumb bobs, upswelling of the rock in the tunnel when its no longer confined under load, etc.
One thing I didn't mention was that because of the close quarters and heavy traffic, the survey points are usually put in the roof of the tunnel - instead of on the floor, where they would be quickly disturbed or damaged - using short metal stakes or shafts developed for that purpose that are commonly called "spads".
But what eliminates many errors are just good field procedures. One of the simplest - in a continuous series of repetitive measurements - is to measure an angle the first time with the telescope in the normal position. The next time, measure it with the telescope upside down - that cancels out most horizontal asymmetry in the optics. Likewise, using different portions of the graduated circle (think of the part that looks like a simple protractor) that is used to measure the angle - from one measurement to the next - tends to cancel out any asymmetry there. Making sure the instrument is calibrated before starting is important, too.
It's not rocket surgery, but like any technical field of endeavor, it has its principles and limitations, which have been developed by a lot of smart guys over the years. The prudent and wise practitioner knows and respects them and works with and around them as needed. As ndbprr indicated, with care you can do seemingly amazingly accurate work with a good instrument.
Thanks, Paul. Now talk about refraction correction ...
It's a very specialized aspect of tunnel and underground mining surveys, which are already pretty unusual by themselves, and require specialized instruments - mainly capable of extreme vertical angles. It starts by running a conventional but highly accurate survey control traverse or network from and between the ends of the tunnel over the top of the mountain to the intermediate shaft. There are then at least a couple of ways:
The shaft has a width - not much, but some - typically in the 10 to 20 ft. range. The survey instrument - think of a typical surveyor's transit, though actually more sophisticated instruments would be used, such as theodolites - can be set on one edge of the shaft at the top, and then below the other side of the shaft at the bottom. That horizontal distance - even over a long vertical distance - provides a short "baseline" to use as a starting reference line for all of the angle measurements. Alternatively, the instrument at the bottom of the shaft can sight on a star or other astronomically fixed point to use as a reference point. Actually, that would be better, because the baseline would be that much longer, although care has to be taken not to let the vertical angle get too close to 90 degrees or even that will lose its usefulness.
What was done at the Hoosac Tunnel in western Massachusetts in the mid-to-late 1800's was to suspend 2 very heavy plumb bobs over 1,000 ft. down the shaft - one on each side - into small buckets of oil to damp out any swaying motions. That shaft might have been as much as 30 ft. across. Those 2 plumb bob lines also defined a horizontal line that was used as the reference line for all angle measurements.
The guys at Hoosac (actually one was a professor, as I recall - see the definitive book on it, A Pin-Point of Light) made literally over a thousand measurements and readings off those 2 plumb bob lines to establish the control line down in the tunnel. The laws of statistics and probability say that when you do that and use the "average" result, it will be highly accurate - any random errors will cancel out, as long as the "systemic" errors are anticipated and accounted or compensated for accordingly. That the Hoosac Tunnel "holed through" within less than an inch of deviation (as I recall) says that they did it all extraordinarily well, and that the theory worked.
The same technique - making many measurements and averaging the results - would also be used with the surveying instruments to carry the reference line down the shaft. For example, when the U.S. Coast & Geodetic Survey would run "control traverses", they would typically measure each angle of the polygon something like 32 times - on a cold winter night, too, so there would no distortion from sun-induced heat wave shimmer and the like during the day.
High-end survey instruments have been capable of direct readings to within of - say, 5 seconds of arc - for many decades now (recall that there are 360 degrees of arc in a full circle, each degree having 60 minutes, and each minute having 60 seconds). To put this into perspective, at a mile away from the instrument, that 5 seconds of arc amounts to about 0.13 ft. = 1-1/2 inches. With repetitive measurements and averaging the results, a final value on the order of 1 second of arc is attainable - that is about 3/8" at a mile away - and even finer than that can be achieved and relied upon.
Better yet, if 2 (or more) intermediate shafts are sunk and connected by even a pilot tunnel, that will provide a baseline that is a significant fraction of the tunnel's length - like 1/4 to 1/3. With that, accuracy of 0.01 to 0.02 ft. = 1/8 to 1/4 inch should be easily obtainable.
Prudence would indicate that if possible, the middle portion of the tunnel not be fully widened or finished until it is "holed through" to at least one of the ends, so that an survey traverse with a long baseline could be run to check the alignment, which would make it more accurate. Leaving some tunnel work to do yet would enable some adjustments to be made if necessary.
But as a practical matter, for any current rail speeds - up to the 200 MPH range - even deviations large enough that surveyors would view them with horror can be easily accomodated by the track structure and alignment and train operations, and no one would be the wiser or care, as long as the resulting adjustment is spread out over a long enough distance. After all, in tunnels long enough to need or benefit from intermediate shafts, even the curvature of the earth has a noticeable effect !
Hope this is informative. Let's see if anyone else can add to it.
Doing long distances of surveying, I find it difficult to understand what can be in place to prevent errors of small value from becoming accumulating larger errors.....And especially inside a bore underground.
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