I'm not sure why they built the trestle that way. Typically, there would be diagonal timber bracing from bent to bent on the outer pilings, and also across the width of each bent, on each side of each bent. I assume that this visible part of the trestle has never been filled, and that they drove the pilings into existing soils, so there would be no need to compact that soil.
But going back to the creation of new fills by constructing a fill trestle: I think there is a good chance that this type of fill was left uncompacted with the idea that it would just settle with the rain, and that would be good enough. I have seen photos showing the process called "jetting" whereby a high pressure water hose was used to break up the fill chunks and make the fill material flowable. That has long been considered to be a form of compaction. But it leaves the soil fully saturated, and such a degree of saturation means that the soil is too wet to properly compact with horses, sheeps' foot rollers, vibratory drum rollers, steel track dozers, or vibratory plate compactors.
To use any of means of compaction, the saturated soil would have to be left to dry out for many months. And even then, the whole height of the fill would be in place, and any compaction would be limited to only the top couple feet. Proper compaction would require compacting one 6" fill layer at a time. So if the fill was 60 feet tall, it would require adding and compacting the fill in one layer at a time, so that would be 120 individual layers of fill.
EuclidFor new track, the fill trestle was of relatively light material because it did not have to last long, and it was typically only supporting narrow gage dump cars and locomotives.
The following crude sketch shows what they did here in 1911 to grade separate the mains through our downtown. Roughly raising the track 10 feet, and dropping the pavement 5.
Based upon other items present in the source image, I'd guestimate these timbers about 16" square.
Absence of cross bracing would seem to accomodate compaction?
Convicted One I believe that one of the things that took me off on a tangent was when someone posted earlier about burying a wooden "trestle" as part of an engineered fill design, the vision that came to mind was of a trestle sporting horizontal and diagonal braces between the verts. And my biggest concern was with how those braces would span, and stand in resistence to settling and compaction. What I've since seen, "trestles" that more resemble rows of 16" square timbers driven vertically into the ground like piles, each row spanned by a similarly dimensioned horizontal "header" that the track bed rests upon....gives me less reservation.
I believe that one of the things that took me off on a tangent was when someone posted earlier about burying a wooden "trestle" as part of an engineered fill design, the vision that came to mind was of a trestle sporting horizontal and diagonal braces between the verts. And my biggest concern was with how those braces would span, and stand in resistence to settling and compaction.
What I've since seen, "trestles" that more resemble rows of 16" square timbers driven vertically into the ground like piles, each row spanned by a similarly dimensioned horizontal "header" that the track bed rests upon....gives me less reservation.
I seem to recall a section of the original Santa Fe in callifornication has a fill on top of a layer of straw so the entire fill floats.
I was rebuilding a city street a couple of years ago and found a series of logs sitting cross-wise to the road in a low (soft) spot.
northeasterEuclid: Back in the 1960's, when I was young and living on a hill farm in remote Vermont, my Road Commissioner described to me how he would fix a dirt road going through a swampy section: cut down a bunch of spruce trees and spread the branches along the wet road bed and cover it with a gravel/soil mix. The new surface would "float" on the bed of spruce branches and do just fine.
Right up to the time that a heavy load gets on top of the floating surface and sinks it.
Never too old to have a happy childhood!
northeaster ...how he would fix a dirt road going through a swampy section...
When they were building I-81 through my area, they had a spot that was swampy, but apparently thought they could deal with it.
There's still a large piece of construction equipment buried in the muck...
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Euclid: Back in the 1960's, when I was young and living on a hill farm in remote Vermont, my Road Commissioner described to me how he would fix a dirt road going through a swampy section: cut down a bunch of spruce trees and spread the branches along the wet road bed and cover it with a gravel/soil mix. The new surface would "float" on the bed of spruce branches and do just fine.
Compaction is important for building hard surfaced roadways because their asphalt or concrete pavement will break up with any differential settlement which is bound to occur with uncompacted fill. It may be somewhat less important for railroads because their ballast and trackwork spreads the wheel loading out over a broader area than road loading. Compaction is vital to building foundation footing support, and ultra-critical to dam construction. Proper compaction is performed by filling in relatively thin layers of say 6”, and then compacting just that layer. Then that process is repeated one layer at a time until final grade is reached. The uncompacted layer is called a “loose lift.”
Compaction cannot be properly performed by simply adding enough weight to the height of a high fill, such as using a heavy locomotive to run over track laid on say 20 feet of loose fill. The result will be the greatest compaction at the top and successively less compaction as the depth increases. Even if you used a heavy enough locomotive to achieve adequate compaction at the base of the fill, it will be progressively over-compacted in the higher regions of the fill. The over-compacted fill will slowly rebound over time and raise the finish grade.
Another factor is the penetration of ground freezing in winter. As the ground freezes, its water content expands and increases the fill volume. As the frost penetrates deeper, the finish grade rises with a force that will lift buildings, trains, and highway traffic higher. The seasonally rising and falling soil may not do so uniformly due to variations in the frost action due to variations in the ground cover or soil type. In any case, soil that rises in winter will be “fluffed up.” Then as it resettles in summer it will not return to its original compacted density that it had achieved by being properly compacted with equipment.
The lifting and settling of frost affected soil will also vary as the soil and its conditions vary. So, the lifting and falling finish grade may not be uniform over a given area. That is why you see wooden shims driven under the tie plates of railroad track in winter to lift the rails in order to match their degree of frost lift that occurred nearby. So, buildings are not allowed to have their foundation footing supported by soil that will freeze from winter frost penetration. But, roads and railroads will rise and fall with the ground frost action.
There is another problem for roadbed fill stability besides compaction. That is the type of soil under the intended fill. Pioneering railroad routes encountered lots of peat bogs and similar organic soil. These soils never stabilize. Not only are they fundamentally un-compacted in situ, but they are also incapable of being compacted. So, if you place a fill on these organic soils, the weight of the fill alone is likely to cause settling by displacing the underlying organic soil. The organic soil will push out at each side and heave upward in response to the weight of the fill. It is like stepping on toothpaste.
The only way to build a successful fill on these organic soils is to remove them down to stable sub-soil and replace them with good fill material. This is called soil correction. It can add considerable cost because the organic soil might be 10-40 feet thick. Furthermore, removing the organic soil often requires digging in water because organic soil is often found in boggy areas. And then once the organic soil is removed, you have open water to receive the new proper fill.
Filling the good material into water makes it impossible to properly compact it. Certainly you can’t fill in lifts and compact each one, because it would require working under water. The only way to overcome this problem is to fill into the water with the most ideal granular material. This type of material will displace the water as it falls into place and become stable as the dry fill adds weight as it is place atop the wet fill.
This type of soil correction was mostly out of the question in the 1800s. So the new fill was simply laid on top of the organic and saturated soil. When the fill sank, more was added. Generally a lot of earthmoving continued after the railroad was built. Dirt was hauled to low areas on trains of flatcars and dumped off the sides. When the steam shovel era dawned, the steam powered Lidgerwood Unloader was invented. It was a big cable winch on a special car that dragged a sort of “V” plow down the decks of a train of flatcars, and the plow pushed the dirt off of the cars on each side.
With original railroad beds, there are stories of railroad companies trying to stabilize sinking fill by dumping logs and trees into the morass until the sinking stopped.
Murphy, I was 28 in 1960 and would work for Santa Fe until 1990 when I was offered a buyout that was so good, I could not refuse. But I would do it all again if I were young once more.
diningcar The BNSF Southern Transcon is currently the fastest and most reliable route between Pacific water and Chicago; and it became this way by many changes from original construction; like Abo Canyon recently. Without a doubt the greatest contributor was the Williams - Crookton line change in the Arizona mountains in 1959 -60. The original 1882 construction was 49 miles of single track, with a second track created (in steps) in the 1920's. Some of the segments had 2.6% grades and curves of up to 10 degrees. It was a 20 MPH operation in many locations. The relocated line was 44 miles in length, with maximum 1% grades and one degree curves. To accomplish these parameters there were rock cuts up to 110 feet deep, with the longest being 13,000 feet. The highest fill was 122 feet and the longest was 6000 feet. The design also avoided slack action. From Williams Junction the line descended 32 miles on 1% grade where it intersected a 0.85 % ascending grade. This was designed with a 10,000 foot vertical curve making the change .085 per 100 feet. It was superelevated with spirals on each curve end which would permit 70 mph freight trains and 90 mph passenger trains. The most amazing thing is that this was all accomplished in sixteen months. The contractor - Morrison-Knudsen - worked two nine-hour shifts six days a week. The first train - Santa Fe's The Chief went over the line on December 19, 1960. I had the honor and pleasure of being one of Santa Fe's engineering technicians who set all the stakes and control points for the contractor.
The BNSF Southern Transcon is currently the fastest and most reliable route between Pacific water and Chicago; and it became this way by many changes from original construction; like Abo Canyon recently. Without a doubt the greatest contributor was the Williams - Crookton line change in the Arizona mountains in 1959 -60.
The original 1882 construction was 49 miles of single track, with a second track created (in steps) in the 1920's. Some of the segments had 2.6% grades and curves of up to 10 degrees. It was a 20 MPH operation in many locations.
The relocated line was 44 miles in length, with maximum 1% grades and one degree curves. To accomplish these parameters there were rock cuts up to 110 feet deep, with the longest being 13,000 feet. The highest fill was 122 feet and the longest was 6000 feet.
The design also avoided slack action. From Williams Junction the line descended 32 miles on 1% grade where it intersected a 0.85 % ascending grade. This was designed with a 10,000 foot vertical curve making the change .085 per 100 feet.
It was superelevated with spirals on each curve end which would permit 70 mph freight trains and 90 mph passenger trains.
The most amazing thing is that this was all accomplished in sixteen months. The contractor - Morrison-Knudsen - worked two nine-hour shifts six days a week. The first train - Santa Fe's The Chief went over the line on December 19, 1960.
I had the honor and pleasure of being one of Santa Fe's engineering technicians who set all the stakes and control points for the contractor.
That first train went over the line the day I was born.
Thanks to Chris / CopCarSS for my avatar.
As you noted, dealing with settlement of a fill underneath a railroad is easier than dealing with settlement under a paved road. I have a vague recollection reading that fills under RR tracks take about 5 years to fully settle.
OTOH, I do remember seeing a picture of an NP Yellowstone lying on its side with explanation that it was being used to help compact a filand tipped over when passing a soft spot. A million pound steam locomotive could be counted on to produce a robust vibration of he subgrade.
Convicted One And, I'd think that the framing members would really interfere with compaction. Isn't "compaction" the alpha and omega of site prep?
And, I'd think that the framing members would really interfere with compaction. Isn't "compaction" the alpha and omega of site prep?
Not in the 1910's and earlier. I don't believe compaction wasn't really a common practice until the 1930's.
Compaction does two things: it reduces initial settlement, and it increases soil strength. I'm not sure how well the strength part of that was understood prior to the genesis of modern soil mechanics in the 1920's. The settlement piece was probably better understood but just not that critical for railroad track.
I recall reading the following claim in some engineering text, although I can't recall which one and I can't vouch for it's accuracy:
Railroad engineers noticed early on that high fills across a valley would develop a sag in the middle over time, as the highest part of the fill (in the middle) settled more. They responded by building fills with a camber, so that it would eventually settle into a smooth surface. (Yes, there probably was some differential settlement... In the days of 20-man section gangs, it was no big deal to occasionally tamp up the low spots.) This worked fine for gravel roads as well. However, as paved rural highways became more common, this approach did not work so well, as the pavement would crack when settling. So highway engineers, taking advantage of new equipment that hadn't existed before, adopted compaction as a standard practice.
Dan
Now I'm starting to wonder if perhaps in those documentaries where you see an imported fill earthen dam start to fail with a small trickle just before the deluge, if perhaps there might be a rotting wooden trestle nested within?
I'd imagine there was a sort of a natural compaction of the dirt, falling (at first) some 100' in some cases.
I've seen pictures of the process as well, but don't recall where.
EuclidAs such, gradual settling will occur. When it does, they just haul more fill to the site and build up the the settled areas. Therefore, many fills are being gradually perfected over time.
I found a wonderful picture of them performing the trestle-fill operation in my own town back in 1911 when the mains were grade seperated. Unfortunately I do not hold the rights to said picture, and do not want to set off the IP alarmists.....but it's a great picture showing the fill operation in progress.
SO yeah, it obviously was "done that way"...but again I personally don't have a lot of confidence that the rot, the settling, and the refilling will happen at uniform rates. Heart wood rots differently from the layers around it in my experience, open grain versus closed, etc etc too many variables.
But, as I mentioned earlier, most of the "bouncing track" instances that I have witnessed personally, are on those raised embankments....particularly where they abutt bridges and other viaducts....so perhaps those buzzards ARE coming home to roost.
And it never really ocurred to me previously why when I periodically see the thermite crews at work, it was usually on the raised embankments right next to one of those bridges. So, this is a definite "ah haaa" moment for me.
Convicted One Murphy Siding , and as that slowly happened, the fill would work it's way into the voids. If I was a deep pocket, I don't know how cozy I would be making the assumption that the settling and filling would happen uniformly?
Murphy Siding , and as that slowly happened, the fill would work it's way into the voids.
If I was a deep pocket, I don't know how cozy I would be making the assumption that the settling and filling would happen uniformly?
The filled dirt would work its ways into voids left by rotting timbers over time. But it is not much of a practical problem. Even if a void forms, that does not mean that gravity will readily fill it with fill dirt from above, and work the void upward like a sink hole that finally breaks through the surface.
Soil that has filled around the pole that evenually rots has a fair amount of bridging ability, so many formed voids will simply remain undisplaced with setting fill.
Also, this was in the 1880-1920 era when filling trestles was most common. People then were not necessarily looking for the perfect solution. The effect of leaving sizable voids is not much different than simply failing to compact the original fill with anything beyond horses or related equipment.
As such, gradual settling will occur. When it does, they just haul more fill to the site and build up the the settled areas. Therefore, many fills are being gradually perfected over time.
The "scoop" Bucky is talking about is the ubitquious "Fresno Scraper" that started in 1883 and were still in use past WW1 until Holt Tractor/CAT really got into the picture. They could be anything from half a pony-keg up to half a 55 gallon drum in size. They contributed much to later bulldozer and motor grader designs plus the horses' hooves added excellent compactive effort.
Railroad standards have evolved over the years as railroads and regular civil engineers began to better understand soil properties and slope stability issues. 1:1 slopes gave way to 2:1 and now 3:1 in places. It all depends on how soils hold together and the mix of fines to everything up to cobbles in the made fill. Gap graded materials tend to fail depending on what you've got.
Jeff: intimately familiar with the BCR&N west of Superior. Kinda sad what happened there. (Uncle Pete demanded a siding on the resulting shortline and would not allow the shortline to interchange at Superior not helping was the fact was UP/CNW did not own the underlying R/W and the people that did were not railroaders - ugly/greedy arrangement that ulimately killed the line.)
I will come back and verify the construction dates and original railroads. Not hard to do if you know what ICC GO-20 is and where to find those submittals. The ROCK lines were all part of the fabled CRIP "bow and arrow country" that were all low density lines that were not high speed and not well taken care of.
UPDATE:
BNSF/MILW = McGregor & Sioux City Ry. (Graded 1878) taken over by Sioux City and Dakota Railway in 1879 and completed.
CRIP (abandoned line) Cedar Rapids, Iowa Falls and Northwestern RR (BCRN of Iowa) 1886......Abandoned 12-29-70 FD-26470...removed by 1973
Murphy Siding, and as that slowly happened, the fill would work it's way into the voids.
After my post, I looked up some info. The BCR&N reached Sioux Falls October 25, 1886. It was under control of the RI at that time.
Speculation at the time was that RI, through BCR&N, was going to build to Bismarck ND and a connection to the NP. This was through the line that ended at Watertown SD. The Sioux Falls branch came off this line at Ellsworth MN. IIRC, a bridge went out in the early 1970s and the branch, now originating out of Estherville IA was cut back to Rock Rapids IA.
The line from Estherville to Superior IA is still operated by UP. The line west of Superior is gone. See this discussion from days of yore. https://cs.trains.com/trn/f/111/t/229115.aspx
Jeff
This is a reply to several posts on this thread.
The line is in Sioux Falls SD next to Southeastern Avenue, north of 41st street. The Milwaukee line is probably graded the same as it was when built. The Rock Island line went out in the 70s. It makes sense that a Milwaukee main line was built to higher standards than a Rock Island branch line. It seems like RI got into the state after the better routes were taken.
My first thought was that the wood underground would rot away slower than wood out in the open, and as that slowly happened, the fill would work it's way into the voids.
BaltACDI would imagine that operating trains continually over the trestle that has been made into a fill would aid in the compaction process as the trestle structure will be subject to vibratory forces with every train the moves across it.
Perhaps those are the same vibratory forces and collateral subsidence that induce "bouncing" track structure?
Perhaps that helps explain why I see the MOW guys so frequently with their little thermite doo-hickey in the vicinity of the yellow arrow? (CWR)
I have to comment though since one of the railroads mentioned has a pretty good reputation in my view. Milwaukee road drained a swamp in Menominee valley in Milwaukee and built a series of drainage / shipping canals as well as a railroad shop complex on it. They also did pretty well traversing more than one swamp West of Milwaukee on the way to the Twin Cities and in Brookfield with the branch to Waukesha. I would venture to guess they were fairly good about building on swamp land.
BaltACD Convicted One Euclid the rotting will cause fill subsidence over time, That was my first thought. I guess my surprise is with the expectation that subsequent remedial action will be "little". I mean if you are talking about a 25' fill, you are gonna have trestle members rotting 25' beneath the surface, And, I'd think that the framing members would really interfere with compaction. Isn't "compaction" the alpha and omega of site prep? I would imagine that operating trains continually over the trestle that has been made into a fill would aid in the compaction process as the trestle structure will be subject to vibratory forces with every train the moves across it. My understanding is that oxygen is required in the decay/rotting process. The deeper timbers get buried in the fill, the less oxygen is available to sustain the process.
Convicted One Euclid the rotting will cause fill subsidence over time, That was my first thought. I guess my surprise is with the expectation that subsequent remedial action will be "little". I mean if you are talking about a 25' fill, you are gonna have trestle members rotting 25' beneath the surface, And, I'd think that the framing members would really interfere with compaction. Isn't "compaction" the alpha and omega of site prep?
Euclid the rotting will cause fill subsidence over time,
That was my first thought. I guess my surprise is with the expectation that subsequent remedial action will be "little". I mean if you are talking about a 25' fill, you are gonna have trestle members rotting 25' beneath the surface,
I would imagine that operating trains continually over the trestle that has been made into a fill would aid in the compaction process as the trestle structure will be subject to vibratory forces with every train the moves across it.
My understanding is that oxygen is required in the decay/rotting process. The deeper timbers get buried in the fill, the less oxygen is available to sustain the process.
Euclidthe rotting will cause fill subsidence over time,
Erik_Mag tree68 One extremely large fill on the MA&N probably still has a trestle under it. The chief reason for building the trestle was to reach a spot on the other side from which fill could be obtained. A perhaps even more important reason was that it was easier to create the fill by dumping carloads of dirt from the trestle, than doing it lift by lift with material carted in. One strong incentive to cover a trestle with fill was to elminate the possiblity of the trestle burning down. FWIW, the Central Pacific had a number of trestles that were filled in after the transcontinental line was finished.
tree68 One extremely large fill on the MA&N probably still has a trestle under it. The chief reason for building the trestle was to reach a spot on the other side from which fill could be obtained.
One extremely large fill on the MA&N probably still has a trestle under it. The chief reason for building the trestle was to reach a spot on the other side from which fill could be obtained.
A perhaps even more important reason was that it was easier to create the fill by dumping carloads of dirt from the trestle, than doing it lift by lift with material carted in. One strong incentive to cover a trestle with fill was to elminate the possiblity of the trestle burning down.
FWIW, the Central Pacific had a number of trestles that were filled in after the transcontinental line was finished.
Convicted One Okay, I'll bite. Why is it that anytime I propose using old railroad ties for landscaping forms, I'm reminded that without proper drainage, they'll rot. Yet here we have load bearing wooden trestles being buried intentionally? What am I missing?
Okay, I'll bite. Why is it that anytime I propose using old railroad ties for landscaping forms, I'm reminded that without proper drainage, they'll rot. Yet here we have load bearing wooden trestles being buried intentionally? What am I missing?
The fill trestle has no purpose once it has been filled, so it is okay if it rots. If the fill is in a previously unfilled area, the trestle is contructed with low quality because it is only needed for the filling work.
However, the rotting will cause fill subsidence over time, which will require subsequent work in the future to raise the track by adding a little more fill.
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