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?
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
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.
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.
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.
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.
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.
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...
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!
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.
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.
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?
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.
Euclid I assume that this visible part of the trestle has never been filled
In this case it was completely filled, and ballasted. Variously shored up with concrete retaining walls in some areas, oblong blocks in others, as well as just sloped fill with grass planted on it in yet others.
Obviously we've got a "57 varieties" collection of opinion, as to what is proper. So much for consistency.
Convicted One Euclid I assume that this visible part of the trestle has never been filled In this case it was completely filled, and ballasted. Variously shored up with concrete retaining walls in some areas, oblong blocks in others, as well as just sloped fill with grass planted on it in yet others. Obviously we've got a "57 varieties" collection of opinion, as to what is proper. So much for consistency.
diningcar 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. I'll have to give you your props for being 90, or 91? Using a PC. You're a rare breed, and to the others on here with many years behind them. I can't even count on my hands the number of boomers who came after you. That refused to adapt and use computers..
I've adapted to the computer since it has helped my accuracy at work. My prior experience of having to do many of the same calculations manually in the past is an asset since I often have a good idea of what should be coming out of the computer. The problem lies with the younger employees who never seem to grasp GIGO (garbage in, garbage out) and assume that the output will always be correct.
EuclidI had assumed that the image you showed was the completed project. Apparently that is not the case. So, is this an illustration that you have composed showing the work in progress before it was finished? From your last comment above, I assume that the image does not show the finished work, since you say the entire space below the top of the timbers was filled.
I'm sorry that I was not more clear about that. My sketch was just intended to show the basic style of the trestle in the "work in progress" photo that I found. Since I do not own the rights to the photo, can't post it here, so I drew the sketch.
In the actual photo, the work progresses over approx 100 running feet with a dirt fill operation followed by a ballasting operation. And that was just more detail than I felt like drawing... Perhaps a total of 5 linear miles of grade separation raised in this way
When the dirt fill was in progress, it appears that they stacked oblong blocks, similar in appearence to parking lot bumpers, along the edges of the trestle to shape the fill against. Since covered or replaced with poured cement in most areas.
Thing about the actual photo, for years I had assumed that the "trestle" shown in the picture was just temporary false work. And not until this thread did I really notice that they were pouring the dirt right in around the wood.
I'm not a civil engineer, so fact-check anything I say.
There seems to be an idea in some posters' minds that wood surrounded by fill will rot and disappear in a few years, just as it would if exposed on the surface, and consequently there would be piling-sized voids into which the fill would collapse. I'd suggest that considerable mass would remain, and that it would have some compressive strength against the fill even if it ceased bearing the load of the track.
A very common approach I see to 'new' fills in general construction is to build them up substantially above finish grade, then leave enough time for natural compaction to develop. Interestingly, although I have seen use of sheepsfoot rollers (like those on excavators in landfills) in road subgrade compaction, I have not seen them used on top of these oversized fills, which may add some emphasis to Euclid's opinion about overcompaction of the upper part of a fill.
OvermodThere seems to be an idea in some posters' minds that wood surrounded by fill will rot and disappear in a few years, just as it would if exposed on the surface, and consequently there would be piling-sized voids into which the fill would collapse.
Personally, I suspect the rot would be random, uneven, and nonpredictable.
And, much like Neil Young's rust...eternal.
I'll tell ya what I've REALLY taken away from this conversation. When I originally put in those raised flowerbeds using stairstepped surplus crossties, and all my "well meaning" critics pointed out that the ties were sure to rot, I should have just countered with "and by that time my son will be big enough to replace them"...and just left it at that.
Building structures and fills on reed or wooden mats was common in the 18 and early 1900's. It would remain stable as long as you kept the mats from being exposed to air or fresh running water (air entrainment)... There are major bridges and piers/bents in multiple places crossing rivers that are still very structurally sound.
As soil mechanics and loads changed, the method has gone away.
It was also common in large civil projects to build temporary track or build temporary very narrow gauge railroad to move fill material and stone on worksites. Very rickety, but still got the job done.
One thing I don't think I've seen mentioned is that the weight of fill will compact the fill below it depending on the density of the fill material.
MidlandMike One thing I don't think I've seen mentioned is that the weight of fill will compact the fill below it depending on the density of the fill material.
The generation of field engineers and soils engineers prior to Peltier and I in Diningcar's early years did yeoman work in re-writing our understanding of soils under railroad loading.
Of course when the fill is pressing down on itself it helps if there is a solid base pushing back up. Also its not helpful when the fill is waterlogged making the vertical component of force go horizontal.
With respect to filling in wood trestles, the following data on shrinkage in fills was taken from the 1924 Edition of the Electric Railway Handbook. The two scenarios are "raising under traffic" and "trestle filling".
Soil type Raising Trestle
Black dirt 5% 15%Clay 5% 10%Sand 5% 6%
With respect to wood rotting when buried in soil - I've seen telephone poles stand for decodes, albeit they are treated with creosote. The same handbook mention above stated that placing concrete against a wood pole at the ground line does measurably extend the life of the pole. Note that this was when untreated wood was still commonly used for electric railway work.
Wood - particularly if it's been creosoted - that's completely buried in the ground is going to be around for a long, long time...like hundreds of years long. It's wood exposed to the elements that's going to rot. That's why you paint your house, to protect it from sun, rain, heat, cold, wind. A lot of what destroys exposed wood is temperature shifts - water seeps into the wood from rain then freezes when it gets cold, cracking the wood and allowing more moisture and air inside. Wood that's underground is in an environment with a very stable temperature and humidity, and little access to air. It can almost be like it's sealed in.
Murphy SidingI find this a little bit troubling, as I'd always heard that the Rock Island line was a mighty good road.
That line from the old song has more to do with the Rock Island being one of the few railroads that would hire railroaders fired from other railroads for participating in the Pullman Strike of 1894. It wasn't an accurate reporting of the quality of the railroad, which was often struggling financially due to it's tendency to be the last railroad to reach a city, usually by the most roundabout route possible.
Murphy SidingFor example, in a half mile stretch the Rock Island ROW rises and then drops 12 feet.
The fact that those dips are there now in the bike path doesn't necessarily mean they were there when it was a railroad line.
wjstix... Murphy Siding For example, in a half mile stretch the Rock Island ROW rises and then drops 12 feet. The fact that those dips are there now in the bike path doesn't necessarily mean they were there when it was a railroad line.
Murphy Siding For example, in a half mile stretch the Rock Island ROW rises and then drops 12 feet.
Carriers, without a proper financial footing and capitalization, tended to build their tracks on the lay of the land, rolling through hills and valleys. It costs money to do grading and put trackage on a steady footing - making a cut through a hillock and filling the dale.
Growing up around the B&O, I notice early on that trackage was construted on a steady line. When I got down to Jacksonville and viewed how the CSX tracks around the city took the lay of the land over hill and dale. Such construction was indicative of Southern railroading eminating from the Civil War era where the North was a industrial area that was investing heavily into railroads and manufacturing. The South by contrast was agrarian in nature and was continually searching for someone to invest in their plantations and railroads.
wjstix Murphy Siding For example, in a half mile stretch the Rock Island ROW rises and then drops 12 feet. The fact that those dips are there now in the bike path doesn't necessarily mean they were there when it was a railroad line.
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