Earthwork is the foundation which roads, whether highways or railways, are built on.

22 Replies to “Weekend open thread: Earthwork”

  1. And here’s a bet for somebody of a “sportin'” bent: is the wheel a universal mechanism the equivalent of a planet, or only a back-stop ’til gravitation itself runs its way through it’s every possible chance push-pull permutation?

    Which (sits up and begs) this week’s conundrum. If we only dig in the right place, with our tool at the correct angle, can we ever create a transit system that will either roll forever or hold itself in place without a unit of investment in any currency in the Universe?

    Or is this entire concept a matter if ascertaining whose mistake screwed up everything worst. Last. Meantime, my best take is if it’s got your approval, Oran, it won’t kill passenger one no matter how hard they try to commit suicide. Even if they dig themselves in every time they lie down.

    Mark Dublin

  2. It’s a good basic summary about any surface construction! It’s applicable to all modes from trails to rail tracks. Of course, the heavier the pounds per square inch, the stronger the earth must be. It’s one reason why light rail is more involved than building a street is.

    1. Ah, nice try, but no.

      A fully loaded LRV and a fully loaded tractor trailer rig just aren’t that different in weight (LRV slightly heavier), but an LRV spreads the load out over more load bearing axles. Additionally, the steel rail an LRV operates on is stiff and spreads the weight out over a larger physical area, resulting in lower local loads.

      And think of a loaded freight car! With weights at 2 to 3 times the weight of an LRV it typically has only 4 axles and operates on a little pad of soil which is typically raised above local ground level. No problem.

      So ya, there are difference, but soil compaction requirements aren’t one of them.

      1. LRV spreads the load out over more load bearing axles.

        How do you figure. An 18 wheeler has 18 contact points all much larger than the virtual single point contact of a steel wheel LRV. If a truck rolls over your toes you might be OK. If a LRV does it they are amputated. With rail all the load is taken by the ties. The gap between the ties doesn’t support the rail. The crushed rock (ballast) thickness is much greater for rail vs roads.

      2. An 18 wheeler has 4 primary load bearing axles (the front axle supports mainly just the cab), an ST LRV spreads the load out across 6 axles.

        The wheel to rail contact area is only about the size of a dime for each wheel. It is the rail itself that spreads the load out over a wider area extending out from each axle.

        The purpose of ballast is to lock the track in position laterally and longitudinally, provide drainage and to control vegetation growth. It is fundamentally why ballast is always angular rock and never smooth stones. And it is why ballast is cleaned periodically.

      3. My first guess would be that, in the US, road construction companies are a dime a dozen, whereas for rail construction companies, you might be limited to a choice of one or two. So, simply having a project be rail might make for a fatter bid with a heftier profit margin. Similar with ordering the vehicles, as there’s a lot more companies out there that make buses than make railcars.

        Not to say rail is inherently bad – if enough cities do it, maybe we can get the economies of scale here that they get in Europe or Asia. It’s just one more piece of the cost that has to be taken into account.

      4. Thanks Bernie. Clearly rail has to have more substantial earthwork. I’ve witnessed lots of rail and road construction as they have been built, and the rock depth under ties is always substantially deeper under road pavement. Rail also requires a longer braking distance because the contact surface is less, and the Lake Washington bridge had to be significantly modified for Link.

      5. Lazarus, the ballast also spreads the load. And that is why it is broken rock. The individual stones lock themselves together and transfer the weight from the ties over the entire width and depth of the ballast. .

      6. @TomT,

        Not exactly. Vertical load bearing is just one of of the roles the ballast plays, and the weight of the vehicle is not spread out over the entire width and breadth of the ballast as you assert. In fact, the amount of ballast that supports the vehicle weight under a given tie is relatively small.

        Ballast resists track motion in all directions, which is why railroad ties are placed IN ballast and not just ON ballast. You will never see track just sitting on top of ballast, because such track would be unstable. And this is why the ballast extends well beyond the ends of the ties onto the shoulders.

        But hey, the age of “alternative facts” still persists. But go take a look at a railroad sometime. Or use the Google.

        A note of warning though: trains operating on modern continuous rail are incredibly quiet, and being in the railroad ROW is trespassing and you will be subject to fines or arrest. Don’t do it unless you are authorized.

    2. Stand (at a safe distance) next to ballasted railroad tracks as a coal train rolls by. Watch the tracks flex up and down.

      It’s all about how the load gets distributed.

  3. Well done presentation. One thing I’d add is that geofoam is now replacing a lot of earthwork. The SR-167 to I-405 connector is an example. The large fly over ramps are primarily supported by foam blocks instead of compacted fill. This saves a lot of time and lowers the carbon footprint associated with moving and compacting. We’ll see how this holds up over time. One concern I have is what happens to the foam if there is a very hot fire like from a fuel oil truck. These have compromised the integrity of steel reinforcement in bridges.

    Rail, from what I’ve been exposed to is different in that the ballast is integral to the drainage. That differs from roads where all the drainage is surface runoff handled primarily by storm drains. Said surface water needs to have oil and other contaminants separated. For the most part, the water along rail lines is pretty clean.

    1. “The carbon footprint associated with moving and compacting”

      Has anybody put any thought into electrifying construction equipment? You would think that if a semi truck can run on electricity, then so can a bulldozer.

  4. The video gave a ball park $3M/mi for a two lane road. Of course that’s going to be much more expensive in an urban area where you’re looking at extensive demolition and utility relocates. What is the ball park figure for one mile of light rail and what has ST averaged per mile?

    1. In completely rural and flat areas a mile of railroad track will cost between one half and one third of what a lane mile of paved road will cost. This is primarily due to the simpler construction of rail.

      In urban and hilly areas all bets are off. Additionally, a lot of the cost of transit systems like Link are in the systems themselves and not in the basic construction of the track. It is fundamentally why heavy construction for Link occurs so fast, but then things appear to move really slowly. Systems are hard. They take time and they need a lot of testing.

      And stations can be very expensive.

  5. For what it’s worth, but based on experience putting me in a position to know whereof I speak, in addition to being President of the United States, Joe Biden’s experience and inclinations solidly mandate that from this point forward, the President of the United States shall stand both ready and completely permitted to take the steering wheel or the train-controller of anything wheeled which Fortune and the history of his country shall place at his convenience. Really spoiled pet dogs count too!

    Word to the Secret Service. By all the earmarks of the trade, this President will never misinform a passenger regardless of age or attitude, or by any change of speed or misreading of pavement angle, even come near causing the most shamefully over-obeyed animal to even grumble, let alone growl.

    Joe Biden’s present job title? History’s call. But his handling-to-come from the approaching Rush Hour Out Of Hell…..Best have Intel’s best observation + imagination At The Ready.

    Word to The Secret Service. Better get somebody who knows how to sing in uniform to prevent disaster, because my old Gibson six-string flat-top’s always at the ready. It’s your National Anthem, Mr. Defense Secretary, to commemorate at rush hour’s upcoming worst! My duty as a citizen? Thankfully, done and then some.

    Mark Dublin

  6. Why can’t the next West Seattle Bridge be cool looking? Look up the Vincent Thomas Bridge in San Pedro, CA. (Btw, it’s the bridge the director of Top Gun committed suicide off of, and it’s the bridge that Agent Richard Chance bungee jumped off of in the movie To Live and Die in L.A.). That bridge has character!

  7. Cool looking bridge. Not sure what it would cost to build. Would such a bridge be able to handle light rail, if light rail is affordable for West Seattle? If light rail isn’t part of a new bridge (including second transit tunnel so their ride isn’t a “stub”), I imagine residents of West Seattle will demand no loss of car capacity in any new bridge, including dedicated bus lanes, which is 6 lanes minimum, although that is decades in the future.

    Interesting article in today’s Seattle Times. Right after the closure of the West Seattle Bridge rents and sale of houses declined, and residents were quite worried. However, after the announcement the bridge would be repaired and not replaced rents and sales rebounded, and West Seattle had a smaller decline in rental rates in 2020 than Capitol Hill and Bellevue, which surprised me.

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