Comment by chrissnell | Hacker News Reader

Comment by chrissnell | Hacker News Reader

I would love to see that first bulldozer at work. I'm a little amazed because snow becomes incredibly heavy and hard to move/push when it's packed. As the blade moves forward, that dozer will quickly have to use incredible force to move forward.

I experienced this first-hand last summer when I was driving my old Land Rover across the country. I was solo, way up in the very remote Henry Mountains [1] of Utah, about to reach the crest and continue east. I came around the bend and there was a massive drift of snow covering the trail. [2] Foolishly, I thought I might be able to drive through, or at least ram-reverse-ram-reverse-ram my way through. I should have known better. I drove into the drift and my tires sank and the face of my front axle compacted the snow ahead and just stopped. The entire front of the truck was encased. It had been a warm day and was rapidly chilling in the evening light and the wet snow froze around my axle and my truck wouldn't move an inch. I spent the next hour digging out the front of the truck in fading light and by some magic, was able to free myself and back down the precarious cliffside road to a spot where I could turn around. Lesson learned: snow is really heavy.

[1] https://goo.gl/maps/XjyNapW3XRL2

[2] https://www.flickr.com/photos/defender90/27742972523/in/albu...

The article goes on about it. They send a remotely operated dozer with GPS to blaze a guide path, then other dozers come in to take off layers and then it's down to 6 or so feet they send in the blowers. So, it's many machines doing many passes to get the job done.

I do appreciate the pristine snow not contaminated with rock salt, however.

It's not remotely operated:

> The GPS and sat phone work in tandem to provide the driver a detailed video screen image of the dozer’s location in relation to the center of the snow-buried highway. This driver’s job is not to clear snow, but simply to lay out an accurate track of the road itself.

Reading it again, I think you're right

Makes me think though why could they not manoeuver it remotely with remote feedback if necessary, why put someone in the cab if they have it equipped with sensors. Some other heavy equip are operated remotely.

In fact, in a lot of situations, Humans are just cheaper.

because if the terrain is dangerous to drive on (with all that snow, probably yes), the driver will likely judge much better than anything you could do remotely with current technology on whether to risk moving ahead or not

possibly, sensors have difficulty with snow? Low coefficient of friction, high reflectivity, differing levels of compressibility, difficult to judge slipping tracks, etc. Dead reckoning based on the track output probably doesn't work great.

One of the reasons to put tracks on a vehicle is to reduce the pressure it exerts on the ground. A bulldozer might weigh 15x as much as light truck, but if it has 75x the contact area, it would have (much!) lower ground pressure, and would be dramatically less prone to sinking into snow or mud or what-have-you.

Some sanity checks:

1993 Toyota 4Runner / Hilux Surf: 25 psi (https://en.wikipedia.org/wiki/Ground_pressure)

Caterpillar D6R LGP Bulldozer: 5 psi (http://www.ritchiespecs.com/specification?type=Con&category=...)

Some tracked vehicles like bulldozers are available in extra-wide track versions to reduce their ground pressure even further. It wouldn't be surprising if most of the snow fleet is so equipped.

5 psi doesn't seem like much at all! I wonder if that's a pressure survivable by a human.

Likely depends on how many square inches of the human are covered, and where on the human they are located.

For arguments' sake, the whole human.

This kills the human (joking... I don't really know)

Let's say an human with height 170cm and hip width of 85cm (these are between the averages men & women) gives a rectangular area of about 1.4 m^2; the head and legs aren't as wide as the hips, but this doesn't include the arms, so let's take it as a guess of the weight-bearing area for a prone or supine human. This area times 5 psi is more than 5,000 kg (more than 11,000 lbs). So yes, I think it would kill someone.

Surely not? The point of pressure is that it's constant per area, so no matter how much is covered, the pressure felt is still 5 psi.

No. Put 5psi on a 1 inch x 1 inch area of my hand and I will be okay.

Put 5psi on a 12 inch x 24 inch area of my torso, and I will be very much not okay.

this is correct

Torque. It must be a low-range, diesel beast. It probably can't go that fast, but it's probably harder to stop than a single locomotive.

Young me does want.

Keep in mind that bulldozers routinely shove other, equally dense, materials around.

To be fair, much denser materials. A cubic meter of ice (which is clearly heavier than snow) weights 1,000 Kg, any terrain/gravel/sand will weight between 1,600 and 2,000 Kg per cubic meter.

Sounds like you bottomed out. At that point ordinary vehicles no longer get traction from the wheels because they don't have enough weight on them, in addition to the fact that being caught in the snow means you need more traction to move.

Treaded vehicles don't have this problem if the snow is reasonably compact or they have wide enough tracks to avoid sinking in, as do snowcats or snowmobiles.

No, in my case, the axle, steering, and bumper sank into the snow and were encased. The motor simply did not have enough torque to turn the wheels. To get out, I had to excavate the entire front of the truck and then dig out a path for the front wheels to roll backwards.

Remember also that there's a big difference between the fluffy powder they're plowing in northern Japan and the wet stuff you drove your landie into.

The top may be fluffy, but by the time you've dug through the top 50ft I doubt it's very fluffy anymore.

It's dense fluff...

There is a very wide range of snow. In particular, the heavy wet stuff acts and behaves very differently from "dry" snow -- whether that's light powder on top, or compacted, but dry, snow underneath.

Wet snow is increadibly heavy, and frequently contains or mixes with ice which makes removal (blowing, ploughing, shoveling, 'dozing) far more challenging.

Compared to rocks, ice is not that dense. You can try yourself: it's easy to pickup a big chunk of ice, even with a shovel, while a similarly sized rock is impossible to lift.

And ice, quite surprisingly, is less dense than water. There are not many solids that are less dense than their liquid form.

Exactly one: water/ice

"Other substances that expand on freezing are acetic acid, silicon, gallium,[35] germanium, bismuth, plutonium and also chemical compounds that form spacious crystal lattices with tetrahedral coordination."[0]

[0] - https://en.wikipedia.org/wiki/Properties_of_water#Density_of...

There's more than water. A lot of things that freeze into a crystal lattice can be less dense than their liquid states. Silicon dioxide is another IIRC.

...And some places have "lighter" snow than others.

I have seen experiments, where you fill a large glass with snow from the alps - and another with snow from the Rockies (US/Canada). When melted, there is only half the water in the glass from the Rockies - which is why it is powder-heaven for snow-freaks (such as myself).

I have no idea about the science - why it is this way.

Try that same experiment with a snow bank in late May from both places and you'll likely find it's equally compact once the snow pack is at 32F throughout and starting to form what is known in the trade as firn. [1]

[1] https://en.wikipedia.org/wiki/Firn

Your linked photo hardly looks like a road.

It's more of a trail. It's the northern pass over the Henrys, a BLM road. I got stuck right about here:

https://goo.gl/maps/ZcNVUUhgJQ12

My first intuition was to drop a street view person on the map there. In retrospect, this was silly.

In glacier national park they use excavators for the first passes.

That's for Going to the Sun road. They don't usually punch a hole through it until May or June, either.

Presumably they don't let a 40 feet of snow or whatnot accumulate at once. If they just clear 1-2 feet of snow every night all that involves is having a plow that can throw up the snow high enough to the sides and out of the way, which seems plausible. I say this because I presume clearing 40 feet of snow is rather impossible.

I think they were referring to a road that is not plowed all winter and in the spring they send in the bulldozer to clear an initial path until a snowblower can handle it.

>The first bulldozers will push and carry the snow forward, to areas where depths are lower and it can be pushed aside or dumped. Backhoes are used to help widen the road. When the bulldozers have come within six feet or less of the road, the rotary blowers can begin their work, and help to at last reveal the long buried asphalt.

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