How do you dig out a slope while controlling the spill?

November 29, 2017 12:44 PM

If I have to dig out after, say, a landslide or a rockslide along a tall vertical surface, what's the way to do it while controlling spill? Is there a proper technique for this? Does one start at the top and go along in sections? The pile of dirt and rubble in question would be about twenty or thirty feet high.

This is fiction, so I'm not worried about contractor licenses or whatnot. Machines like backhoes are available, but I'm sure there are methods to that. I'm wondering how to describe the technique. The pile is up against a relatively sheer rock surface, so there's a definite end to it on the backside and the goal is to clear it out to that rock. I keep wondering if one goes in sections, creates terraces, or if I'm overthinking and it's a matter of "just dig."

I'm not coming up with much on Google, probably because I'm not sure what search terms to put in.

posted by scaryblackdeath to Grab Bag (6 answers total)

You could have a look at the techniques used since the November 2016 earthquake near Kaikoura, New Zealand. Immense rockslides are still blocking the main north-south highway even today. After engineers crawled all over the site, the first stage was abseilers detonating loose rock above the cliffs, and then helicopters with monsoon buckets washing the loose stuff down the cliffs. There's no point starting to dig until the site is safe from further falls.

After that, the diggers tended to work up digging themselves a route to the top of the spill and working down from there. The very last thing you want to do is "just dig", as you can't predict exactly where and when additional slips from the unstable pile are going to happen, and that's not a viable way to run a work crew.
posted by tillsbury at 12:53 PM on November 29, 2017 [2 favorites]

Yeah remove in a series of benches and terraces, with the equipment moving down benches. Shore up the lower benches until removal. Soil/rock has a natural angle of repose so just digging works against yourself. Look up excavation techniques?
posted by cakebatter at 1:58 PM on November 29, 2017 [1 favorite]

I would think this also depends on whether you are attempting a rescue or just road clearing.
posted by Gneisskate at 2:34 PM on November 29, 2017

Best answer: Angle of repose is the key concept. Generally, safety and reliability will trump speed of digging, unless maybe it's just one person digging and they think their spouse is in there alive, or other contrived examples.

That is, professional rescue crews would/should be mitigating the worst case (additional loss of life), rather that optimizing fastest clearing (if all goes well and you're lucky), but the calculus may change according to who may be in there, who the diggers are, and how big the pile is.

For fiction, I'd say just paraphrase key bits from the answers above and fall back on "angle of repose" as explaining why your characters do whatever it is you want them to do in terms of cautious/slow techniques.
posted by SaltySalticid at 5:07 PM on November 29, 2017 [1 favorite]

Machines like backhoes are available

Others have mentioned the right way to do the excavation (from above, and with consideration of safety from additional slides). I would add that the excavation process needs to consider the hauling of material, preferably in a way that the dump trucks or off road haul trucks can run in a loop (rather than having to back up to get loaded), and that if the quantities are at all significant you will be using track-hoes (aka excavators), not backhoes.

How far the material needs to get hauled (as well as how large the pieces are, how wet it is, etc) will determine how long it takes to haul it all away.
posted by Dip Flash at 3:54 AM on November 30, 2017 [1 favorite]

If it helps for you to see it in action, many state departments of transportation provide videos of landslide repairs (examples: Oregon DOT, Arizona DOT), which show the kinds of machines involved, the steps in the process, and how complex the engineering solutions can sometimes be to prevent the problem from reoccurring.
posted by Dip Flash at 4:07 PM on November 30, 2017 [1 favorite]