Why would you inject tape into the ground?

June 30, 2009 10:12 PM

What in the world is this weird surveying (?) procedure all about?

Images:

1, 2, 3

This was taking place on a small patch of a large lot that's been undeveloped for some time, near Queen and the Don River, in Toronto.

The photos are described in flickr, but basically, a small work crew was using something that looked like a modified pile driver to inject some sort of tape into the ground at closely spaced intervals. It looked like it was going quite deep -- maybe 10 or 15 meters down.

It was hard to tell, but it looked like the tape might have actually been a collapsed tube of some sort.

What the wtf's is the whole thing about?

posted by slipperywhenwet to technology (13 answers total)

I'm going to take a wild guess and say that they're trying to stabilize the soil to prevent slippage i.e. land slides.
posted by Chocolate Pickle at 10:19 PM on June 30, 2009

I don' think there's any significant slope on the site.
posted by slipperywhenwet at 10:38 PM on June 30, 2009

Complete speculation: maybe they're mapping some soil contamination? Pull out the tapes in a couple days and test for pollutants. Sort of like a geotechnical throat swab.
posted by ryanrs at 10:38 PM on June 30, 2009

Re soil testing - I'm not aware of any type of soil testing that uses a ribbon. Soil sampling spots are usually marked off with the little flags, and a sample is taken from the ground - think metal straw witha lid at the end - tagged and then bagged. Most soil sampling are randomized over an area, and then if positive localized. I've not seen this kind of converage before, but I've also never seen an extremely large containmated area either.
posted by bigmusic at 11:26 PM on June 30, 2009

Why don't you go down and ask them?
posted by delmoi at 11:30 PM on June 30, 2009

"Why don't you go down and ask them?"

...'cause, I sort of like the process of trying to figure it out.

Also, I would have had to back track and there was a big construction hoarding between them and I.
posted by slipperywhenwet at 11:33 PM on June 30, 2009

If they are tubes (and it's hard to tell from the pictures but the "tapes" could be a tube with a heat sealed join down the centre) it could be they are planning to freeze the ground [PDF] to assist excavation. Ground freezing is common when digging below the water table or if the ground would otherwise slump into the excavation.

Or it could be soil grouting which is also used to stabilize soils and increase their mass bearing rating.
posted by Mitheral at 11:46 PM on June 30, 2009

Mitheral -- interesting thoughts. I'll have to take a look at both of those more carefully.

I'm initially a little skeptical of the ground freezing -- if they were just doing a perimeter, that might make more sense, but they were infilling the field, and the spacing was pretty dense: around a meter or two, between each ribbon/tape/tube.

I have though about soil stabilization. Need to look into that more. But again, the spacing seems denser than what my understanding of what you would typically do.
posted by slipperywhenwet at 12:11 AM on July 1, 2009

Got an exact location, address, or parcel number? Whatever they're doing will be in the public record and probably online.
posted by ryanrs at 12:42 AM on July 1, 2009

It's not a surveying procedure. It's as Chocolate Pickle says, a ground stabilization method. I am not familiar with that specific method but if I had to hazard a guess it is a first step in injecting a type of subsurface grout. The "tape" you see is probably a flattened hose. The obvious clue is that the soil is extremely sandy. Sandy soil, when excavated can be dangerous especially when all you want is a shaft and not a very wide pit.
posted by JJ86 at 5:30 AM on July 1, 2009

I don' think there's any significant slope on the site.

I think what they're worried about is the weight of the building squeezing the sand off to the sides, and the building foundation settling.
posted by Chocolate Pickle at 11:57 AM on July 1, 2009

Chocolate Pickle said: I think what they're worried about is the weight of the building squeezing the sand off to the sides, and the building foundation settling.

You should have quit while you were aheadd.
posted by JJ86 at 12:41 PM on July 1, 2009

"Soil consolidation using prefabricated vertical drains (also commonly called wick drains or band drains) can reduce settlement times from years to months. Most settlement can occur during construction, thus keeping post-construction settlements to a minimum."

(from http://johngrazelinc.com/foundationsst.htm)
posted by the Real Dan at 6:17 PM on July 1, 2009