Saturday, April 14, 2012

Urban soil analysis

Under the pavement: the beach?
A famous Situationist International slogan by Guy Debord, also translated as: "Under the paving stones, the beach". But has anyone really tried to test this hypothesis? In reality the urban soil under the pavement is  more complex than that. And fortunately the ever present roadworks enable us to study urban soil in detail.
Urban soil layers
At the moment the quay of the 4e Westwagenhof is being restored. The soil has been dug up to a depth of only 1 meter. This no archaeological level, it cannot be older than a few years. But already interesting soil patterns can be observed.

There are 4 layers here, or more. But I'm sure about these ones:
  • the paving stones (200*100 mm) - useful for scale
  • dry sand - it probably dried during the roadworks
  • wet sand - it also could have a relationship with the ground water level
  • dark clay - might be more than one layer
The transition between dry and wet sand.  The transition between the sand and the clay. 

Methodical errors
I'm learning the craft on-the-fly, without any theoretical preparation. So I make all the stupid mistakes. For example ... I only took a soil sample from the heap of sand that had been dug out of the hole. And I took only the sand. In hindsight the clay layer would have been much more interesting because it is older.
Where I took the sample. Not good.

Another error I made is not labeling the container with the sample. I almost forgot where it came from and had almost thrown it away as worthless.

Soil analysis attempt
Weight = 47 grams (using my digital kitchen scales)
Volume = 33 cubic centimeters (estimated by measuring the height in the container)
Density = 1.4 grams / cubic cm
The density of dry sand = 1400 - 1600 kg / cubic m - so this fits the range perfectly.
There is no smell. The sand contains a lot of tiny fragments of cement and asphalt. The sand grains are small and the sand feels very smooth to the touch. But still there are a lot of different grain sizes; the sand looks very unsorted. And there are no seashell fragments. Most likely this is not a beach! I could test this by tasting for salt, but I don't think it would be wise.

I thought I had a spare tea-sieve, but right now I can't find it.

There are a few "concretions" clumps of sand in a cement-like matrix. The chalk might come from the mortar in the canal walls. Or maybe the sand has been used before on some building site.

Scientifically the experiment is worthless. But poetically it makes you aware of the urban underground and it's unfathomable history. It also highlights the variety of underground soil mixtures, colors and textures. To be continued.

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