Friday, January 28, 2011

A long experiment

Another thing:

I've been measuring how much capillary rise occurs in several columns of sand. I'll be using the methods and data generated to teach my Soil Science students about the relationship between soil texture and hydrology.

The data above were generated by plastic tubes filled with compacted sand - each tube was a different diameter. I used the same kind of sand for each experiment. And let them run for many days. The first experiment only lasted for about 300 hours, but I let the other two go for over a month. That's more than 1000 hours! Certainly the longest single experiment I've ever done.

You'll notice that one of the tubes shows a marked jump in the capillary rise rate at around 100 hours - I suspect this is due to the presence of more small sand particles (and smaller pore spaces) close to the top of the column. I've split the sand into 2cm "slices" from that column and I will be sieving the sand to check this hypothesis out.

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