You are here


I'm pretty sure I am not going crazy.

The experiments on the 120-140 sand column continue. Calculated viscosities for the 1g/L xanthan are still ~5 times higher than what was found during the capillary tube experiments. We considered the possibility that the new batch of xanthan solution was improperly mixed, yielding a concentration far greater that used in our calculations. This idea, however, was forsaken after we tested the fluid in the capillary tubes again- the viscosities there agreed with previous experiments in the tubes.

After running through my calculations for the 4th, 5th, oh-I-lost count, times, I decided to flush the column with water and verify the value computed for the sand's permeability. Now comes the interesting part (if you could call it that); the hydraulic gradient I measured during this second go-around was much higher. What is happening?? Oh, I remember now..

During our experiments we had noticed the sand in the column was settling out. Some of the finer material, I suspect, was able to pass through the screen on either end. We decided to repack the column so that the assumptions used in Darcy's Law were still valid (the fluid needs to be passing through a porous media, not a pipe). The experiments were continued without confirming the hydraulic conductivity. In a sense, the sand did have a time-variable permeability.

I was on my way to establishing the new value of the sands permeability when it happened. The fluid reservoir ran dry and the pump began pushing air through the column. Once air is in the voids, it is nearly impossible to displace it with water and the column is useless. The Labview vi takes about 15 seconds to turn of the pump. All I could do was watch while the life was sucked dry from my first soil column.

Yesterday I made a new column (Dr. Johnson makes it look way easier than it actually is). It will never compare to the one that was thrown away, but life must go on. I am back where I started and hopefully this time things will go much smoother.

Thanks for reading.