The Ground was Melting

The top of the world has many interesting features; high amounts of UV, lots and lots of snow, fierce wind storms and the interesting phenomenon that during the extremely short summer; the ground melts. Yes you heard me right. The ground melts. Try to build a building on soil that melts. We had to. And to make it even tougher, we had a critical deadline.

The deadline was selected so we could finish before the peak of the very short summer that occurs at the North Pole. Thing was, however, nothing went right that year and we began to fall way behind in getting our work done. To finish and be able to deal with the melting soil, also known as Permafrost we had to come up with some very innovative ideas.

In short Permafrost is a combination of soil, water, sand and crushed rock. It exists as natural soil in the Arctic area and is usually soil that has been frozen in this state for at least two years. You can build on it as long as you don't leave it exposed above 30 degrees F and exposed to the sun, for long periods of time. If you do this, it turns to mush and runs like mud. That is exactly what was happening because we fell behind in driving the piles for the buildings' foundations.

The air temperature was now in the 30's and the Permafrost was exposed to the sun. In order to drive the piles and keep the ground frozen we devised a method of freezing the ground with liquid Nitrogen. First, we mapped out the areas where we had to drive the piles. We then ran a series of calculations to see how much Nitrogen would be needed at each different site where a pile had to be driven. We had calculated that to get the heat transfer we needed we had to drive four 3 inch pipes around the spot where we were going to drive the piles. We then calculated the amount of Nitrogen we needed and added a 30% safety factor and pumped away. The pictures above indicate what the spots looked like where we had to refreeze the Permafrost with Nitrogen.

Though our calculations were fairly accurate we still had to experiment with the actual location and depth of the Nitrogen pipes. The calculations however gave us a good starting point. To perform the calculations we assumed that the Permafrost was a homogeneous material. This of course was not the case and introduced an error which we had to correct for in the actual placement of the Nitrogen pipes and the amount of Nitrogen required to freeze the earth.

The first parameters we tried caused the Nitrogen to escape much to fast without really freezing the amount of ground that it had to. We tried many different methods of injecting the Nitrogen so we could get just the right amount of Nitrogen liquid to enter at the right rate and to stay in the pipes long enough so as to freeze the right amount of permafrost. The depth of the pipes also had to be played with. First we tried 2 feet, no good...then we kept increasing the depth by 2 feet until we had all the parameters just right. It took forever to do this. By the time we got it just right, the Permafrost melted so much that it actually started to run down hill no matter how level the slope was. Just the slightest unevenness and the Permafrost started to flow.

It took several days to get it just right but because the makeup of the Permafrost varied from location to location we had to keep repeating the process to tweak it for each different pile location. It took at least 10 hours to do just one pile location. The Nitrogen pipes would get so cold that they would crack. The soil conditions were so different from location to location that it sometimes took us hours to get the right combination of parameters so the ground would freeze before the pipes would crack.

It was a long cold summer north of the Arctic Circle, and we used an endless supply of pipes and tons of Nitrogen. Working 24/7 we were able to keep the ground frozen until nature took its course.

Hal