Building safe, adequate, durable roads over permafrost soil presents unique challenges to the construction industry. It is not suprising that the mechanisms that lie behind these challenges are explained by the laws of physics. Consequently, as concerned professionals from the engineering community look for inovative ways to deal with the permafrost specter, it is in the realm of physics where they look for the elusive techniques that will enable the extension of the transportation infastructure into the northcountry in a safe, efficient, wise, and economic way.
This paper will explore the techniques used to build road embankments over frozen soil. In exploring these techniques, every effort will be made to demonstrate the physical concept that is pertinent.
But prior to our examination of diferent methods of permafrost resistent roadbuilding techniques we must start by going back to basics. To understand the construction methodology of arctic roadbuilding we need to understand the mechanics and properties of permafrost.
It's All About Heat
* What is Permafrost? Permafrost is defined as ground that has been at a temperature below the freezing point of water for more than two years. A large portion of the ground in Alaska is defined as permafrost (some estimates say as much as 80 percent). Permafrost can extend to a depth of several hundred feet, or it can be as little as several feet deep.
* Is there permafrost in Fairbanks? Yes. We live in an area defined by "discontinuous" permafrost. This classification refers to the fact that some of the ground is frozen, and some of it is not. Also, it is important to note that the permafrost in this area is known as "warm" permafrost. Warm permafrost is at a temperature of approximately 31.5 degrees F .In other words, if it got just a little tiny bit warmer, it would melt (and by definition, it would no longer be permafrost.)
* So what's the big deal if it melts? Well, possibly nothing. By definition, bedrock that is beneath the freezing point is considered to be permafrost. If this were to thaw, there would be no catastrophic results for the structures that sit on top of it(frozen gravel deposits also remain relatively stable after thawing). When assesing the fragility of permafrost, we must consider the soil type. Much of the perrenialy frozen ground in our region is composed of a silt type material with an extremely high moisture content (30-50 %). In fact, there is so much moisture that there are actualy large hunks of pure ice enveloped by the soil. When ground of this composition thaws, it loses it's strength. Any roads or structures that may sit on the surface are subject to sink, often with devastating results.
Let's say you were going to build a road. You probably wouldn't build it through the middle of a swamp. A swamp is a wet, mushy, unstable quagmere of mud. A road built in these conditions would be sure to fall apart and crumble into ruins in quick time. It...