Ch. 14] APPLICATION AND SOLUTION OF THE PROBLEMS 261 



Black-top pavements are good conductors and heat absorbers in sum- 

 mer and can destroy permafrost. An elevated and insulated building 

 with circulating air beneath can be more than enough to unbalance the 

 thermal regime of the ground toward permafrost. Under fixed labora- 

 tory conditions heat conductivities of some earth materials are known, 

 but the quantitative effect in nature of variable moisture conditions 

 and of changing vegetation is not. Changes in the volume, composi- 

 tion, or temperature of ground water or surface runoff have effects as 

 yet little known qualitatively or quantitatively. 



All these factors must be considered to be in a delicate balance be- 

 tween freezing and thawing. It is to be emphasized that the thermal 

 regime is not uniform, but changing from hour to hour, day to day, 

 week to week, year to year, and cycle to cycle. Specifically we must 

 think in terms of geographic position, topography, lithology, structure, 

 and texture of soils and bedrock, hydrology, geothermal gradients, 

 thermal conductivities, vegetation, climate (temperature, precipita- 

 tion, cloudiness, wind, insolation, evaporation), and cultural features. 



What effect cosmic dust clouds, changes in carbon dioxide con- 

 tent of the atmosphere, inclination of the earth's axis, eccentricity of 

 the earth's orbit, sun spots, etc., have on permafrost can only be sur- 

 mised as they affect insolation and dissipation of the earth's heat. 



PRACTICAL APPLICATION AND SOLUTION OF THE PROBLEMS 



In a permafrost area, it is imperative that the engineer have a com- 

 plete understanding of the extent, thickness, temperature, and character 

 of the permafrost and its relation to its environment before con- 

 struction of any buildings, towers, roads, bridges, runways, railroads, 

 dams, reservoirs, telephone lines, utilidors, drainage ditches and pipes, 

 facilities for sewage disposal, establishments for ground-water supply, 

 excavations, foundation piles, or other structures. The practical im- 

 portance of the temperatures of permafrost cannot be overemphasized. 

 A knowledge of whether permafrost is actively building up, is stabil- 

 ized, or is being destroyed is essential in any engineering problem. Past 

 experience has amply demonstrated that low cost or high cost, success 

 or failure, is commonly based on a complete understanding of the prob- 

 lems to be encountered. Once the conditions are evaluated, proper 

 precautions can be taken with some assurance of success. 



Muller (1945) gives comprehensive outlines of general and detailed 

 permafrost surveys as adapted to various engineering projects. These 

 outlines include instructions for the planning of the surveys, method of 

 operation, and data to be collected. Rarely does the geologist or 



