In the early days of Fairbanks, before the hazard of permafrost was fully understood subsurface explorations were not common and as a result many buildings were unwarily constructed on permafrost. In some cases, it didn't take very long for the presence of permafrost to be discovered. In some cases, builders actually had full knowledge of permafrost but overestimated the ability of buried insulation to prevent thaw. In some locations, the resulting distress varied and evidence of this can be seen on Army Road and Madcap Lane off of Farmers Loop Road, not far from UAF. Some of the distressed buildings in this area are now home to UAF students and others and, while in various states of minor distress, the structures continue to safely shelter a family. Some distressed buildings off of Farmers Loop Road became uninhabitable and were ultimately demolished.
As experience and knowledge of permafrost grew, testing became more commonplace, problems were reduced, and a knowledge-base was gained. Areas that were generally permafrost-free were eventually identified and have since been developed. As development continues, the amount of permafrost-free land available is greatly reduced and this has forced many home-builders, determined to build houses close to Fairbanks (in marketable locations), toward the boundaries between "good ground" and frozen ground. These in-between areas are especially hazardous. A small deposit of ice rich frozen soil under a single corner of the building is more than enough to cause considerable damage along with the associated headache and grief to the property owner.
In the safer areas where permafrost was rarely encountered, historically, one or two boreholes for a modest building was the accepted standard for many years. But as the "good ground" was developed and development continued toward questionable areas, a increasing number of distressed foundations made it clear that the areas bounding permafrost areas (and generally mapped as "permafrost free") could contain mostly non-frozen ground with localized pockets of frozen material that were themselves large enough to damage a home.
Consequently, limiting drilling to two building corners meant the other areas were left to chance and in some areas, the likelihood of changing conditions was high from borehole to borehole and this fact prompted engineers (such as the author) to suggest additional exploration.
Today, a subsurface investigation can consist of any number of soil borings, depending on the size of the building and its location. While no practical number of borings can rule out all risk, a greater number of boreholes can go a long way towards reducing risks. SYNGEN's strategy towards investigating subsurface conditions in permafrost boundary areas includes the use of thermistor probes for temperature measurements to more thoroughly characterize subsurface conditions across the building footpring and reduce risk.
