Abstract

The Fairbanks area is prone to many of the same geologic hazards as the more temperate parts of the state, with the added difficulties posed by the presence of discontinuous permafrost. The frozen soils can range from sands and gravels which have minor settlement potential to silts containing large masses of ice, where settlement potential is measured in feet. Even when the silty soils are unfrozen, there is the risk of settlement from the collapse of thermokarst voids, cavities which once contained ice. Construction is further complicated by the problem of frost heaving in fine-grained soils.

Much of Fairbanks occupies the floodplain of the Chena and Tanana Rivers. A shallow water table presents problems both during and after construction, and until recently, flooding was a serious threat. The alluvial deposits below the water table are often loose, presenting a risk of liquefaction or dynamic consolidation. This problem is perhaps one of the most serious related to the seismic activity of the Fairbanks area. The water table aquifer is also highly permeable, resulting in the potential for transport of contaminants. Other hydrologic problems are related to the presence of permafrost, including the formation of icings by artesian flows, and problems with water availability and sewage disposal.

Development in the hillsides surrounding Fairbanks has not yet resulted in many slope stability problems, but highway construction has shown that the potential exists. The loessial silt which blankets the hills is also highly susceptible to erosion.

Generally none of the factors described above is serious enough to preclude development if the siting and design processes carefully address the potential problems. In particular, a thorough geotechnical investigation is necessary to provide input and recommendations to the designer.