Ninth International Conference on Permafrost ... - IARC Research

Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tFigure 2. Typical frost-protected shallow foundation section.The climate parameters for Fort Wainwright are outsidethe ASCE design standard for the design and constructionof frost-protected shallow foundations. In addition,discontinuous permafrost underlies portions of the site. Todetermine the insulation requirements for a frost-protectedfoundation design in areas without permafrost, thermalanalyses were conducted using Temp/W, a finite elementsimulation package developed by Geoslope <strong>International</strong>,Inc., in Calgary, Alberta. Based on the results of the analyses,we recommended a 100-mm-thick wing of insulation, 1.22m wide, extending out horizontally from the base of thefoundation around the entire perimeter of the frost-protectedslab foundations.Complete excavation of frost-susceptible soils wasrecommended in permafrost areas.Temporary Frost Protection StrategiesThe short construction season placed limitations on theschedule for such a large construction project. Foundationsthat had been started had to be heated by the end of theconstruction season to prevent frost-susceptible foundationsoils from freezing. Furthermore, deep seasonal frost woulddelay foundation construction in the spring. The followingstrategies were considered to reduce the affects of seasonalfrost on the construction schedule:1. Complete removal of frost-susceptible soils belowplanned foundations.2. Use of board insulation, laid horizontally acrosspads and recycled the following spring for use as slab andfoundation insulation.3. Use of on-site soils or chipped organics as insulationover building pads designed for frost-protected foundations.4. Continuous heating of pads and foundations throughoutwinter with glycol heating loops.Using a combination of these strategies, the majority of thefoundations were prepared in the first construction season.The following spring, construction began without the needto wait until the seasonal frost had thawed, effectively andefficiently achieving the desired outcome for temporary frostprotection.Figure 3. Foundation monitoring temperature data.Foundation MonitoringLittle data is available on the use of on-site organics toprovide temporary frost protection for a construction project;therefore, two prepared foundation pads were instrumentedwith thermistor strings and monitored for temperatures overthe winter, in addition to monitoring air temperatures.Woody plants, including small trees up to 0.3 m in diameter,were chipped/shredded during the 2007 construction season.Selected pads were covered with roughly 1 m of this materialwhich was then covered with plastic sheeting to reduce thepotential for natural convection. Thermal simulations wereconducted to assist the contractor in determining the thicknessof recycled on-site organics necessary for temporary frostprotection.Temperatures were monitored throughout the 2007/2008winter. The temperatures plotted in Figure 3 show thatthe chips were effective at preventing building pads fromfreezing. Figure 3 also suggests some possible heat generationdue to organic decomposition.ReferencesAmerican Society of Civil Engineers (ASCE). 2001.Design and Construction of Frost-Protected ShallowFoundations. ASCE 32-01.84