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 tfoundation, additional subexcavation to a depth belowthe anticipated base of thermokarsts and ice wedges wascompleted and the base of the excavation probed on a tightgrid for additional thermokarst voids and ice. The northernfoundation wall of the structure was redesigned as a deepgrade beam that could span localized settlement in the eventundetected thermokarsts were present.Harper BuildingThe Harper Building is near the southern edge of thecampus along Geist Road. The building is on the floodplainat the leading edge of the silt fan in an area of meander scars.Ice-rich organic silts and inorganic silts were encounteredto depths averaging about 3.6 m. Localized peat depositsoccurred at the site outside the building footprint. Thawunstablesand and silty sands extended to depths averaging7.3 m; slightly thaw-unstable gravels occurred below thisdepth. The building is founded on steel pipe adfreeze pilesbearing in the underlying gravels. The structure was designedto be elevated to provide a free air space beneath the buildingand protect the permafrost from thawing.Since construction, the free air space of the structure wasskirted and passively heated, resulting in more than 60 cmof differential settlement beneath the pile and grade-beamsupportedfloor. Connections to buried utilities, not designedto withstand building settlement, have reportedly failed.Landscaped areas and driveways have experience significantamounts of differential settlement.on highly thaw-unstable slough deposits at the leading edgeof the silt fan. The southern abutment subsequently settledapproximately 1 m, rendering the bridge unsafe.A new access road to the university (Thompson Drive)was constructed across permafrost terrain in 2005 and 2006.The majority of the alignment is located on silt fan deposits,which are perennially frozen and slightly to moderatelythaw-unstable. Cleared farm fields were thawed to a depthof 9 m.Thompson Drive was constructed using experimentalpassive refrigeration systems in areas underlain by shallowpermafrost, including a system of insulation, nonfrostsusceptiblefill, and hairpin thermosyphons completelyburied in the road bed at the southern end of the project,shoulders ventilated with a layer of coarse rock in the centerof the project, and an air convection embankment at thenorthern end of the project. The bridge over the railroad isfounded on permafrost schist bedrock, and alluvial sandsand gravels underly the site.ReferencesPewe, T.L. & Bell, J.W. 1976. Map Showing FoundationConditions in the Fairbanks D-2 SW Quadrangle,Alaska. U.S. Geological Survey Map I-829-E.Main Entrance RoadsThe main entrance to the university at time of the lastpermafrost conference in Fairbanks in 1983 was alongFairbanks Street off Geist Road. A four-lane overpass wasconstructed at the railroad tracks along this access. The centerspan of the three-span bridge is supported on strip footingsfounded on colluvium and shallow bedrock. The bridgeabutments were founded on continuous footings bearing inthe embankment fill on either side of the tracks. The northabutment and center piers were founded on thaw-stable soils,whereas the southern approach embankment was constructedFigure 1. UAF campus and terrain units mapped by Pewe (1976).352