Ninth International Conference on Permafrost ... - IARC Research

Challenges of Infrastructure Growth on a University Campus inDiscontinuous PermafrostFrank WuttigShannon & Wilson, Inc.IntroductionThe University of Alaska Fairbanks (UAF) campus islocated in a transition zone from the southern edge of abroad upland area down onto lowlands of the Chena andTanana Rivers (Fig. 1). The campus is underlain by warmdiscontinuous permafrost.The main portions of the campus, including LowerCampus and West Ridge, are on a low east–west trendingridge overlooking the lowlands to the south. The distributionand character of the permafrost has affected and continuesto affect the development of the campus and surroundinginfrastructure.This abstract describes the geologic and permafrost settingof the campus and surrounding area, and describes some ofthe effects permafrost has had on design and construction ofcampus facilities.The majority of campus development has occurred on thecrest or southern slope of the ridge, which is generally freeof permafrost and permafrost-related features. Developmentbecomes more challenging in discontinuous permafrostareas north of the ridge crest and on the lowlands south ofthe ridge. This abstract discusses four campus infrastructureprojects impacted by permafrost, as well as challenges andlessons learned from developing the projects.Geologic and Permafrost SettingThe upland ridge is underlain by loess-covered schistbedrock, and bedrock outcrops are found at the east end ofcampus. The windblown silt is retransported downslope tothe north and south of the ridge crest. The lowlands consistof vegetated floodplains and low benches cut by the Tananaand Chena Rivers. Soils in the lowlands typically consistof interbedded alluvial sands and gravels mantled by siltyoverbank deposits dissected by filled sloughs and oxbowlakes representing former river channels.A large, low-angle fan of retransported loess emanatingfrom the nearby Cripple Creek Valley onto the lowlandcovers the southwest portion of the area. The distal (leading)edge of the silt fan is scalloped where it has been eroded byformer channels of the Chena River. Soils along the leadingedge of the fan have been mapped as silt-filled meanderscars. Terrain units mapped by Pewe (1976) are shown inFigure 1.The silt fan is generally underlain by continuouspermafrost, with a low to moderate ice content, occurringprimarily as pore ice with some segregated ice as seams andlenses.Permafrost on the floodplain is generally discontinuous.Surficial soils on the floodplain have low to moderate icecontent. The underlying sands and gravels typically havelow moisture contents.Retransported silt permafrost on the north-facing slopesand in the valley bottoms is typically perennially frozenwith moderate to very high ice content in the form of poreice, segregated ice as seams and lenses, and massive iceassociated with ice wedge deposits.<strong>International</strong> Arctic Research CenterThe <strong>International</strong> Arctic Research Center (IARC), foundedon windblown silt in the West Ridge area of the UAF campus,was originally designed to sit north of Koyukuk Drive in linewith the front of the adjacent Elvey building. A portion ofthe proposed footprint extended into a forested area northof the ridge crest. Exploratory drilling showed the area to beunderlain by discontinuous ice-rich silt permafrost. Longtermthaw settlement concerns resulted in a shift of thebuilding footprint to the south into Koyukuk Drive and areroute of the road south of the structure.In the first year following construction of the facility, thesidewalk slab in front of the main entry heaved, blocking thefront entrance. The slab was constructed on a thin layer ofnonfrost-susceptible fill overlying a frost-susceptible silt filland a silt subgrade. It was postulated that the heaving waslikely aggravated by construction water, which was used tocompact the silt fill beneath the sidewalk. Heaving has notbeen a problem in subsequent years.West Ridge Research BuildingThe multi-storied West Ridge Research Building (WRRB)is north of the Elvey Building in the West Ridge area of theUAF campus. The structure is north of the east–west trendingridge crest in an area originally developed as a parking areafor adjacent buildings. Numerous ground collapses, somemore than 7 m deep, have developed along the northern edgeof the parking lot, the result of concentrated surface runoffentering thermokarst voids in the subsurface.Subsurface exploration of the area showed the southernportion of the parking area immediately behind the ElveyBuilding had suitable conditions for a deep, conventionalfoundation consisting of thawed and low-moisture-contentsilt permafrost. The northern portion of the lot was notsuitable for construction due to known thermokarst andthaw-unstable silt permafrost. However, the footprint of thestructure was extended out into the northern portion of theparking area. During construction, large voids and massiveice representing degrading ice wedges were encountered inthe northern portion of the foundation excavation. To reducethe potential for thermokarst collapse beneath the structure351