United States Department of Transportation
i
Geotechnical Asset Management (GAM) Through Thermal Modeling and Post-Construction Thermal Monitoring of Highway Embankments for the Dalton Highway MP 0-9 Project
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2019-08-01
[PDF-10.20 MB]
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Edition:Final, 2019
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Abstract:Geotechnical Asset Management (GAM) involves geotechnical features that can affect the performance of a transportation system and includes the design and construction of road embankments to achieve lowest possible life-cycle asset costs. Road embankments constructed on ice-rich permafrost must promote a thermally stable subgrade in order to minimize thaw settlement and related long-term road maintenance costs. The Dalton Highway MP 0-9 Reconstruction Project is planned to realign and reconstruct the first nine miles of the Dalton Highway. The first six miles are a new road alignment over foundation soils that include sections of very ice-rich silt and peat and also massive ice. Longterm performance of the realignment will be dependent upon design and construction of an embankment that maintains permafrost in the foundation soils. Alaska Department of Transportation and Public Facilities (DOT&PF) Northern Region Materials Section (NRMS) staff has used GeoStudio TEMP/W, a commercially available two-dimensional finite element computer software program, to construct thermal models of conventional and insulated embankments in an effort to design road embankments that reduce the thawing of ice-rich permafrost in the road subgrade. Key results include: (1) The thermal model developed for the pre-embankment conditions corresponded well with measured ground temperatures and measured thaw depth. (2) There was little difference in thaw depth measured between undisturbed areas and locations of winter-only equipment travel. There was a doubling of the thaw depth between undisturbed areas and the locations of summer equipment travel / drilling operations. (3) Observation of near-surface ground water conditions in test pits provided a mechanism for understanding the observed bi-annual “flat-lining” of near-surface ground temperatures. (4) Measurement of near-surface ground temperatures allowed for calculation of seasonal n factors for tundra ground cover. (5) There was good agreement between soil material thermal properties estimated by the methods found in A Generalized Thermal Conductivity Model for Soils and Construction Materials – Côté & Konrad (2005) and traditional estimation methods used by Kersten and Johansen. (6) Measured soil temperature at various depths allowed for the thermal model to be calibrated by adjusting the soil material thermal properties until modeled cumulative thawing and freezing degree-days matched the measured cumulative thawing and freezing degree-days at depth. The research program and associated literature review has resulted in changes and refinements to DOT&PF’s thermal modeling procedures.
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