The Norman Wells pipeline has operated for over 20 years, transporting crude oil from Norman Wells, Northwest Territories to Zama, Alberta. The pipeline route traverses 869 km of discontinuous permafrost. The stability of the slopes along the route required that rapid thawing of ice-rich permafrost be avoided, lest the high porewater pressures that develop on thawing would cause instability. To reduce the thawing rate, a layer of wood chips was used as surface insulation. Approximately one-half of the insulated slopes were instrumented with thermistors and piezometers to monitor the thawing and the development of porewater pressures. This paper compares the actual performance of the insulated and non-insulated slopes to the original design predictions. Thaw depth is presented in terms of the square root of time. The likely original design intent of insulated sites was to restore a level of surface insulation that would represent a “cleared but otherwise undisturbed surface condition”. The actual performance of most of these sites was more dramatic than this. Factors that may have contributed to the greater than expected thawing are examined, including site orientation, preclearing, and soil type.

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