Where a cold pipeline through discontinuous permafrost crosses from frozen (non-heaving) ground to unfrozen (heaving) ground, differential frost heave may occur adjacent to the thermal transition. If the differential heaving occurs over short distances, then the resulting strains and curvatures induced in the pipe may be of concern. The induced curvature will be strongly dependent on the amount of heave, and the magnitude of the resistance to uplift imposed by the frozen soil on the nonheaving side of the transition. There are three primary geotechnical components in the design process for northern pipelines in frost heaving terrain, i.e.
thermal interfaces,
pipeline frost heave and
uplift resistance.
This paper briefly summarizes the data available for the frequency and distribution of thermal interfaces in discontinuous permafrost. A new frost heave theory for soils in one dimension is then reviewed. The theory is then extended to two dimensions, suitable for application to the northern pipeline design issue. Finally, methods of estimating and applying the frozen soil uplift resistance component in northern pipeline design are reviewed.
Since the early 1970's, several oil and gas pipelines to transport Arctic hydrocarbon reserves to southern markets have been proposed. To date, two have been built, i.e. the large diameter Trans-Alaska Oil Pipeline across Alaska, and the small diameter oil pipeline from Norman Wells NWT to Zama Lake terminal in Northern Alberta. The first of these is a hot oil line that involves no soil freezing, and the second is a near-ambient line that involves only minor amounts of soil freezing induced by the pipeline. Several other pipelines using different routings along the Mackenzie Valley and the Alaska Highway have been proposed (See Figure 1).
