ABSTRACT
Elevated pipelines are the norm in the North Slope oilfields. Problems were observed with tilting, settling, or frost-jacking of Vertical Support Members (VSMs) supporting portions of the abovegrade piping. Further observation showed that the majority of the problems existed where the VSMs were installed in, or adjacent to, the numerous shallow ponds or lakes that dot the tundra. Ponded water causes a condition where the local permafrost is warmer than the surrounding permafrost because much of the winter's cooling is absorbed by the phase change from water to ice and then lost during the summer due to the high solar absorbance of the water surface. To further understand the magnitude of the warming condition, a drilling program was undertaken to determine subsurface soils and groundwater conditions and temperatures. From this data, a correlation was developed between the ponded water depth and the subsurface temperature profile. Subsequently, a procedure was developed to design adfreeze (standard) VSMs, Helix VSMs, and Thermo Helix VSMs in areas of ponded fresh water. This paper presents the temperature profile of the permafrost beneath ponded water and addresses the development of design procedures for these conditions.
