TRANS ALASKA PIPELINE 800 mile Trans Alaska Pipeline system (TAPS) stretches from Prudhoe Bay to Valdez in North America Pipeline Transports crude oil Constructed between 1975 and 1977 Cost $8 billion for entire system Crosses three mountain ranges and over 800 rivers Extreme geological conditions including permafrost and arctic tundra formations BACKGROUND: Pipeline location:

TRANS ALASKA PIPELINE GEOLOGICAL CONSIDERATION: Presence of PERMAFROST both Continuous and Discontinuous PERMAFROST: Soil or Rock, with or without included water, which has remained at or below 0°c for 2 or more years Presence of permafrost along the Trans Alaska Pipeline Permafrost cross section

TRANS ALASKA PIPELINE STRUCTURE OF PERMAFROST: Varying depths of permafrost presence up to 200m depth The Active layer: Fluctuates below freezing during the year Ground water movement within the active layer effecting stability Thick snow layer will act as and insulator Formation of Ice wedges Important to classify type of ground ice present in permafrost as this will effect ground strength

TRANS ALASKA PIPELINE PROBLEMS CAUSED BY PERMAFROST GEOLOGY: Thaw settlement: Thermal change in the ground caused by the construction of pipeline. Frost Heave: Ground heaves during freezing periods Heterogeneity: Unstable formation of permafrost Thaw settlement on pipe section

TRANS ALASKA PIPELINE Pipeline sensitive to movement – ruptures or leaks lead to Environmental Problems ISSUES CAUSED BY THE PRESENCE OF PERMAFROST GEOLOGY: Instability: Instability of the ground within the active layer during periods of freezing and unfreezing. Surface ground settlement, subsidence Construction: Construction problems in frozen ground, unpredictable ground ice structures Ground ice is always present in this climate Support settlement ENGINEERING SOLUTIONS FOR PIPELINES IN PERMAFROST:

TRANS ALASKA PIPELINE POSSIBLE ENGINEERING SOLUTION: Control Thaw Settlement: Run the pipeline hot or cold? Areas of discontinuous permafrost this is a problem. Thaw bulb created around the pipeline where thermal transfer warms ground Methods to control thermal transfer and reduce settlement Thaw bulb created around buried pipe Insulation: Cover ground with material such as wood chip, slow thawing process.

TRANS ALASKA PIPELINE Passive cooling: Installation of pipes through areas around pipeline to cool ground and remove thermal heat Air is lower thermal conductivity and so use wind to remove heat Thermosyphon: Heat exchange system Keep the ground Frozen: Ground Freezing Techniques: Refrigeration plants on surface Aware of the impact of frost heave Frost heave damage Passive cooling installation

TRANS ALASKA PIPELINE SOLUTIONS ADOPTED ON TRANS ALASKA PIPELINE: Used a combination of techniques, Above ground Below ground, thaw settlement control. Above ground: Where thaw-stable soils were identified pipeline was buried in a conventional manner, thaw settlement was managed with the use of woodchip insulators Conventional below-ground — 376 miles Unstable thaw areas where thermal transfer may cause thawing and instability in the ground Refrigerated below-ground — 4 miles Cross section of conventional pipe Below ground section

TRANS ALASKA PIPELINE Above Ground: Supported Pipeline above the ground Above-ground — 420 miles Consider settlement of supports: specially design 2 inch heat pipes act as a thermosyphon to remove heat from the system Design of supports Section of pipeline running above ground

TRANS ALASKA PIPELINE ANY QUESTIONS ?