American Society of Civil Engineers


Active Layer and Frost Bulb Interaction for a Full-Scale, Buried Chilled Gas Pipeline


by Margaret M. Darrow, Ph.D., (Department of Mining and Geological Engineering, University of Alaska Fairbanks, P.O. Box 755800, Fairbanks, AK 99775-5800 E-mail: ffmmd@uaf.edu)

pp. 99-109, (doi:  http://dx.doi.org/10.1061/41072(359)12)

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Document type: Conference Proceeding Paper
Part of: Cold Regions Engineering 2009: Cold Regions Impacts on Research, Design, and Construction
Abstract: Recent economic trends have sparked renewed interest in the development of a gas pipeline to transport natural gas from Alaska’s North Slope to markets in the contiguous United States. A buried chilled gas pipeline is a suitable design choice because of safety and environmental concerns. One major drawback is the interaction of the frost bulb with unfrozen, frost-susceptible soils. From 1999 to 2003, the University of Alaska Fairbanks and Hokkaido University in Japan ran a joint experiment to study the behavior of a full-scale, buried chilled gas pipeline. The pipeline, located outside of Fairbanks, Alaska, was constructed across a permafrost/non-permafrost boundary, in order to study the upheaval and stresses induced in the pipe due to differential frost heave. This paper details a small component of this project, namely the interaction between the frost bulb and the active layer immediately above the pipe. The temperature interaction at this interface was modeled using TEMP/W, a two-dimensional finite element program. Analysis of the model results indicates that the modeled temperatures correspond well to measured temperatures. The model results also indicate that at several times during the summer months, the frost bulb above the pipe was dramatically thinned due to spikes in the pipeline gas temperature. Coupled with cumulative stresses created in the pipe due to differential heave, this may result in loss of pipe structural integrity and ultimate failure. These results suggest that burial depth and the type of foundation soil present are critical elements of the final pipeline design.


ASCE Subject Headings:
Buried pipes
Gas pipelines
Frost
Alaska