The soil response around a high temperature pipeline proposed for construction in northern Alberta was evaluated. The objective of the field testing program was to gain a better understanding of the engineering properties of the backfill material placed in the trench around a pipeline when subjected to cyclic loading. This is required for the strength and stiffness of these backfill materials in order to improve the predictions related to pipe restraint and movements of the pipe during the cyclic loading anticipated from the thermal cycles.

Specialized field tests were carried out to measure the stiffness of backfill materials within the trench and of the undisturbed native material. Tests were completed along the proposed right-of-way in the native undisturbed soils and then repeated in the “fresh” backfill materials. In addition, field tests were completed over an existing pipeline to assess the effects of “aging” on the backfill materials. Overall, the test results show a significant reduction in the strength and stiffness of the backfill materials as well as a moderate improvement as the materials age with time. However, even “aged” backfill has a much lower strength and stiffness when compared to the native undisturbed soils. The results from the field testing program were incorporated into the numerical models being used to evaluate the performance of the pipeline.

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