Field Testing of Pipeline Trench Backfill Properties Placed during Winter Conditions

Rodney McAffee, Ryan Phillips, Michael Martens

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Cold Regions Geotechnics

ABSTRACT: ing of Pipeline Trench Backfill Properties Placed during Winter Conditions Rodney McAffee and Ryan Phillips C-CORE, St. John's, Newfoundland and Labrador, Canada Michael Martens TransCanada Corporation, Calgary, Alberta, Canada ABSTRACT The soil-structure interaction of a high temperature pipeline and the backfill materials being constructed in the winter is being evaluated. The objective was to better understand the engineering properties of the backfill material placed around a pipeline when subjected to cyclic thermal loading. Field tests were carried out to measure the stiffness of backfill materials within the trench. The temperature of the material when stockpiled was monitored before being placed back into the excavation. In addition, backfilling procedures were followed to avoid the placement of any frozen material. A similar testing program was completed in the summer where both 'fresh' backfill materials and native undisturbed soils were tested at the same location. Overall, the test results show a significant reduction in the strength and stiffness of the backfill materials when compared to the native undisturbed soils. RÉSUMÉ La réponse du sol lors de la construction hivernale d'un pipeline à haute température est évaluée. L'objectif est de mieux comprendre les propriétés d'ingénierie du matériau de remblai placé autour du pipeline lorsqu'il est soumis à un chargement cyclique. Des essais sur le terrain ont été menés afin de mesurer la rigidité des matériaux de remblai composant la tranchée. La température du matériau mis de côté a été mesurée avant que ce dernier ne soit placé à nouveau dans l'excavation. Aussi, des procédures de remblayage ont été suivies afin d'éviter que des matériaux gelés ne soit utilisés dans le remblai. Un programme semblable a été effectué au cours de l'été durant lequel des matériaux de remblais ‚frais' et des matériaux de remblais non perturbées ont été testés au même emplacement. Globalement, les résultats démontrent une réduction significative de la résistance et de la rigidité des matériaux de remblai comparativement aux sols non perturbés. 1 INTRODUCTION A high temperature pipeline that will be subjected to thermal cycling is proposed to be constructed in northern Alberta. Very little information is available within the literature quantifying the behavior of relatively loose backfill materials, in particular when the material is placed during winter conditions. Field tests were completed to gain a better understanding of the engineering properties of the backfill material placed in the trench. Typically, trench backfill is loosely placed around the pipe and only tamped or 'tracked' with low ground pressure equipment once the backfill is of sufficient height above the pipe. During winter construction, efforts are made to prevent or minimize the placement of any frozen materials around the pipe during backfilling. The final surface above the trench is usually crowned to account for some self-weight settlement. The degree of densification related to the self-weight settlement is expected to be limited, especially at depth. Two field testing programs were undertaken to measure the stiffness of the backfill materials within the trench and of the native undisturbed soils. The first program was completed during the summer where tests were also completed over an existing pipeline in the same area to assess the effects of 'aging' on the backfill materials. The second field testing program was carried out during cold weather conditions in the winter to evaluate how soil stockpiles freeze, whether any frozen backfill gets placed back into the trench during backfilling and whether this affects the stiffness of the backfill materials when compared to the results measured during the summer. This paper presents the results of the two field testing programs and compares the stiffness of 'fresh' (warm and cold weather construction) and 'aged' backfill materials and how they compare to the native undisturbed soils. 2 TESTING LOCATIONS AND SOIL CONDITIONS Three test locations were selected where the field testing could also be performed on an adjacent existing pipeline right-of-way and on the proposed alignment. The close proximity of the existing pipeline to the proposed alignment (within 50 to 100 m) allowed for a comparison of 'fresh' backfill, 'aged' backfill, and native undisturbed soils at each test location. In total, 10 tests were undertaken along the existing right-of-way and 24 tests on the proposed alignment as part of the summer field testing program. In contrast, the winter field testing program consisted of only 7 tests completed in 'fresh' backfill at only one of the test locations. The soil conditions at two of the sites were found to consist of sandy soils. The soils were classified as silty sand (SM) or clayey sand (SC) with approximately 20% to 50% fines content. The in-situ density of the sandy soils for 'aged' and 'fresh' backfill materials covered a wide range of densities from a low of 1440 kg/m3 to a high of

RÉSUMÉ: Testing of Pipeline Trench Backfill Properties Placed during Winter Conditions Rodney McAffee and Ryan Phillips C-CORE, St. John's, Newfoundland and Labrador, Canada Michael Martens TransCanada Corporation, Calgary, Alberta, Canada ABSTRACT The soil-structure interaction of a high temperature pipeline and the backfill materials being constructed in the winter is being evaluated. The objective was to better understand the engineering properties of the backfill material placed

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Cite this article:
Rodney McAffee; Ryan Phillips ; Michael Martens (2014) Field Testing of Pipeline Trench Backfill Properties Placed during Winter Conditions in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper391,author = Rodney McAffee; Ryan Phillips ; Michael Martens,title = Field Testing of Pipeline Trench Backfill Properties Placed during Winter Conditions,year = 2014}