The Effect of Backfilling Stiffness on the Lateral Response of Deeply Buried Pipelines: an Experimental Study

Abstract

Subsea pipelines passing through the shallow area are physically protected against the environmental, accidental, and operational loads by trenching and backfilling. Depending on construction methodology, environmental loads, and seabed soil properties, the stiffness of backfilling material may become largely different from the native ground (softer than native ground in most of the cases). The different stiffness between the backfill and native ground affects the soil failure mechanisms and lateral soil resistance against large pipeline displacements that may happen due to ground movement, landslides, ice gouging, and drag embedment anchors. This important aspect is not considered by current design codes. In this paper, the effect of trench-backfill stiffness difference on lateral pipeline-backfill-trench interaction was investigated by performing centrifuge tests. The soil deformations and failure mechanisms were obtained by particle image velocimetry (PIV) analysis. Three experiments were conducted by using three different backfills including loose sand, slurry, and chunky clay that represent the purchased, natural in-fill, and pre-excavated materials, respectively. The study shows that the current design codes underestimate the lateral soil resistance for small to moderate pipe displacements inside the trench and overestimate it for large lateral displacement, where the pipeline is penetrating into the trench wall.

Keywords

Lateral pipe-soil interaction / Pipeline-trench bed interaction / p-y response / Large deformation / Centrifuge testing

References

[1] ALA (2005) Guidelines for the design of buried steel pipe. American Lifelines Alliance, a partnership between FEMA and ASCE, 68-72. https://www.americanlifelinesalliance.com/pdf/Update061305.pdf

[2] ASCE Committee (2014) Soil parameters for assessing axial and transverse behaviour of restrained pipelines—Part 2: Transverse behavior. Pipelines 2014: From Underground to the Forefront of Innovation and Sustainability, ASCE, Portland, 1849–1863. https://ascelibrary.org/doi/abs/10.1061/9780784413692.167?src=recsys

[3] Burnett AJ (2015) Investigation of full scale horizontal pipe–soil interaction and large strain behaviour of sand. MSc. thesis, Queen’s University Kingston, Ontario, Canada. http://hdl.handle.net/1974/12722

[4] Chaloulos YK, Bouckovalas GD, Zervos SD, Zampas AL. Lateral soil-pipeline interaction in sand backfill: effect of trench dimensions. Comput Geotech, 2015, 69: 442-451

[5] Das BM, Seeley GR (1975) Uplift capacity of buried model piles in sand. 101(GT10), 91–94. https://trid.trb.org/view/35387

[6] DNVGL-RP-F114 (2017) Recommended practice for Pipe-soil interaction for submarine pipelines. Det Norske Veritas. Oslo. Norway

[7] Hansen JB (1948) The stabilizing effect of piles in clay. CN Post No. 3, Christiani and Nielson, Copenhagen, Denmark, November, 14–15.

[8] Hansen JB, Christensen NH. The ultimate resistance of rigid piles against transversal forces, 1961, Copenhagen: Geoteknisk Institut

[9] Kianian M, Shiri H. The influence of pipeline-trench bed interaction intensity on lateral soil resistance and failure mechanisms. Int J Geotech Eng, 2019, 14(7): 752-765

[10] Kianian M, Esmaeilzadeh M, Shiri H (2018) Lateral response of trenched pipelines to large deformations in clay. Offshore Technology Conference. Houston. Texas. USA. May 2018. OTC-28842-MS, 1–4. https://doi.org/10.4043/28842-MS

[11] Merifield RS, Sloan SW, Yu HS. Stability of plate anchors in undrained clay. Géotechnique, 2001, 51(2): 141-153

[12] Paulin M (1998) An investigation into pipelines subjected to lateral soil loading. PhD. thesis, Memorial University of Newfoundland, St. John’s, Canada

[13] Phillips R, Nobahar A, Zhou J (2004) Trench effects on pipe-soil interaction, Proceeding of International Pipeline Conference, Calgary, Alberta, Canada, IPC2004-141

[14] PRCI (2009) Guidelines for constructing natural gas and liquid hydrocarbon pipelines through areas prone to landslide and subsidence hazards. In Pipeline Research Council International. Chantilly. VA. USA

[15] Randolph MF, Houlsby GT. The limiting pressure on a circular pile loaded laterally in cohesive soil. Géotechnique, 1984, 34(4): 613-623

[16] Rowe RK, Davis EH. The behaviour of anchor plates in clay. Géotechnique, 1982, 32(1): 87-101

[17] Schiffman RL. The consolidation of soft marine sediments. Geo-Mar Lett, 1982, 2(3–4): 199-203

[18] Stanier SA, Blaber J, Take WA, White DJ. Improved image-based deformation measurement for geotechnical applications. Can Geotech J, 2016, 53(5): 727-739

[19] Stewart DP, Randolph MF. T-bar penetration testing in soft clay. J Geotech Eng, 1994, 120(12): 2230-2235

[20] Tschebotarioff GP (1973) Foundations, retaining and earth structures. McGraw-Hill Book Company, New York, 340–365

[21] Wantland GM, Consultants W, Kalajian EH. Pipeline lateral stability in soft clay. Offshore Technol Conf, 1979, 34: 217-220

[22] White DJ, Take WA, Bolton MD. Soil deformation measurement using particle image velocimetry (PIV) and photogrammetry. Geothechnique, 2003, 53(7): 619-631

[23] White DJ, Gaudin C, Boylan N, Zhou H. Interpretation of T-bar penetrometer tests at shallow embedment and in very soft soils. Can Geotech J, 2010, 47(2): 218-229