Flowable Backfill with Flexible Pipe in Trench Condition and FEM Verification

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by Sungro Cho, P.E., Ph.D., Project engineer; InTEC, Austin, Texas, 78720, scho@mail.uh.edu,
C. Vipulanandan, P.E., Ph.D., Professor; Chairman and Director, Center for Innovative Grouting Materials and Technology (CIGMAT), Department of Civil and Environmental Engineering, University of Houston, Houston, TX 77204-4003, cvipulanandan@uh.edu,

Document Type: Proceeding Paper

Part of: Pipelines 2005: Optimizing Pipeline Design, Operations, and Maintenance in Today's Economy

Abstract: In this study, load-deflection relationship for flexible pipe in trench condition was investigated. A soil box test was performed to investigate the behavior of flexible pipe with flowable backfill. Test was conducted using an 200 mm (8 inch) diameter flexible pipe in a trench condition, 2.25 times the diameter of the pipe. Flowable fill with unconfined compressive strength of about 75 psi (28 days) was used as backfill. After a day of curing, a maximum surface vertical stress of 770 kPa (112 psi) was applied. The pipe deflection, in-situ soil stresses, and strains in the pipe walls were measured during backfilling, and surface loading during the two months of testing. The vertical deflection in the pipe with flowable backfill during installation was — 0.03 % (extension) whereas after applying a surface loading of 770 kPa (112 psi) it was 1.0 % (shortening). The elastic modulus of backfill, Poisson's ratio of backfill, axial stiffness of pipe, interface friction angle between backfill and soil box and soil box width were important parameters in predicting the pipe deflection and stresses in the pipe using the finite element method.

Subject Headings: Pipelines | Backfills | Trenches | Soil stress | Verification | Finite element method | Displacement (mechanics) | Soil modulus | Vertical loads |

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