Session: 06-06-03 Pipe/Soil Interactions

Paper Number: 134242

134242 - Advanced Assessment of Pipeline Subjected to Downslope Movements at River Crossing: Effect of Concrete Coating 

Abstract: 

The long linear nature of buried pipelines results in the risk of interaction with a range of geotechnical hazards including Downslope movements at pipeline stream and river crossings. Ground movement induced by these geotechnical hazards can subject a pipeline to displacement controlled axial loading, lateral and vertical and bending. These geotechnical hazards can result in the accumulation of axial tensile and compressive strains in the pipe. Compressive strains may result in local buckling/wrinkling of the pipe. The tensile strains may result in girth weld failure. therefore, calculation of pipe strain demand and strain capacity considering the site condition and the appropriate slope movement mechanism is necessary in assessing the pipeline integrity to support maintenance management.

It is a common practice to use weight concrete coating to provide negative buoyancy for river crossing application. The pipeline concrete coating design may extend to the toe of the slope and end adjacent to the pipeline location experiencing displacement (bending deformations). The discontinuity of the concrete coating can reduce the bending resistance of the pipeline locally by focussing bending strains in the steel pipe at the end of the coating due to extra bending stiffness provided by the concrete.

This can result in significant strain concentrations (local buckling/wrinkling), especially when the pipe is subject to plastic deformations.  To address this without exaggerating the stiffening effect of the concrete, it is necessary to account for pipe concrete coating damage (Cracking or spalling impacting concrete integrity) and for the slip between the concrete weight coating and the pipe.

This paper presents case studies analyses of slope movement along the pipe axis and oblique to the pipe axis using a novel 3D continuum model to illustrate the detailed information that can be derived from geotechnical hazard simulation. The model considers a pipe shell element representation, a discrete element soil representation and concrete solid element coating overtops of the steel pipe shell element representation. The model was calibrated and validated for the assessment of pipe-soil interaction modeling of geotechnical events.  The model was developed with support from the Pipeline Research Council International (PRCI) and the US Department of Transportation (US DOT).

The analyses presented in this paper provide insights into the effects of ground movement on pipeline integrity near river crossing. The analyses highlight:

·         The effects of the pipe concrete weight coating on the pipeline response at the crossing, and   

·         The effects of the slip plane angle at the toe of the slope on the slope-pipe interaction loading and pipeline response that may affect the remedial action decisions.

The results presented in this paper will be of interest to pipeline operators, geotechnical specialists, regulators and integrity management specialists.

Presenting Author: Abdelfettah Fredj BMT Canada

Presenting Author Biography: Principal engineer

Authors:

Abdelfettah Fredj BMT Canada