Interaction forces between pipelines and submarine slides — A geotechnical viewpoint

Assessment of interaction forces between deep water pipelines and potential submarine slides, debris flows and turbidity currents is an important aspect of geohazard studies. Historically, interaction forces have tended to be expressed in terms of drag factors, within a traditional fluid mechanics framework, with the drag factors depending strongly on an equivalent Reynolds number for the non-Newtonian debris material. Here, we have followed a more geotechnical approach, allowing the interaction forces to be expressed in terms of a strain-rate dependent shear strength of the debris material, and with the inclusion of a drag term (with fixed drag coefficient) for high velocity, low strength, combinations. This superposition approach treats separately the interaction forces that arise from the strain-rate dependent strength and the inertia of the debris, rather than combining them into a single drag force. A failure envelope is proposed, allowing axial and normal interaction forces to be estimated for any angle of attack of the debris flow.

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► Approach for estimating debris flow impact on pipelines, combine geotechnical resistance with rate-dependent shear strength.
► And fluid drag forces proportional to stagnation pressure.
► Comparison of numerical data with theoretical values for extreme cases of normal and tangential flow directions.
► Yield envelope approach introduced for evaluating impact forces at any angle relative to the pipe (see illustration).