Subsea pipelines are exposed to the risk of rockfall impacts near landfalls and outcrops of the seabed which exhibit steep and rocky features. Methodologies and tools are needed to model and assess the probability of occurrence of rockfall events, the consequences of the impact and possible protective measures. The kinematics of falling rocks has been the object of several theoretical and experimental studies. Theoretical models developed to match the results of real scale testing in air are based on the principle of conservation of energy. The dissipation due to inelastic bounces and friction are modeled by means of coefficients treated as stochastic variables to represent the randomness of rock trajectories. Added mass and drag forces are included in the subsea model; the latter require integration of equation of motion due to their dependence to velocity. The methodology has been implemented in a code proposed for risk assessment of subsea installations. The present paper briefly illustrates the basic methodological approach and presents a comprehensive case study to show the capabilities of the method, in terms of expected trajectories, histograms of run-out distances and velocities, and estimates of the probability of run-out distances exceeding the position of the pipeline. This information is used by the designers to select optimum positions of subsea pipelines and /or adopt protective measures.

Probabilistic Assessment of Rockfall Impact on Subsea Pipelines

BOOTE, DARIO;
1998

Abstract

Subsea pipelines are exposed to the risk of rockfall impacts near landfalls and outcrops of the seabed which exhibit steep and rocky features. Methodologies and tools are needed to model and assess the probability of occurrence of rockfall events, the consequences of the impact and possible protective measures. The kinematics of falling rocks has been the object of several theoretical and experimental studies. Theoretical models developed to match the results of real scale testing in air are based on the principle of conservation of energy. The dissipation due to inelastic bounces and friction are modeled by means of coefficients treated as stochastic variables to represent the randomness of rock trajectories. Added mass and drag forces are included in the subsea model; the latter require integration of equation of motion due to their dependence to velocity. The methodology has been implemented in a code proposed for risk assessment of subsea installations. The present paper briefly illustrates the basic methodological approach and presents a comprehensive case study to show the capabilities of the method, in terms of expected trajectories, histograms of run-out distances and velocities, and estimates of the probability of run-out distances exceeding the position of the pipeline. This information is used by the designers to select optimum positions of subsea pipelines and /or adopt protective measures.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11567/315761
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