RESEARCH / DEVELOPMENT / TECHNOLOGY PIPELINE TECHNOLOGY JOURNAL 57 To do so, periodic submarine inspections and regular bathymetry studies must be conducted, in order to de- termine and identify critical span lengths; additionally, constant metocean parameters variations and weath- er forecast monitoring must be rigorously done, since accuracy on obtaining these variables is vital to models’ representativeness. References • Christian, H., Woeller, D., Robertson, P.K. and Courtney, R.C. (1997) ‘Site investigations to evaluate flow • • liquefaction slides at Sand Heads, Fraser River delta’, Canadian Geotechnical Journal, 34(3), pp. 384-397. Foda, M. and Hunt, J. (1993) ‘A nonlinear model for the fluidization of marine mud by waves’, Journal of Geophysical Research, 98(C4), pp. 7039-7047. Jia, Y., Zhang, L., Zheng, J., Liu, X., Jeng, D.-S. and Shan, H. (2014) ‘Effects of wave-induced seabed lique- faction on sediment re-suspension in the Yellow River Delta’, Ocean Engineering, 89, pp. 146-156. • Marín, A. (2015) “Dynamic behaviour of shallow water pipelines due to seabed liquefaction”, Thesis for MSc in Pipeline Engineering Degree, Newcastle University. • Ulker, M. (2009) ‘Dynamics of saturated porous media: Wave induced response and instability of seabed’ Rahman, M. and Guddati, M. ProQuest, UMI Dissertations Publishing. • Ulker, M.B.C. (2012) ‘Pore Pressure, Stress Distributions, and Instantaneous Liquefaction of Two-Layer Soil under Waves’, J. Water. Port Coast. Ocean Eng.-ASCE, 138(6), pp. 435-450. • Ulker, M.B.C. and Rahman, M.S. (2009) ‘Response of saturated and nearly saturated porous media: Dif- ferent formulations and their applicability’, International Journal for Numerical and Analytical Methods in Geomechanics, 33(5), pp. 633-664. • Ulker, M.B.C., Rahman, M.S. and Jeng, D.S. (2009) ‘Wave-induced response of seabed: Various formula- • • tions and their applicability’, Applied Ocean Research, 31(1), pp. 12-24. Teh, T., Palmer, A., Bolton, M.D. and Damgaard, J. (2006) ‘Stability of Submarine Pipelines on Liquefied Seabeds’, Journal of Waterway, Port, Coastal and Ocean Engineering, 132(4), pp. 244-251. Teh, T.C., Palmer, A. and Damgaard, J. (2003) ‘Experimental study of marine pipelines on unstable and liquefied seabed’, Coast. Eng., 50(1), pp. 1-17. • Wang, J., Zhang, B. and Nogami, T. (2004) ‘Wave-induced seabed response analysis by radial point interpolation meshless method’, Ocean Eng., 31(1), pp. 21-42. • Zienkiewicz, O., Chang CT, Bettess P. 18 (1981) ‘Drained, undrained, consolidating and dynamic behaviour assumptions in soils: Zienkiewicz, O C; Chang, C T; Bettess, P Geotechnique, V30, N4, Dec 1980, P385–395’ Chang CT, B.P., pp. 48-4 Author Figure 10: Difference between pipeline´s dynamic behaviour assuming seabed as an incompressible fluid (blue curve) and after calculating seabed dynamic response (red curve) Finally, Figure 10 plots dynamic behaviour variation once liquefied soil is assumed as an incompressible fluid, and once seabed dynamic response is calculated by means of skeleton-pore water flow coupled model. CONCLUSIONS After modelling, differences between pipeline’s dynam- ic behaviour assuming liquefied seabed as an incom- pressible fluid, and after calculating seabed response as contact pressures over the pipe, were recognised. Found results differs from conducted by Teh et al. (2006) and Marín (2015), where large diameter pipelines (i.e. heavy pipelines) show trends on their dynamic behaviour once seabed support is lost, governed by their own weight, inertial moment, angular frequency and oscilla- tion amplitude, regardless dynamic seabed response. Alejandro Marín Oleoducto Central S.A (OCENSA) Senior Integrity Engineer Alejandro.marin@ocensa.com.co Behaviour abovementioned is potentially influenced by D/t ratio, due to as previously stated, in spite of being a large diameter pipeline, associated mass is low regarding its reduced thickness value. The latter, since external hydrostatic pressure requirements for Ocensa´s 42” offshore pipeline are low related to its shallow water location. Therefore, a potential of being influenced by liquefied seabed response under influence of wave cyclic loads, for the studied pipeline may be suggested. In this way, it is recommended to complete soil-pipeline interaction mod- els once integrity and maintenance plans are undertaken. Finally, it is also recommendable to complement soil-pipeline interaction models with Vortex In- duced Vibration (VIV) analysis, addressing to identify potential pipeline damage associated to fatigue induced by cyclic stresses.