**Author details**

of much ongoing research, particularly with respect to fatigue and interaction with the seabed at the TDP. The current SCR's analysis is performed using simplified pipe-seabed interaction models and disregards the SCR's embedment into the seabed as well as soil suction effects in the TDZ; this will affect the predicted SCR response. Previous experiments showed that the soil suction effect can increase the bending stress of SCRs in the TDZ. The predominant offshore soil condition in a deepwater environment is soft clay soil with small undrained shear strength. Field observations have introduced that the trench is a common feature due to the SCR pipe penetration into the seabed. However, there are few published literatures that investigate the trenching effects of the riser pipe in the TDZ on the SCR's dynamic

*Geotechnical Engineering - Advances in Soil Mechanics and Foundation Engineering*

Seabed stiffness degradation due to cyclic motion is an important parameter in order to estimate the SCR fatigue in the TDZ. This aspect is not well investigated, and the seabed is traditionally not properly modelled in the current SCR fatigue analysis. Existing literature has introduced that fatigue damage is highly sensitive to the soil model utilised in the fatigue estimation calculation. The seabed non-linear model, to simulate the SCR-seabed interaction, has been shown to be more sophis-

• Although a linear seabed model is the common modelling for seabed response [9, 47, 55], which is too simplified to capture the nature of SCR-seabed interaction, SCR-seabed interaction is a considerably non-linear phenomenon. For better understanding of SCR behaviour and reliable prediction of the fatigue life in the TDZ, a numerical study and analysis of SCRs with vessel

• Fatigue performance assessment of the SCR in the TDZ remains a serious design challenge for SCR behaviour. Despite some research papers presenting a reduction in fatigue damage [34, 40, 50] due to riser embedment in the TDZ, other studies have proposed an increase in fatigue damage [7, 49]. These confounding results due to different geotechnical parameters have been imposed with trenches. The trench deepening, gradual embedment of the riser and soil stiffness have an important influence on the SCR's fatigue life in the TDZ. Furthermore, the soil parameters used in riser-seabed analysis can have a significant effect on fatigue life of SCRs. Therefore, SCR's fatigue damage in the TDZ is a critical design aspect where geotechnical consideration becomes

• Although lateral movements of the SCR can influence the riser performance, as suggested by [42, 49], the adduced SCR-seabed interaction analytical models regard only the vertical SCR motions and neglect lateral soil friction, as

The aforementioned research gap points are subjected to ongoing research and

The interested engineer or researcher will find here the necessary background on the geotechnical interaction model for SCR issue, and then will be able to proceed

ticated compared to those SCR-seabed interactions with linear soil springs. It can be concluded from the summary of models presented in the existing

structural behaviour and fatigue performance.

motions should be performed;

literature survey that:

important; and

**6. Conclusion**

**62**

presented by [40, 41].

investigations and being tackled by the authors.

Hany Elosta Subsea SURF Lead, TechnipFMC, Lysaker, Norway

\*Address all correspondence to: hanyelosta@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
