RELIABILITY BASED STIFFNESS ANALYSIS FOR APPLICATION DURING INSTALLATION OF SUCTION CAISSONS

The design of suction caissons for offshore wind turbines is generally performed deterministically, using load and resistance factors taken from relevant codes and standards. This approach has been widely accepted for the geotechnical design of suction caissons in well-characterised soil conditions. However; soil layering and properties often vary considerably from location to location within an offshore wind farm. Furthermore, the installation process can also cause changes in the soil state in the vicinity of the skirts, which will affect noticeably the response of the suction caisson during operation. While this can be considered implicitly in the geotechnical design by means of assumptions, the inherent uncertainty of the soil state will impact the overall performance of the structure considerably. On the other hand, an optimized design for the system requires an accurate prediction of the foundation stiffness. The authors present a reliability-based framework for the assessment of foundation stiffness, taking into account the most important input parameters and their expected variability. The framework can be applied both in foundation design as well as during actual installation in order to provide immediate feedback to permit adjustment or mitigation before the installation is finalized. Using a reliability-based approach in design allows an assessment of the probability of reaching the limiting design criteria and to quantify the related risk. The proposed reliability-based framework can be applied to other design aspects. This is exemplified using the example of coupled foundation installation and capacity assessment. The authors further discuss how the framework can be extended to more complex design procedures.