WP 3 - Development of 3DSoil: library of soil interaction models for different foundations
The main objective is to develop soil interaction models to be implemented in integrated analyses for OWT. This work package is the most research-extensive WP in the project, involving one Ph.D.-student at NTNU funded by the Project, and one Ph.D. supported in-kind by NGI.
The result will be in the form of a library of models that will capture the various foundation types, load conditions, and analysis types. Methods and tools for converting raw soil data from lab tests and site investigations to input data for the soil interaction models will also be developed. This WP is divided into four tasks as described below.
Task 3.1 - Development of computational tools for foundation damping
Responsible partner: NGI, Participating partners: Equinor
Contour diagrams relating soil damping to the number of load cycles and load level will be developed. Such models are common for representing soil stiffness under cyclic loading. Typically, the damping increases with load and strain level. Furthermore, there is a need for developing numerical models that integrate the intrinsic soil damping to represent global damping on the foundation level.
Task 3.2 - Development of foundation models
Responsible partner: NGI, Participating partners: NTNU.
Soil interaction models of the type foundation models will be developed for shallow foundations (skirted foundations, gravity-based foundations, and possibly short monopiles). The models may have the same mathematical foundation (elastoplastic, hypoplastic, etc.) but still deviate in the exact functions and dependencies describing stiffness, damping, and capacity characteristics.
Several Finite Element Analyses (FEA) will therefore be carried out to serve as the basis for the formulations of the models. Among other tools, the NGI in-house soil models and procedures UDCAM and PDCAM will be used in the analyses to account for cyclic undrained and drained soil responses.
The 3D soil library will address a range of different loading and geotechnical conditions.
Task 3.3 - Development of Soil Interface models
Responsible partner: NGI, Participating partners: NTNU.
Soil interaction models of the type Soil Interface (Figure 1) will be developed for deep foundations (monopile and slender piles). The basis for the models will be advanced FE analyses.
The FEA will be able to follow the redistribution of stresses on the pile due to cyclic loading. Moreover, it will be considered to develop these models closer to the traditional nonlinear spring, dashpot, and slider elements which are routinely used by the industry.
Task 3.4 - Adaptation for practitioners
Responsible partner: NGI, Participating partners: Equinor, Vattenfall, IFE, Olav Olsen.
The models in this study will be developed with a rigorous mathematical framework hardly accessible to practitioners. The framework will be kept in the background, and a user-friendly interface will be implemented for the end users.
The models may therefore be tailor-made for a specific application, e.g FLS analyses of jacket support structure on piles or ULS analyses of monopiles to reduce the number of input data. This adaptation will be carried out in close interaction with structural engineers from partners and end-users to identify the right balance between easy usage and accuracy.
