Earthquake Soil-Structure Interaction Assessments of Jack-Up MODU for Tangguh Development â€“ Part 2-Paper

Paper

Pdf Summary

The paper presents advanced seismic soil–structure interaction analyses for a jack-up rig at multiple sites in the earthquake-prone Tangguh development, offshore Papua Barat, Indonesia. Using conventional approaches was insufficient to demonstrate safe operation, so the study used integrated three-dimensional ABAQUS models of the rig, spudcan foundations and soil.<br /><br />For the relatively straightforward Site A, the model represented shallow spudcan embedment in dense sand over firm to very stiff clay. Nonlinear cyclic soil behaviour and earthquake loading were modelled, with site-response results checked against the NERA program. The model was calibrated to reproduce the foundation capacity established by operational preloading—a key condition for credible seismic predictions. Analyses indicated substantial rig tilt, addressed by adding 1,000 tonnes of water ballast over the bow leg. Predicted total settlements were generally 1.3–1.6 m, with differential settlement between the bow legs mostly 0.3–0.7 m; the resulting structural response was judged acceptable.<br /><br />Deeper penetration, sand layers and re-penetration into existing craters made other sites more challenging. The authors developed a two-stage method to establish realistic initial conditions. First, large-displacement finite element analyses using ABAQUS’s Coupled Eulerian-Lagrangian capability simulated spudcan penetration and extraction, crater backfilling, and re-penetration. Then, the resulting soil strengths, stresses and geometry were transferred to the seismic model using calibrated axisymmetric and three-dimensional “wished-into-place” foundation models. Mesh remapping helped limit distortion, and sand properties were adjusted to represent undrained behaviour during seismic loading.<br /><br />The study shows that carefully combining large-displacement penetration modelling with full 3D dynamic analysis can represent preloading history and foundation conditions more reliably. This approach supports site-specific assessment of jack-up performance where high seismicity makes safe operation a critical design concern.

Keywords

seismic soil-structure interaction

jack-up rig

ABAQUS

spudcan foundations

earthquake loading

offshore Papua Barat

Tangguh development

finite element analysis

foundation settlement

preloading history