Thermally-induced buckling analysis of pipeline interacting
with soil foundation
Keywords: finite element method
soil mechanics
pipe-soil interaction
multi-slice model
industrial case study
limit analysis
moving solution domain sequential limit analysis
centrifuge model test
multi-cyclic PSI analysis

Thermally-induced buckling analysis of pipeline interacting with soil foundation is studied numerically such that the pipe-soil interaction mechanism is investigated for the design of the deep-ocean pipeline.
To exactly capture the physics of the pipe-soil interaction in the lateral and vertical directions, a novel MSD-SLA method is developed. The MSD-SLA method utilises the moving solution domain interacting with the moving rigid body structure on top of the background domain such that the simulation efficiency is largely improved. A background-domain-based mapping algorithm is developed such that the history-dependent variables (e.g. soil strength, plastic strain) can be mapped from time step to time step to complete the sequential limit analysis. Through the validation in various 2D problems, the accuracy of the MSD-SLA method is demonstrated. The convergence study on the numerical parameters is also given, showing that the numerical results are less sensitive to the numerical parameters in the convergent intervals. The CPU time of the MSD-SLA method is also presented, showing that the proposed MSD-SLA method is indeed fast.
Then, a centrifuge model test report is assessed using the MSD-SLA method. The multi-cyclic lateral movement analyses ranging from 12 to 55 cycles are presented with generally accurate simulation results. Various engineering phenomena are investigated, e.g. the sequential lay-down, lateral breakout, cyclic lateral movement, encroachment and over-hanging soil berm. The centrifuge model test study indicates that the pipe-soil resistance force is highly complicated, showing strong connection with the soil softening effect, embedment, soil berm shape and the deformed soil free surface. From this study, the stability of the MSD-SLA method turns to be good.
The multi-slice model incorporating the MSD-SLA as the slice solver is developed for the parallelisable analysis of the 3D pipe-soil interaction problem. In the multi-slice model, the 3D problem is decomposed into a series of 2D slice models for the interaction analysis between the pipe cross-section and the 2D slice of the soil foundation. The integration algorithm between the pipe element and the slice solver (MSD-SLA) is developed such that the pipe-soil resistance force can be successfully transferred from the slice solver to the pipe element for the structural buckling analysis. A convergence study on the slice number is given, showing that the numerical results converge with the slice number when the relative distance between adjacent slices is smaller than a critical value. Then, the numerical results from the multi-slice model are validated with a simplified model, i.e pipe-surface friction model.
Then, the multi-slice model is applied to assess a realistic industrial case study. The localised buckling phenomena are focused such that the numerical results are validated with the measured field data. Three buckling initiation methods are adopted. The cyclic lateral buckling displacement is studied. With the increment of cycle number, the maximum and residual lateral displacements increase; with the further increment of cycle number, the maximum and residual lateral displacements converge. Meanwhile, the pipe-soil embedment continues increasing because of the accumulation of the soil softening effect. Large soil berms are formed in the buckling region, providing significant resistance forces to the pipeline to contain the buckling displacement development. With the increment of cycle number, some new potential buckling outbreak points are also formed, indicating that the numerical model having the potential to monitor the whole pipeline is important for the long-term safe operation.