Seismic Design of Buried Steel Pipelines

Earthquake hazards like seismic-induced landslides, lateral spreading due to soil liquefaction and faulting seriously threaten the safety of buried pipeline systems, highlighting the need to accurately evaluate their structural performance within the engineering design practice. In the last decades, this problem has been tackled numerically using the simplistic beam on Winkler foundation and the more complex continuum model. While the former is incapable to model the realistic soil-pipeline interaction for large deformations and to capture the pipeline local instabilities, the latter is computationally expensive and requires the operator's expertise. This thesis analyses the seismic performance of a straight buried steel pipeline subjected to strike-slip faulting within the finite element method, using the beam on Winkler foundation and the continuum approach. The effect of different soil and pipe parameters having a critical role on the pipeline response is carefully investigated, such as the fault inclination angle, the pipeline burial depth, the soil material, the pipe thickness and the internal pressure. To optimize the computational costs, each end of a limited pipe segment crossing the fault is connected to an equivalent-boundary spring, representing the interaction with the rest of the soil-pipeline system. Within the continuum model, both soil and pipe contact surfaces are meshed with a similar mesh size that guarantees solution convergence. Moreover, the introduced submodeling technique allows to focus with a finer mesh on the limited part of the model susceptible to local buckling, permitting to accurately evaluate the critical fault displacement for this performance limit state. The numerical results obtained using both models are properly compared between each other as well as with recent research literature data, giving better insight on the mechanical behaviour of the soil-pipeline system under strike-slip movement. In conclusion, a series of recommendations are proposed to enhance the seismic design of buried steel pipeline crossing active faults. The proposed modelling procedure, including the submodeling technique and the exact analytical formulation of the pipe boundaries in function of the system parameters, can be suitably used to accurately and efficiently analyse the seismic performance of buried pipelines.