Seismic Ground Displacement and Pipeline Design Evaluation—A Case Study

The limit equilibrium method for evaluating the slope stability only provides a factor of safety against slope failure and offers no insight into the magnitude and distribution of the ground movement. An alternative approach is to design the pipeline to accommodate the anticipated ground displacement. This approach relies on the development of two numerical models. The first model, a 2D, dynamic, and effective stress FLAC model of the slope to estimate the magnitude and distribution of the seismically induced ground deformation. The second model, a 3D pipe-soil interaction finite element model, is used to evaluate the tensile and compressive strain in the pipeline. This paper presents a case study of the use of this approach to design a drinking water pipeline crossing of Beaverton Creek where up to approximately 3 m of seismically induced permanent ground deformation is estimated, resulting from soil liquefaction. The NPS 48, steel, and butt-welded pipeline will be installed via open cut and two trenchless drives. Based on the results of the paired analyses, pipe wall thickness was increased in areas with high strain. The use of expensive and time-consuming ground improvement was deemed unnecessary.