Doctor of Philosophy
Civil and Environmental Engineering
M. Hesham El Naggar
Permafrost in Canada’s North covers the terrain either continuously or discontinuously. Geological hazards associated with the presence of permafrost are serious barriers against development of the northern hydrocarbon resources. In recent decades, negative effects of geohazards such as frost heave, thaw settlement, slope instability on the safety of northern pipelines are widely studied; however, those of the seismic events are not. During earthquakes, buried pipelines may suffer damage from the induced transient ground deformations (TGD) and/or permanent ground deformations (PGD). While the former is caused by seismic wave propagation, the latter can result from liquefaction, faulting and landslides. This thesis investigates the effects of seismic hazards on the safety of northern pipelines.
In discontinuous permafrost regions, the subsurface conditions are complex due to the presence of intermittent scattered frozen areas. Therefore, this case is studied by means of shaking table tests and 2D numerical modelling. It is concluded that the site response at the top of frozen zones is larger than that at the top of unfrozen zones. Consequently, the pipelines in discontinuous permafrost regions are exposed to intermittent differential ground motions during wave propagation. Pipeline response to this type of excitation is investigated using a finite element program developed in Matlab in which soil and pipe nonlinearities, large deformations and cross-sectional ovalization of the pipe are considered. Tensile rupture, local buckling and premature cross-sectional failure are checked and it is observed that the pipes have a margin of safety under TGD.
Northern pipelines behaviour subjected to the PGD caused by active-layer detachments, the most common type of landslides in the permafrost regions, is also studied. Considering soil and slope uncertainties and utilizing Monte Carlo technique, probabilistic slope stability analysis is performed first. The probability of exposure to the landslide-caused PGD and the statistical distribution of the PGD zone affecting to the pipelines are computed. The pipeline response to this PGD zone is then calculated utilizing the developed structural analysis program. Finally, effects of PGD zone geometric uncertainties are simulated using Monte Carlo technique and damage functions for the pipelines under PGD are derived.
Dadfar, Behrang, "Seismic Vulnerability of Buried Energy Pipelines in Northern Canada" (2016). Electronic Thesis and Dissertation Repository. 3805.