Soil longitudinal variation effects on seismic behavior of buried pipelines

The purpose of this study is to investigate the behavior of continuous pipeline passing through two different layers of soil with different levels of resistance under displacement time-histories of the same earthquake. The values of stress and displacement are studied for different angles between pipe and interface of soil layers. To this end, pipe and the surrounding soil are modeled using shell and solid elements, respectively, in ABAQUS Software. Stress and displacement values are calculated along the intersection and for different values of intersection angle between soil layer and pipeline and different values of Young's modulus of the soils. These evaluations indicate that, the maximum stress along the pipeline occurs at the node in certain distance before the interface in the harder soil. Moreover, with increasing the angle, the resulting displacement increases, and the value of stress increases with angles up to 30˚, beyond which angle it decreases. Also, a decrease in the ratio of Young's modulus increases the stress both before and after the interface. Significant changes are observed in displacement and stress along the pipeline with changing the pipe thickness, so that a decrease in the pipe thickness in the studied model from 20 to 15 mm (33% reduction) results in some 15% increase in the stress. Soft soil (two-layered soft soil) increases pipe displacement and response capacity in every condition.