Sahar Asrari - Faculty of Civil Engineering, Sahand University of Technology, Tabriz, Iran
Habib Hakimzadeh - Faculty of Civil Engineering, Sahand University of Technology, Tabriz, Iran
Nazila Kardan - Department of Civil Engineering, Azerbaijan Shahid Madani University, Tabriz, Iran

Investigating Local scour around an offshore pipeline has received most attention both experimentally and numerically in the last few years. So far, most of the studies on scour below the pipeline are related with a single pipeline. Offshore pipelines of different diameters are sometimes laid together as a bundle due to technical or economical attentions. A pipeline bundle comprises a large pipe and a few of small pipes. The pipelines in the bundle could either be in direct contact with each or be separated by small gaps. The most popular configuration of pipelines bundles consists one large pipeline with a small one installed exactly above the large one, as shown in Figure 1. It is supposed that the existence of a small pipeline and a gap between the two pipes will affect local scour below the piggyback pipelines. In this study the effects of the gap between the two pipelines in piggyback configuration on local scour profiles are investigated numerically