Changes in the external geometry of the pipeline laid on the erodible beds may affect the local scour around pipe. If the scouring process below the pipe is accelerated, the pipe buries on the bed (known as self-burial of the pipe) and can be used as a cheap alternative to mechanical trench digging. In this study, the effect of changes in the external geometry of the pipe in order to accelerate the scouring and self-burial pipe processes by spoiler and piggy back under unidirectional flow on the erodible bed is investigated. The results showed that the time scale of self-burial process is less than that of the scouring process. At the angles of 180, 135 and 225°, the Spoiler and piggy back reduced the time scale of self-burial and scouring process and increased the scour and self-burial depths, as well as the lee erosion length as compared with the simple pipe. At angles of 90 and 270°, the scale time of scour and self-burial processes are increased, the scour and self-burial depths and the lee erosion length are decreased as compared with the simple pipe. It can be concluded that the performance of piggy back is similar to the spoiler, therefore, they are of similar application and could be a suitable alternative for the spoiler

Keywords