ABSTRACT: The process of self-burial of pipelines at span shoulders has been investigated experimentally in the laboratory in steady currents. Only the non-cohesive sediment bed is considered. A rigid cylinder has been used as the pipe model. In all the tests, the experimental conditions were arranged such that the pipe is supported by a sand ridge in the middle. When the" length of this supporting ridge is decreased to a critical value, the pipe begins to sink in the sand due to soil failure. The scour, the sinking and, at a later stage, the backfilling processes were monitored by video in plan and side views simultaneously. A simple formula adopted from soil mechanics regarding the bearing capacity of soil was found to give a satisfactory result in relation to the sinking of the pipe at the span shoulder.
INTRODUCTION It is known that pipelines laid on the seabed may bury themselves. The self-burial of pipelines occurs both in the free-span areas and at span shoulders. In the former, when the scour hole below the pipe is sufficiently long the pipe begins to sag in the scour hole. By the time when the pipe reaches the bottom of the scour hole, the scour stops and the back-filling process starts, and subsequently the pipeline may be covered by sand and presumably be self-buried. This type of self-burial process has been investigated fairly extensively in the past (Leeuwestein et al. (1985), Freds0e et al. (1988) and Gokce and Gunbak (1991)). Regarding the second type of self-burial of pipelines, namely the self-burial at span shoulders, the development of this process is closely related to the three-dimensional scour which occurs underneath the pipe in the area where the free span joins the span shoulder.