Experiment study on the local rock dumping methods for submarine pipeline spans

Unsupported phenomena occurs on submarine pipelines at different degrees due to the instability of seabed. In order to solve this problem, an integral rock dumpling method is mostly used all over the world, but its expense is quite high. In reference to domestic and foreign rock stack design experience and rock dumping engineering cases, a local rock dumping concept was newly proposed to solve the problem of submarine pipeline spans by combining with the uniqueness of rock dumping methods. Based on this new concept, it is usually to dump rocks in the middle of unsupported parts of submarine pipelines, and a single-point support is formed between the pipeline and the rock stack. In this way, the span is shortened, so the unsupported phenomena of pipelines are handled. In this paper, a case study was conducted on an in-service submarine pipeline. Based on Froude number equality principle, the break mechanism of fluids on rock stacks, the weak positions of each rock stack and ultimate anti-flow velocity of rock stacks were obtained by means of indoor tests which were designed by a scale method. And analysis was performed on the included angle between pipelines and currents, the span height, the particle sizes of external and internal rocks, and the influencing laws of the stoss side slope ratio and side-flow slope ratio on rock stack stability. It provides experimental basis for solving the unsupported issues of submarine pipelines using the local rock dumping method.