Sea Ice Scour Depth and Width Parameters for Design of Pipelines in the Caspian Sea

摘要

Wind stresses on sea ice in the north-eastern Caspian Sea during winter result in the formation and movement of ice ridges and grounded ice structures called stamukhi, with resulting scouring and pitting of the seabed. In designing subsea pipelines, consideration needs to be given to associated loads on the pipe. This paper describes methods that were developed to estimate the expected maximum width and depth of scours at specified annual probabilities of exceedance per kilometre of pipe. These parameters were subsequently used with ice-soil-pipe interaction models to ensure pipeline designs and burial depths met required reliability levels. Available data consisted of multi-beam echo sounder imagery of scour crossings along planned survey lines. Additional images of scour crossings as well as complete scours were obtained from targeted surveys in which operators followed scours or surveyed areas believed to have relatively high probabilities of deep scours. While the general distribution of soil types for the survey region was known; insufficient soil properties were measured at each scour for direct correlation to scour depth and width. The paper describes the methods used to determine appropriate scour width and depth parameters for design given the sources of uncertainty in the data and uncertainties regarding processes and ice features resulting in scour formation. This includes selection and fitting of distributions, accounting for differences between unbiased and biased survey data, and calibration and application of models.