Offshore Arctic pipelines must be designed to withstand unique loading conditions of seafloor gouging by drifting sea ice ridge keels and icebergs. Due to the high cost of offshore pipeline burial, determination of the required burial depth is a critical factor for economical designs. One of the components of burial depth is the distance the top-of-pipe must be placed below the design gouge depth to protect it from excessive stress/strain due to subgouge soil deformation. While industry has done much over the past two decades to understand the complex ice/soil/pipe interaction process, there remains considerable uncertainty in our ability to estimate pipe strain due to soil displacement below a gouging ice feature. This paper presents an advanced 3D continuum model for estimating strain demand as a possible alternative to the currently accepted methodology based on published empirical equations for subgouge deformation and pipe-soil spring models. Some of the important numerical simulation techniques employed include Eulerian mesh for the soil to model extreme material deformation, complex soil material models with material parameters determined from standard triaxial test data, and optimum mesh density in the pipe-soil contact region. These advanced models, which capture the ice gouging physics and coupled soil-pipe interaction more accurately, generally predict lower subgouge soil deformations and pipeline burial depths compared to the current industry methodology. Since the greater accuracy comes with a significant increase in computational intensity, guidance is provided for the practical implementation of such advanced models in the design process. The authors believe that advanced continuum models, once properly validated using centrifuge and large-scale field tests, can be used to determine reliable and potentially more economical pipeline burial depths.
Offshore arctic regions may contain several types of ice features that are capable of scouring the sea floor, including icebergs, first year ice ridge keels, and multiyear ridge keels. The ice features are continuously moving under the action of environmental forces (e.g. wind and ocean currents) and, whenever their draft is larger than the local water depth, they scour the seabed producing the characteristic process of ice gouging. Figure 1 shows a schematic illustration of the ice-gouging process.