When designing subsea pipelines, flowlines or cables to traverse shallow offshore regions with icebergs, iceberg keel interactions may be of concern. Given sufficiently low contact rates, the possibility of laying the pipe or cable on the seabed without burial may be an option. Consideration is then needed regarding possible denting, buckling, or lateral forces which can result in high axial tensions. In previous analyses of keel interactions, the ice keels have been treated as rigid, under the assumption that the ice strength is significantly higher than the soil strength. Recent studies have shown that under rapid loading, soil resistance can be significantly higher than previously considered, while conservatisms in estimates of ice strength have been reduced over time. As a result, ice-pipe-soil interactions are being reassessed as part of a study "SIIBED: Subsea Ice Interaction Barriers to Energy Development" (Ralph et al., 2023). This paper discusses background and progress on one component of that study, the development of improved ice strength inputs for an overall ice-pipe-soil finite element model (Barrett et al., 2023). The paper includes a review of relevant literature and describes the use of different finite-element (FEA) techniques to better understand relevant ice failure processes. Calibration of the models is largely based on the results of a medium-scale test program using a novel test frame, RHITA (Rapid-High-capacity-Impact-Testing-Apparatus), which was designed and built especially for the project.

Medium scale indentation tests have been conducted using a 12.75" diameter rigid pipe indenter, mounted on a purposely designed test frame (RHITA – Rapid High-capacity Impact Test Apparatus) and large laboratory made freshwater ice samples (approximately 4 m3 each). The purpose of this study is to collect ice failure data, representative of iceberg keel interactions with subsea pipelines or electrical cables laying on the seabed. Previous assessments of pipe response due to iceberg impact conservatively assumed no ice failure. As no widely accepted numerical models is available that captures prevalent ice failure mechanisms, experimental data was collected using RHITA. The data can be implemented in a coupled ice-pipe-soil FEA as a pressure or force limit to the ice. Also, the data can serve for calibration and validation of numerical models of ice fracture or ice crushing. The tests were executed at 0.2 m/s, a typical iceberg drift speed, on the Grand Banks of Newfoundland and Labrador. An ice mould was used to grow ice samples measuring 2.5x1.5x1.0 m (LxWxH). The top half of the ice sample was exposed, the bottom half confined by the mould. Global loads during the 2.0 m interaction were measured using six load cells, and tactile pressure sensors were used to measure the ice pressure distribution on the indenter. The test matrix includes variations of interaction depth, ice geometry, embedded rock material and ice temperature. The observed ice failure mechanisms ranged from localized damage near the interaction zone, to large fractures spanning the entire sample. The tactile pressure sensors showed the interface pressure distribution across the contact area, largely affected by local spalling events. Ice temperature and associated boundary conditions were found to affect the propagation of the cracks and resulting loads. This paper presents a summary of the tests executed from June 2022 to January 2023. Future works will include testing of rigid and flexible flowlines, and subsea electrical cable samples.