Understanding ice rubble strength and associated failure mechanics is important for a variety of engineering applications in marine ice environments, including the design and operation of coastal, offshore, subsea and floating structures. As part of the Mechanics of Ice Rubble project, recent experiments have been carried out to study the strength and failure behavior of ice rubble beams and the freeze bonds that form between individual ice blocks. These new results serve as an important guide for the development of improved numerical models. The discrete element method (DEM) is a direct modeling approach which has the potential to both describe and enhance understanding of the behavior of brittle granular materials, especially with regard to the evolution of damage towards failure. In this study we present results obtained from a newly developed model for the 3D DEM open-source code LIGGGHTS. The ice model contains normal and shear springs that operate between neighboring particles which are bonded or that overlap due to compressional stresses. Energy dissipation is accounted for by using a viscous damping model. Using this DEM model, medium-scale freshwater ice rubble punch tests have been simulated for ice rubble beams with nominal dimensions of 0.50m × 0.94m × 3.05m. Rubble specimens were generated by “raining” individual DEM ice pieces into a rectangular form and compacting the rubble mass to achieve the target porosity. Before the compacting pressure was removed, bonds between contacting blocks were introduced with parameter values chosen based on representative freeze bond experiments. The ice rubble beam was then deformed by pushing a platen vertically downward through the center of the beam until failure occurred. For the numerical simulations presented here, two types of block size and shapes have been considered: cuboid blocks generated based on the size distribution of the actual rubble, and rubble blocks generated by image processing of actual blocks of broken ice used in the comparison experiments. Results obtained for these two scenarios are compared with corresponding experimental test data. These results highlight that the DEM model is useful for estimating the flexural strength of the rubble, simulating the failure mechanism and for examining the extent to which the ice rubble beam failure is controlled by the strength of the freeze bonds. These results also provide valuable new insights regarding the importance of shape and size distribution of ice blocks on simulated ice rubble strength and failure behavior. Recommendations for future work are provided.

A three-dimensional discrete element model is under development to simulate a number of different keel-gouge and subsea interaction scenarios. The model is being validated against controlled tests conducted in the National Research Council’s ice tank facility under the Pipeline Ice Risk and Mitigation (PIRAM) Joint Industry Project, which was led by C-CORE on behalf of a number of oil and gas companies. To investigate the influence of certain key parameters on the failure behaviour of the keel, a sensitivity analysis has been carried out. Best results were achieved when Young’s modulus of the keel was 5 MPa, the shear-to-tensile ratio of the freeze bonds was set to 1.2, the internal friction angle of the ice was 9°, the bond breakage ratio 0.8 % and Young’s modulus of the gravel 0.01 MPa. A low modulus for the gravel was needed to prevent premature failure of the keel, a consequence of the model not accounting for soil deformations. Using these parameters the model was able to accurately reproduce the loads on the soil tray during peak loading. Future developments in the model include using ‘clumps’ to give more representative ice block shapes, which will allow interlocking between ice pieces and the development of force chains.

In coastal regions throughout the Arctic, the seabed is frequently scoured or gouged by sea ice ridges and icebergs. This presents an environmental hazard to pipelines or subsea infrastructures operating in the area and therefore a greater understanding of these processes is needed. This paper describes a three dimensional (3D), numerical model that was developed to simulate the failure behavior of a ridge keel as it interacts with the seabed. The simulation was conducted in Yade, an open-source code, which uses the Discrete Element Method (DEM) to model particle motions. The ice blocks in the ridge keel are modeled as spheres, which are initially bonded to contacting blocks via freeze-bonds. A Cohesive Frictional Model (CFM) which has cohesive bonds in tension and shear was used to simulate the freeze-bonds between ice blocks. In addition to normal and shear bonds, the model features springs which resist compression, shear, bending and torsion. Once the bonds are broken the material is assumed to behave like a Mohr-Coulomb material with a constant friction angle. Since the main focus of this paper is the failure behavior of the keel, the seabed is simplified as being rigid. Numerical simulation is compared with data collected from the Pipeline Ice risk Assessment and Mitigation (PIRAM) test program.

Shipping operations along the coasts of Newfoundland and Labrador associated with Grand Banks oil and gas production, as well as mining operations in Labrador, may be exposed to potentially hazardous ice conditions. Possible future development of oil and gas reserves offshore Labrador will also be exposed to risk associated with iceberg and pack ice conditions. Improved understanding of the characteristics of ice dynamics and metocean forcing mechanisms behind them will lead to more efficient operational planning and safer operations. Accordingly, CARD has initiated a long-term project to collect and analyze data on the pack ice and iceberg dynamics in these regions. This paper presents an analysis of the drift of pack ice features and two icebergs tagged with satellite-tracked buoys during April-August and July-August 2014, and characterizes their drift in the context of the winds and currents driving their dynamics.