Richard McKenna

Processes of Deformation and Fracture of Ice in Compression

The analysis of crushing of ice in compression is addressed. As background, a test result from the Pond Inlet spherical indenter experiments is presented. This shows the dramatic fluctuations in load experienced when crushing is the dominant mechanism of ice fracture. In order to analyse the degradation of strength of ice in compression, damage mechanics is used. Starting with combined Maxwell and Kelvin elements to model undamaged ice, a rate-theory approach is used to generate microcracks. Separate sets are developed, one for the Maxwell and the other for the Kelvin element. The effect of microcracks is to degrade the elastic potential of both elements and to cause an enhancement of viscous movements, taken as being stress-dependent, also for both elements. The analysis is developed in the context of thermodynamic theory and the results are compared to a set of experiments. Good agreement is obtained. Phenomena which lie outside the framework of the viscoelastic elements are discussed. These relate primarily to frictional movements across newly developed crack faces. Stick-slip movement is a possible mechanism in this regard. Sintering, which can be seen as the reverse of the damage process, is also potentially of importance. Immediately following rapid release of strain energy, kinetic effects may need to be considered.

Probabilistic Design Methodology to Mitigate Ice Gouge Hazards for Offshore Pipelines

For offshore pipelines located in ice environments, the mitigation of ice gouge hazards presents a significant technical challenge. A traditional strategy is to establish minimum burial depth requirements that meet technical and economic criteria. A probabilistic based approach to optimize burial depth requirements based on equivalent stress and compressive strain limit state criteria is presented. The basic methodology is to define ice gouge hazards on a statistical basis, to develop numerical algorithms that model ice gouge mechanisms and pipeline/soil interaction events, to define failure criteria, limit states and target reliability levels and to conduct a probabilistic assessment of pipeline burial depth requirements. Application of the probabilistic design methodology for a generic pipeline design scenario subject to ice gouge hazards is presented. Implications on pipeline design and future applied research initiatives are discussed.Copyright

Influence of Velocity on Ice-Cone Interaction

A series of upward breaking cone tests was conducted at NRC/IMD’s ice tank in level ice using EG/AD/S correct density model ice. Cone angles of 45° and 60° were tested. The effect of ice draft velocity in the range 0.005 to 0.5 m/s was studied for ice thicknesses ranging from 35 to 110 mm. The mean peak forces in both horizontal and vertical directions were measured and found to be almost independent of Froude Number below 0.02, but increased significantly at higher Froude Numbers. The effect of speed for upward breaking conditions was found to be less than similar conditions for downward breaking cones.