The influence of ice rubble on sea ice friction

• Main Author: Scourfield, Sally Jane
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UCL (University College London) 2019
• Subjects: Arctic; Svalbard; Sea ice
• Online Access: https://discovery.ucl.ac.uk/id/eprint/10081261/1/Scourfield__Thesis.pdf; https://discovery.ucl.ac.uk/id/eprint/10081261/

A thorough understanding of sea ice friction is important when considering the overall dynamics of Arctic sea ice cover, since friction is the main energy sink at pressure ridges (geophysical-scale shear zones) which extend through it. It is also required for the safe implementation of various Arctic engineering activities and compliance codes, where interaction between sea ice and arti cial structures is unavoidable. Deformation of the ice cover in these scenarios often produces ice rubble at the sliding interfaces. This thesis presents an investigation into the nature of sliding of sea ice against sea ice, where ice rubble gouge separates the sliding surfaces. Particular emphasis is placed on exploring the rate dependence and memory e ects of friction, and within this the e ects of rubble gouge angularity are explored. To this end, a series of double direct shear experiments were conducted: on the metre scale during eld experiments in Svalbard and in the ice tank at the Hamburg Ship Model Basin (HSVA); and on the centimetre scale in UCL Ice Physics Laboratory. Velocity-stepped experiments were performed between 10 4 and 10 1 ms 1, which are comparable to slip velocities in Arctic sea ice cover. Slide-hold-slide (SHS) experiments were performed where hold times ranged from 1 second to 18 hours. The experimental results are discussed and compared with similar studies of sea ice sliding in direct contact. The results of SHS tests fall into two regimes - before and after hold times of approximately 104 seconds. In the rst regime the increase in friction is linear but minimal; but in the second regime strengthening increases rapidly, which is attributed to consolidation of rubble and water in the gouge region. A rate-and-state model with two state variables is developed to describe this behaviour. In addition, the velocity dependence of friction in eld and lab experiments is discussed, the di erence in sliding characteristics as a result of changing rubble angularity are described and possible mechanisms discussed; ...