Samcot_annual_report

Annual Report 2016

SAMCoT

SEA ICE MECHANICS

Mark Shortt is a first-year SAMCoT PhD candidate

working at the Institute for Risk and Disaster Reduction

(IRDR) at the University College London (UCL). Shortt’s

basic area of study is sea ice mechanics. When two flo-

es of sea ice directly collide, two possible deformation

mechanisms can occur. The first is rafting, which is the

overriding of one ice sheet by the other. The second is

ridging, which is the breaking up of the ice sheets into

an elongated pile of rubble. Both scenarios generally

comprise the same basic situation; pieces of ice sepa-

rated by a (relatively) thin liquid layer of seawater. Over

time, the liquid layer freezes and the ice pieces gradual-

ly bond to form a coherent sea ice feature. This process

of freezing and strengthening is known as consolidation.

This is important as the degree of consolidation governs

the strength of the ice feature.

Shortt’s main research interest is investigating how the

strength of thick sea ice features (ridging and rafting)

changes as a function of the degree of mechanical

consolidation. He will also be assessing the risk posed

by these consolidated ice features to offshore structures

in the Arctic. Shortt’s research comprises both experi-

mental work and mathematical modelling, and will also

be supplemented by work in the field. He will devise a

micromechanical model of freeze bond failure between

layers of saline ice, which will be experimentally

tested using UCL’s Scanning Electron Microscope (SEM)

facilities. Microscopic mechanical deformation tests

(compressive, tensile and 3-point bending) on freeze

bonds will be conducted using the Deben Microtest rig,

and freeze-bond failure will be simultaneously imaged

under the SEM.

For the model to be applied to the real world it must

be scaled up from the micro-scale to dimensions found

in nature. To investigate the effect of spatial scaling,

mechanical tests on freeze bonds will be performed on

the laboratory (centimetre) and field (metre) scales.

Mechanical tests on the intermediate scale can be

undertaken using the confined biaxial cell, which

subjects ice samples to a true triaxial stress at strain

rates between 10

-4

and 10

-8

-1

and at temperatures

down to -40

Shortt conducted a review of the literature, which has

helped to develop his knowledge of ice mechanics. He

has learned how to grow and prepare saline ice using

the facilities available in UCL’s Ice Physics Laboratory

and has assisted with mechanical tests on ice rubble

using the uniaxial deformation cell.

Image of the confined biaxial cell

situated in the UCL cold rooms