Mechanics of dynamic ice failure against vertical structures

Ice interaction with vertical faces of structures can result in regular vibrations given certain conditions such as temperature and speed of interaction. The mechanism that can provide this regular behaviour is studied. Fracture in general does not offer a solution in compressive failure. An approach based on viscoelastic theory, with softening resulting from microstructural change, is given. The pivotal observation was a layer of microstructurally modified ice adjacent to the structure or indentor, together with high local pressures transmitted into the layer. The microstructural changes include microfracturing and recrystallization. A series of triaxial tests was performed to determine the inputs into the viscoelastic theory. The theory recognizes changes in the microstructure of the ice by means of a state variable, which is a function of prior stress history, and therefore of location within the ice mass. The theory and the calibration thereof are reviewed, and the results of triaxial tests examined. One feature of these tests is the occurrence of \u201crunaway\u201d strains and associated localization of damage. This appears to be sensitive to confining pressure, and is considered to be a key factor in the rapid load drops observed in ice-structure interaction. Temperature effects are also studied. Directions for future research are identified.Peer reviewed: YesNRC publication: N