TENTATIVE FRACTURE MECHANISMS OF THE PARALLEL CHANNEL EFFECT DURING ICE MANAGEMENT

摘要

During an ice management operation, parallel channels were often created by the operating icebreakers. Because of the close-by free boundary effect induced by a neighbouring parallel channel, large cracks may form linking these parallel channels. These large cracks intersect the solid ice in between and generate smaller broken ice floes. This is beneficiary for an effective ice management operation. This phenomenon has been frequently observed and recognised in various field tests and reported in scientific publications. However, up to now, there exist no theoretical explanations behind this 'parallel channel effect'. As an initial step towards addressing practical problems in relation to 'the optimum parallel channel spacing' and 'the out-going floe size' for certain ice management patterns, we present in this paper a theoretical model based on fracture mechanics to account for the repetitively observed two types of cracks, i.e., the side and front cracks. Based on both field observations and theoretical analysis, we found that this theoretical model offers reasonable predictions, In addition, different behaviour and characteristics of side and front cracks were identified, e.g., front cracks tend to kink toward the nearest free boundaries at an angle of about 50°, side cracks show a strong tendency of kinking away from the free boundary with an angle of 90°. Furthermore, for the sake of enhancing the parallel channel effect, geometrical considerations such as the requirement on the parallel channel's spacing and the aspect ratio of out-going broken ice floes were addressed in a ratio format in this paper. Further quantifications of these practical problems can be built upon such information in separate studies.