Strength and failure mechanisms in scalemodel ridge keel punch through tests: Feanalysis

This paper analyses scale-model ridge keel punch through tests and dry oedometer tests performed in HSVA to investigate the strength and the failure mechanisms in model-scale ice rubble. Numerical continuum based finite element model was applied with the shear-cap failure criterion. Both Coupled Eulerian-Lagrangian (CEL) framework and conventional explicit simulation based on Lagrangian framework were utilized for the numerical simulations. The main parameters in the shear-cap model to describe the shearing failure are cohesion and friction angle and the post failure behaviour is modelled by the cohesive softening. Compaction of rubble is determined by the cap hardening behaviour. The oedometer tests (Serré et al., 2009) were made in dry conditions. A cylindrical container was first filled by ice rubble taken from the model ridge and thereafter immediately compacted by the uniaxial load. The load-displacement relationship was then used to evaluate cap-hardening curve. In the punch test (Serré et al., 2009) a circular cut was made through the consolidated layer along the perimeter of the platen. During testing the platen was lowered through the keel until certain submersion. The punch test simulations resulted in fairly similar load-displacement curves as measured in the tests. A large area of rubble was compacted underneath the loading plate in all simulations for all values of cohesion and friction angle. Despite the compaction, the shear failure zone progressed from the edge of the platen downwards through the keel. By comparing simulations of the model-scale results to previous simulations of in-situ results, the two main conclusions are that the compaction of rubble seems to be more prominent in the model scale due soft ice particles and that in-situ ridges have substantially higher cohesion (10-25 times). The compaction may have an important influence on the failure mode of ridge, so that the failure mode in small-scale ridge-structure interaction may differ from the fullscale even if the strength may be appropriately scaled