| The thesis is dedicated to the understanding and characterization of brittle compressive fracture of columnar S2 ice. The work quantifies the strength of fresh-water S2 ice and investigates its characteristic brittle failure modes under biaxial proportional across-column loading. All experiments were conducted at −10° ± 0.2°C on sets of microsimilar plate specimens. The load was applied biaxially, perpendicular to the axis of the columns. The minor compressive stress was proportional at all times to the major compressive stress by a pre-set fraction R, termed confinement ratio, which varied between 0.0 and 1.0. In the first stage, the brittle compressive failure envelope of fresh-water S2 ice under biaxial compression was constructed. The failure envelope is convex about the origin and exhibits an ascending branch followed by a descending one. The ascending branch represents clear evidence in support of the Coulombic character of S2 ice. Six distinct faulting patterns were observed. In the direction of increasing confinement ratio these faulting patterns are: axial splitting, shear faulting, shear faulting with in-plane cracking, spalling, spalling accompanied by horizontal faulting, and spalling accompanied by shear faults inclined at 25°–30° with respect to the direction of the pre-set minor compressive axis. Associated with these faulting patterns are the three fundamental brittle failure modes of S2 ice under across-column compression (axial splitting, shear faulting, and spalling) and three shear faulting and/or spalling-based variations or combinations. Two new wing-crack based failure mechanisms are proposed for shear faulting and spalling brittle failure modes. In the case of shear faulting, the orientation of faults is strongly influenced by the type of end conditions applied. Following the initial findings of Gupta et al. (1998), the work investigates the conditions under which step-loading (incremental loading) increases the brittle compressive strength of fresh-water S2 ice and quantifies the magnitude of the increase as a function of the applied average stress increment. It is also demonstrated that step-loading does not change the overall brittle failure mode compared to monotonic loading. |
