Laboratory Scale Direct Shear Box Experiments on Ice Rubble: The Effect of Block to Box Size Ratio

Direct shear box experiments on rubble ice were performed in the cold laboratory of Norwegian University of Science and Technology (NTNU) in order to estimate effect of the specimen scale on the resulting mechanical properties of the material. In total 23 tests were performed, including 18 tests on dry rubble and 5 tests with having the box and the rubble submerged in saline water for 30 minutes before testing. Experiments with two ice block sizes, different gradation and two different values of confining pressures were conducted. From the shear force records measured during the experiments, values for peak friction angles and cohesion of the ice rubble were derived. In addition to these, the dilation angle of the ice rubble was estimated using the video recordings from the tests. The results from the experiments and a review on earlier experiments also presented here suggest that there is a relation between the size of the ice blocks and material properties yielded by the experiments. The results further show that the rubble dilation and the load limiting mechanism in the experiment should be carefully studied and reported in the experiments in order to gain understanding on rubble behavior.