The behaviour of artificially frozen ground is largely dependent on its temperature-dependent thermal and hydraulic properties. The existing ratio of ice to unfrozen water has to be correctly represented for a realistic ascertainment of this behaviour and thus a forecast of the freezing time during icing work. The phase change model presented here can be used to describe the unfrozen water content and thus the freezing behaviour as a function of the temperature. Optimisation possibilities can then be investigated on this basis in the run-up to icing measures.