Path-Dependent Frost-Wedging Experiments in Fractured, Low-Permeability Granite

To investigate the mechanism of frost wedging in fractured low-porosity bedrock, we monitored the opening of an artificial 4mm wide and 80mm deep crack, cut 20mm from the end of a rectangular granite block. Two freezing protocols were employed - top-down and bottom-up, the former consisting of short- and long-term variants, lasting 1 and 53days, respectively. Our results demonstrate that (i) in 1-day experiments, maximum crack widening during top-down freezing is around 0.11mm, while bottom-up freezing produces only 0.02mm of deformation; (ii) neither ice nor water pressure causes measurable irreversible crack widening during 1-day tests; (iii) irreversible crack widening is only observed following the 53-day experiment under top-down freezing. Based on these results, we suggest (i) freezing direction plays a key role in determining the magnitude of crack widening; and (ii) freezing duration could be essential for crack propagation. The fracturing is both time-dependent and subcritical; thus, persistent freezing in winter could actually be the active period of crack propagation. This allows us to propose a simplified method to calculate ice pressure according to crack widening. Here we show how freezing direction and duration in ice-filled cracks control the path-dependent efficacy of frost-wedging. Copyright (c) 2017 John Wiley & Sons, Ltd.