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

Abstract To investigate the mechanism of frost wedging in fractured low‐porosity bedrock, we monitored the opening of an artificial 4 mm wide and 80 mm deep crack, cut 20 mm 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 53 days, respectively. Our results demonstrate that (i) in 1‐day experiments, maximum crack widening during top‐down freezing is around 0.11 mm, while bottom‐up freezing produces only 0.02 mm 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 © 2017 John Wiley & Sons, Ltd.