Susceptibility to frost wedging is influenced by rock properties and environmental parameters governing stress intensity at crack tips. The ice pressure causing frost wedging arises from expansion of water upon freezing, or from the adsorptive force that draws water into the interface between ice and rock. Ice pressure is an order of magnitude higher when ice and water pressures remain equal during freezing (confined water) than when free water remains at atmospheric pressure (unconfined water) and adsorptive force conditions prevail. Capillarity generally does not produce stresses of sufficient magnitude to propagate cracks.
Two distinct crack geometries are analyzed. In coarse-grained porous sedimentary rock, the diameter of pores dictates effective crack aperture and a crack with effectively constant aperture (rectangular crack) results. In other rocks, the aperture of cracks diminishes gradually toward the crack tip (tapered crack).
Rectangular cracks more than ∼1 mm long will propagate for short-term confined-water conditions, or with stress corrosion, for long-term unconfined-water conditions. The tapered cracks of crystalline rock must be 14 cm long to propagate under short-term confined-water freezing and 1.4 cm long for long-term loading with unconfined-water conditions. Tapered cracks an order of magnitude shorter will propagate with unconfined water if they are connected to a reservoir of unfrozen water, allowing adsorptive force suction.
Cracks with aspect ratio (maximum aperture/crack length) greater than 0.01 and terminating in sharp crack tips are most susceptible to frost wedging, because ice expansion in these wide cracks causes sufficient dilation to produce critical stress intensity at the crack tip. Some relaxation of ice pressure by plastic flow is expected in wide cracks, but its effect is small.
- Geological Society of America