The growth of ice in porous rocks can generate large internal pressures and progressive crack growth. The resulting damage to rock is widely believed to arise from the 9% volumetric expansion of pore water during freezing. This belief is, in fact, at odds with much of the work on freezing of soils and porous solids; under natural conditions, freezing-induced damage in these solids is strongly related to water movement and often largely independent of the specific-volume change of the pore fluid during freezing (Walder & Hallet 1986; Hallet 2006). Herein, we outline the underlying processes, and highlight recent developments to provide an introduction to this rich subject.
The potential of the 9% water-to-ice expansion to cause high pressure in confined spaces is undeniable based on practical experience with, for example, broken bottles in freezers and broken pipes exposed to freezing weather, etc. This expansion may, however, rarely be significant for rocks under natural conditions, because it requires a tight orchestration of unusual conditions. Unless the rocks are essentially saturated with water (unlikely for many situations at the ground surface; Fig. 1 for instance) and frozen from all sides, the expansion can simply be accommodated by the flow of water into empty pores, or out of the rock through its unfrozen sides.
The common notion that incipient cracks at the surface of rocks can be wedged open by freezing (as sketched in a number of textbooks) may also be rarely important in nature, because water can leak out of the cracks, and the ice capping the cracks can push out (Davidson & Nye 1985).
Ice growth inside porous rocks has much in common with frost heave of soils, which has received considerable research attention. Less well known is that slow ice growth in soils hydraulically connected to an unpressurized water reservoir over long periods, hundreds of hours, can lead to pressures against a confining piston in a stiff apparatus exceeding 18 MPa (Radd & Oertle 1973). This is far in excess of the internal pressure required for crack propagation in most rocks. Such ice growth (known as segregation ice) is sustained by a supply of water driven thermodynamically along unfrozen films toward growing ice lenses (Taber 1929). Intermolecular forces acting between the mineral surfaces, ice, and water sustain these unfrozen films, and generate significant pressure between mineral and ice surfaces (Dash et al. 2006).
