Weathering by segregation ice growth in microcracks at sustained subzero temperatures: Verification from an experimental study using acoustic emissions

TLDR

The segregation‑ice‑growth model offers alternative insights into frost weathering and calls for a more unified understanding of related geomorphic processes. The authors aim to test the theoretical model of crack propagation driven by segregation ice growth in water‑saturated rocks and to evaluate lithological influences. They froze a rectangular Berea sandstone block unidirectionally under a fixed temperature gradient while continuously monitoring and locating acoustic emissions to track microfracture propagation. Experiments showed that ice growth in an open system causes substantial frost damage, with microfracturing occurring at temperatures between –3 °C and –6 °C—well below the freezing point—and without requiring freeze–thaw cycles, confirming the model’s predictions.

Abstract

Abstract In a continuing effort to better understand the frost‐induced breakdown of rock, experiments were designed specifically to assess a theoretical model of crack propagation due to segregation ice growth in water‐saturated rocks with interconnected cracks (Walder and Hallet, 1985). A rectangular block of Berea Sandstone was frozen unidirectionally while the temperature and acoustic emissions, which reflect microfracture propagation events, were monitored. Acoustic emissions were counted and approximately located as a function of time and temperature while the rock sample was subjected to a fixed temperature gradient. The experimental results indicate considerable frost damage to sandstone due to ice growth in an open system with migration of water to freezing centres much as segregation ice grows in soils, as has been previously suggested. Freezing‐induced microfracture propagation events are not associated with the freezing temperature, which is about —0.2 ºC for Berea Sandstone; most of the fracture activity occurs at distinctly lower temperatures, between —3 ºC and —6 ºC, in accord with our theoretical predictions. Such microfracturing does not require freeze‐thaw cycling or even falling temperatures; temperatures were held constant but spatially nonuniform for the duration of most experiments. Through a series of experiments other aspects of the model are being tested and the influence of lithology is being examined. Diverse geomorphic implications of this model are discussed because it offers attractive alternative insights to those available with the conventional view of frost weathering. A plea is made to strive towards a more fundamental and unified view of frost weathering and related phenomena.