How does ice fracture rock?
Aylin Dursun, Physics.
Introduction Under certain conditions, large ice layers can build up in the ground. They are created due to a physical process where water in the non-frozen earth layers beneath the ice is subject to a force pulling it towards the ice. Hence, water migrates to the ice, “feeding” the ice layer. We do not yet understand how this process propagates fractures in low porosity, low permeability bedrock. The aim of the current research is to develop experimental techniques allowing us to study a model of the dynamic ice-rock interface during slow fracture propagation. Method We will develop a model where we observe crack propagation by making a “transparent rock”. By using a Plexiglas block, we can actually see and monitor the evolution of a crack propagating in a weak plane in the block. Before using frost to propagate the fracture, we will use pressurized water. By measuring the pressure we can calculate the stress intensity factor, K_I, which can be thought of as the driving force propagating the fracture. Our first goal is to determine the relationship between the fracture-front velocity and the driving force. Preliminary results We have created a liquid-filled initial crack in the weak plane, with no trapped air. When the radius is approximately 1 cm, the pressure needed for propagation is measured to be roughly 7 bars. Discussion The crack-front velocity is expected to depend on temperature. As frost-driven propagation occurs at subzero temperatures, we plan on doing measurements at different temperatures and extrapolate the results.