Elastic anisotropy, permeability, and freeze-thaw cycling of rapakivi granite

Abstract

Due to the ice-water transition, frost weathering in cold regions has always been in focus as a rock deterioration mechanism. Internal stresses, developed by this process, conduce to progressive fracturing and consequent changes in rock properties, particularly, elastic velocities. Previous research was mainly focused on isotropic properties of rocks. However, we have found that elastic anisotropy is substantially enhanced by frost weathering. A series of freeze-thaw tests were performed on weathered rapakivi granite fully saturated by water. The experimental basis involved: a neutron diffraction study of texture, measurements of the 3D distributions of ultrasonic P-wave velocities, and permeability at atmospheric and high confining pressures. Experimental data, along with texture-based effective media modeling of rock elastic properties, revealed the anisotropic response of elastic velocities to freeze-thaw cycling, which is related to the volume increase of specifically oriented cracks. Through permeability measurements, these oriented cracks were determined to be hydraulically interconnected and also responsible for observed frost weathering deterioration. Both ultrasonic and permeability experiments suggested a decrease in the crack closing pressure due to freeze thaw cycling.