Properties of elastic waves in sand-silt mixtures due to freezing

The freezing of soil converts a particulate medium into a continuous solid bonded by ice bridging. The objective of this study is to investigate the property changes in elastic waves, including shear and compressional waves, in a sand-silt mixture during soil freezing, using bender elements and piezo disk elements. Experiments are performed in a small freezing cell, which is designed to freeze soil specimens from top to bottom. Bender elements and piezo disk elements are used for the generation and detection of the shear and compressional waves. Two pairs of bender elements and two pairs of piezo disk elements are installed in the walls of the freezing cell at two different depths. A sand-silt mixture, with a silt fraction of 10% and a degree of saturation of 40%, is frozen in a freezer. As the temperature of a specimen drops from 20°C to -10°C, the velocities, resonant frequencies, and amplitudes of shear and compressional waves are continuously monitored. Experimental results show that the properties of the elastic waves change markedly as the specimen is freezing; the velocities of the shear and compressional waves dramatically increase. Poisson's ratio continuously decreases with the decrease in temperature, and becomes constant after soil freezing. In addition, huge increases are observed in the resonant frequencies of both elastic waves. This study demonstrates that the dramatic increases in both velocity and resonant frequency result from the ice bonding of the particulate mixture as a result of freezing of the pore moisture.