Monitoring the freeze-thaw process of soil with different moisture contents using piezoceramic transducers

Water content plays an active and important role in the performance of the soil freeze-thaw cycle to form frozen soil mechanical properties. Monitoring the freeze-thaw cycle of soil with various types of soil with varied moisture content will provide a direct observation of the properties of soil in cold regions. This paper presents new findings from monitoring the freeze-thaw process of soil using a piezoceramic-based smart aggregate (SA). For comparison, clay soil and medium sand with different moisture contents were used to study the behavior of the soil under the freeze-thaw process. Two SAs were embedded in the soil specimens with a pre-determined distance between them, one as an actuator to generate a stress wave and the other as a sensor to detect the propagated wave. As the propagation of the emitted wave is sensitive to soil status and properties, it is possible to monitor the soil freeze-thaw process by interpreting the SA sensor signal. Based on the attenuation of the energy, a freeze-thaw status indicator was established to describe the freezing-thawing condition. Indicator values of soil specimens with different types and different levels of moisture in freeze-thaw cycles were studied. The test results indicate that the freezing duration in the freezing-thawing process varied for different types of soil and different initial moisture content of the soil. Soil with different particle sizes and moisture content will determine the frozen soil microstructure and its corresponding mechanical properties. Our results illustrate that if soil particle size is bigger, then the signal indicator is stronger; if the moisture content is higher for the same soil, then the signal indicator is stronger. The research presents an innovative method to investigate the freezing-thawing performance of soil and potentially points to a new method to study the variation of soil mechanical properties during the freezing-thawing process, which is a critical problem for infrastructure in cold regions.