Monitoring the Soil Freeze-Thaw Process Using Piezoceramic-Based Smart Aggregate

Monitoring the soil freeze-thaw process is of great importance to engineering design of infrastructure, observation of hydrology, variation of climate, and existence of vegetation in cold regions. This paper presents experimental results to describe the soil freeze-thaw process using piezoceramic-based smart aggregate (SA) transducers. Two SAs are embedded in predetermined locations: one is used as the actuator and the other is used as a sensor. The active-sensing method is applied to excite a stress wave propagating between the two SAs. The alteration of the mechanical properties of the soil during the freeze-thaw process has an important effect on the stress-wave propagation, and the transition between the freeze and thaw states of the soil is monitored in real time. A wavelet packet-based soil freeze-thaw status indicator is established to quantitatively describe the soil status during the freeze-thaw process. Potentially, this freeze-thaw status indicator can be linked to soil mechanical properties, and therefore the methodology presented here can be used to characterize a partially frozen soil or warm permafrost site.