A novel method to monitor soft soil strength development in artificial ground freezing projects based on electromechanical impedance technique: Theoretical modeling and experimental validation

The artificial ground freezing is an important technique for soft soil reinforcement and underground water sealing carried out by continuously refrigerating ground. It is of great significance to monitor the soil strength development in artificial ground freezing projects not only for better evaluation of the soil freeze-thaw status but also for predicting and controlling the concurrent adverse effects which may cause serious engineering accidents. In this study, the electromechanical impedance method was explored in monitoring the soil strength development in the freeze-thaw process. The lead zirconate titanate transducer was embedded inside the soil specimen, and changes in the conductance signatures were monitored throughout the soil freeze-thaw process. The experimental results indicate that the resonant frequency of the embedded lead zirconate titanate transducer can serve as a reliable index for assessment of the soil's dynamic elastic modulus in the freeze-thaw process. More importantly, an analytical model was developed based on the piezo-elasticity theory to characterize the correlation between the electromechanical impedance of the lead zirconate titanate transducer and the soil's mechanical properties, and its validity was further confirmed by the experimental research. Based on the proposed model, the development of the soil's strength can be well predicted from the measured conductance signatures. As a nondestructive testing method, the proposed soil testing technique will help save considerable time and resources by avoiding the conventional sampling, specimen preparation, and testing of soil. The theoretical and experimental research will contribute to the future application of the electromechanical impedance method in real-life artificial ground freezing engineering projects.