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.
Ferroelectric-dielectric composite materials are attractive for a range of applications in future functional devices. Here, we utilized a free energy based computational approach to investigate the electric-field driven response of isolated ferroelectric nanoparticles embedded in a dielectric matrix and its dependence on particle size, shape, and orientation of the applied field E. Particle shapes belonging to the superellipsoidal family were considered, including octahedral, spherical, and cuboidal structures, as well as a number of intermediate geometries. Perovskite PbTiO3 and SrTiO3, respectively, were chosen as the prototypical ferroelectric and dielectric materials. In particles of all shapes that are large enough to support domain walls at zero applied field, we observed polarization switching by a formation of intermediate phases, which possess an appreciable amount of vorticity stemming from the domain wall motion through the ferroelectric inclusion volume. The system coercive field Ec and energy storage efficiency were found to be strongly dependent on the particle shape and the orientation, but not on its size. In near spherical particles with easy polarization axis pointing away from the direction of E, smallest Ec and highest storage efficiencies were obtained, while nonspherical particles with aligned easy polarization and E directions exhibited highest Ec and relatively low energy storage efficiencies.
The field evaluation of pile-soil combination is a key step in the service life evaluation of pile foundation. However, due to the time-varying nature of pile-soil interaction, there is no efficient method to accurately analyze it. This paper introduces a health monitoring technique for assessing the state of pile-soil bond. The transient vibration of pile-soil coupling was measured by piezoelectric ceramic sensor. In the experiment, the different bond states of pile and soil were simulated by taking clay of different density as an example. A horizontal force is applied to the top of the pile, and the induced stress wave is detected by piezoelectric ceramic intelligent aggregate sensor embedded in the pile. At the same time, taking the artificial separation of pile-soil as an example, the binding state of pile-soil is analyzed, and the influence of different soil conditions on the pile-soil bonding characteristics is studied. An energy index for quantitative evaluation of pile-soil binding quality is proposed. Taking piles buried in two layers of soil with different densities as an example, the effects of soil with different densities on pile-soil bonding characteristics were studied. Experimental and numerical results verified the effectiveness of the proposed method. The three factors influenced the pile-soil coupling. The experimental and numerical results verified the effectiveness of the proposed approach and pave the way for an approach to directly judge whether there is separation between the pile and soil and evaluate the pile safety.
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