Multiphysics Simulation and Innovative Characterization of Freezing Soils

Freezing soils are significant due to their wide occurrence in nature. A thorough understanding of their behaviors is challenged by their susceptibilities to multiphysical processes as the result of their porous nature. Further advancements in research related to freezing soils call for holistic simulation techniques and innovative instruments. This study reviewed previous research to lay down a knowledge base for investigating the behaviors of porous materials under frost action. Based on the review, it was concluded that more comprehensive multiphysics frameworks and innovative characterization techniques are highly desirable for further advancing this topic. For the purpose, a comprehensive multiphysics framework was developed by integrating and taking advantage of the knowledge base. The new model couples heat equation for heat transfer, modified Richards’ equation for fluid transfer, and mechanical constitutive relationships. Auxiliary relationships, such as the similarity between drying and freezing processes and the Clapeyron equation for phase equilibrium during phase transition, were utilized to describe the frost action. The coupled nonlinear equation system was solved under typical boundary conditions using the finite element method. To further test the performance and applicability of the model, the simulation code was implemented and verified on instrumented pavement sections and in typical buried pipe scenarios. For pavements, both flexible and rigid pavements were simulated. The simulation results were compared with instrumented data on these test pavements. For pipes, cases involving static and dynamic loads were studied, respectively. Phenomena typical of pipe-soil interactions under frost action were reproduced and several detrimental factors on the safety and durability of buried pipes under frost action were identified. On the experimental side, a new instrumentation technique, i.e., thermo-Time Domain Reflectometry (TDR) sensor, was developed to characterize the behaviors of freezing soils. The thermo-TDR combines temperature sensors and a conventional TDR module. The TDR module and algorithm measured the bulk free water content of soils during the freezing/thawing process, while the built-in thermocouples measured the variation of the internal temperature. The Soil Water Characteristic Curve (SWCC) was obtained from the simultaneously measured TDR and temperature data. The new characterization technique was verified by the filter paper method (ASTM D5298).