A Coupled Thermal-Hydraulic-Mechanical Model for Frost Heave
Frost heaving is a major cause of damage to infrastructures structures in cold regions. While significant contributions to revealing the mechanism of frost heaving in soils began in the late 1920s, modeling efforts did not start until decades later. Several models describing the heaving process from a macro and micro perspective were developed in the past. Although it is well-established that frost heave is closely related to water migration due to suction generated during the freezing process, the most recent advance in unsaturated soil mechanics was not taken into considerations when developing such constitutive models for frost heave. None of them has been generally accepted as a tool in engineering application. The paper proposed a coupled thermal-hydraulic-mechanical (THM) model for frost heaving by integrating the most recent advances in unsaturated soil mechanics. The advantage of this proposed model over earlier models stems from a formulation consistent with continuum mechanics for both saturated and unsaturated soils under both frozen and unfrozen conditions. All the material properties have been defined in the existing unsaturated soil mechanics and can be easily measured. In addition, the model can be easily generalized into arbitrary 1D, 2D, and 3D processes, and use the standard numerical techniques in solving boundary value problems. Simplicity and effectiveness of the model has been demonstrated by implementing the proposed model into a commercially available software COMSOL with some example under typical laboratory and field conditions. Three demonstration cases are provided. In the first case, soil behaviors in the unfrozen state are simulated, which is Biot's consolidation. Mandel-Cryer effect is used to validate the correctness of the programmed model. In the second and third cases, frost heaving in open- and closed water supply systems are simulated. In both cases, the decrease of temperature leads to part of the in-situ water frozen to ice, which induces the suction force in the freezing area. The suction force drives the water in unfrozen zone flow to the freezing front. When the migrated water is frozen, it induces higher ice content in the freezing zone and ice lenses are formed. With the accumulation of ice in the freezing zone, the hydraulic conductivity decreases, in which process the flow-in rate of moisture decreases as well. For a closed system, one special phenomenon is that the soil shrinkage of the warmer part due to the moisture transfer can also be simulated. After that, the new model is validated using the frost heave data in existing literatures. Two freezing types are considered, which are step freezing and ramped freezing as shown in Fig. 1. For step freezing, the temperatures at the warm and cold plates do not change during the freezing process. For ramped freezing, the temperatures at the warm and cold plates decreased at a certain rate. Fig. 2 shows that comparisons between measured and simulated results on heaving magnitudes and frost fringes during step and ramped freezing. The left image in Fig. 2 is the result of step freezing. At the beginning, the heaving magnitude quickly increased and frost fringe quickly moved downward. With an increase in the freezing time, the heaving rates and magnitudes as well as the location of frost fringe stabilized. The heaving and frost fringe exhibited different modes for ramped freezing. The heaving magnitude increased slowly at the beginning, and became more and more quickly until stabilized with time. The frost fringe moved evenly with the increasing of freezing time. Fig. 2. Comparisons between Measured and Simulated Results on Frost Heave during Step and Ramped freezing Overall, the new model can simulate the physical process of frost heaving and many features in frost heaving, such as generation of negative pore water pressure, heaving, ice formation, shrinkage of unsaturated soil under limited water access, and soil consolidation. The validations indicate that the proposed model can reasonably simulate the heaving magnitudes and the location of frost fringes as well.
J. Yin and X. Zhang, "A Coupled Thermal-Hydraulic-Mechanical Model for Frost Heave," Proceedings of the 7th Asia-Pacific Conference on Unsaturated Soils (2019, Nagoya, Japan), Japanese Geotechnical Society, Aug 2019.
7th Asia-Pacific Conference on Unsaturated Soils, AP-UNSAT 2019 (2019: Aug. 23-25, Nagoya, Japan)
Civil, Architectural and Environmental Engineering
Keywords and Phrases
Coupled thermal-hydraulic-mechanical; Engineering prediction; FEM; Frost heaving; Soil freezing; Suction; Unsaturated soil mechanics
Article - Conference proceedings
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25 Aug 2019