Abstract
This research work presents an experimental and numerical study of the coupled thermo-hydro-mechanical (THM) processes that occur during soil freezing. With focusing on the artificial ground freezing (AGF) technology, a new testing device is built, which considers a variety of AGF-related boundary conditions and different freezing directions. In the conducted experiments, a distinction is made between two thermal states: (1) The thermal transient state, which is associated with ice penetration, small deformations, and insignificant water suction. (2) The thermal (quasi-) steady state, which has a much longer duration and is associated with significant ice lens formation due to water suction. In the numerical modeling, a special focus is laid on the processes that occur during the thermal transient state. Besides, a demonstration of the micro-cryo-suction mechanism and its realization in the continuum model through a phenomenological retention-curve-like formulation is presented. This allows modeling the ice lens formation and the stiffness degradation observed in the experiments. Assuming a fully saturated soil as a biphasic porous material, a phase-change THM approach is applied in the numerical modeling. The governing equations are based on the continuum mechanical theory of porous media (TPM) extended by the phase-field modeling (PFM) approach. The model proceeds from a small-strain assumption, whereas the pore fluid can be found in liquid water or solid ice state with a unified kinematics treatment of both states. Comparisons with the experimental data demonstrate the ability and usefulness of the considered model in describing the freezing of saturated soils.
Highlights
The need for efficient, environmentally friendly and modern infrastructures, especially in big cities with a high population density, has led to an increase in the dependency on underground constructions such as underground traffic routes
A special focus is laid on the processes that occur during the thermal transient state
The governing equations are based on the continuum mechanical theory of porous media (TPM) extended by the phase-field modeling (PFM) approach
Summary
The need for efficient, environmentally friendly and modern infrastructures, especially in big cities with a high population density, has led to an increase in the dependency on underground constructions such as underground traffic routes. The major objective of this work is to gain new insight into the challenging coupled thermo-hydromechanical processes that occur during soil freezing via applying an advanced experimental and numerical study This is achieved by (1) building a new multi-directional soil freezing testing device that allows the application of different mechanical and thermal boundary conditions, (2) measuring the time-dependent thermo-hydro-mechanical changes in the domain and at the boundaries of the specimens, (3) implementation and validation of a simplified unified water/ice kinematics porous media approach to model the coupled phase-change thermo-hydro-mechanical processes, and (4) extending the modeling framework via a retention-curve-like formulation to consider the microcryo-suction mechanism and, allowing to capture the deformations in the transient and the (quasi-) steady state due to ice lens formation.
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