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This paper investigates the thermo-hydro-mechanical (THM) behaviour of soils subjected to seasonal temperature variations in both permafrost and seasonally frozen conditions. Numerical modelling of soil freezing and ice segregation processes is presented, and compared against small-scale physical modelling experiments. The coupled THM model presented, which is solved by way of a transient finite element approach, considers a number of processes, including conduction, convection, phase change, the movement of moisture due to cryogenic suctions, and the development of ice lenses. Two seasonal freezing scenarios are considered: (a) for soils with no permafrost, where freezing is from the surface downward (one-sided freezing); and (b) for soils underlain by permafrost, where large thermal gradients in the uppermost permafrost layer can cause active layer freezing in two directions, from the permafrost table upwards and from the ground surface downwards (two-sided freezing). In the case of one-sided freezing, ice lens formation occurs as the freezing front advances downwards from the surface, and is limited by water supply. However, during two-sided freezing, ice segregation takes place in a closed system, with ice lenses accumulating at the base of the active layer and near the ground surface, leaving an intervening ice-poor zone. Numerical modelling is able to represent the development of both the thermal field and ice segregation observed in the physical models. The significance of this contrasting ground ice distribution is considered in the context of thaw-related slow mass movement processes (solifluction).

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This paper presents a formulation for coupled heat and moisture transfer in a deformable partially saturated soil. The research is based on a mechanistic phase interaction model coupled to a state surface approach. The method takes into account the coupling effect of temperature gradient and deformations on flows in porous media. Pore water pressure, pore air pressure, temperature and displacement are treated as the primary unknowns. A numerical solution of the formulation is then achieved via the finite element method. An example of the use of the new model is then presented.

Along with horizontal drilling techniques, multi-stage hydraulic fracturing has improved shale gas production significantly in past decades. In order to understand the mechanism of hydraulic fracturing and improve treatment designs, it is critical to conduct modelling to predict stimulated fractures. In this paper, related physical processes in hydraulic fracturing are firstly discussed and their effects on hydraulic fracturing processes are analysed. Then historical and state of the art numerical models for hydraulic fracturing are reviewed, to highlight the pros and cons of different numerical methods. Next, commercially available software for hydraulic fracturing design are discussed and key features are summarised. Finally, we draw conclusions from the previous discussions in relation to physics, method and applications and provide recommendations for further research.