Numerical simulation of soil stability during artificial freezing

Abstract

Artificial ground freezing is an efficient method for construction of vertical mine shafts under hard geological and hydrological conditions. The present article is devoted to a numerical simulation of mechanical behavior of soils surrounding freezing wells during a shaft sinking with a use of the artificial ground freezing method. The numerical simulation is carried out on the basis of a thermo-hydro-mechanical model of freezing process in a water saturated rock mass. Constitutive relations are derived within framework of thermo-poromechanics in consideration of the phase transition. Description of the mechanical behavior of soils is performed in the elasto-plastic formulation. The model allows one to take into consideration an influence of frost heave and temperature change on strain of soils under freezing process. Plastic strain is estimated with a use Drucker-Prager criterion. The numerical simulation of artificial freezing of a rock mass has been carried out for two cases. In the first case a response of soils adjacent to freezing wells on an application of the AGF method and a shaft sinking has been analyzed. In the second case stress-strain state in a neighborhood of the freezing well has been determined. It has been shown that the artificial freezing and excavation works leads to an increase of mechanical pressure in near-wellbore domains. Frost heave and temperature deformation induced by the artificial freezing cause displacement of soil in the vertical and horizontal directions.