1 Analytical study of freezing behavior of a cavity in thermo‐poro‐elastic medium H.T. Nguyen 1,2 , H.Wong 1 , A.Fabbri 1 , J.F. Georgin 2 , E. Prudhomme 2 1. Université de Lyon/ENTPE/LTDS (UMR CNRS 5513), 69120 Vaulx‐en‐Velin, France 2. Université de Lyon/INSA, 69621 Villeurbanne Cedex, France Abstract The goal of this paper is to present an analytical solution to have a first insight of the impact of ice formation on the surrounding porous rock on underground cavities like reservoir, pipes, tunnels or wellbores. Among the other analytical solutions found in the literature on this topic, the originality of this work resides in the rigorous theoretical framework of poromechanics, which considers the coupling between liquid water and ice crystal under thermodynamic equilibrium. Liquid water transport, thermal conduction, and elastic properties of the phases are also considered. Two analytical solutions are presented, based on a linearization of the system of governing equations. The first one deals with a spherical cavity within an infinite porous medium leading to an exact analytical solution. It allows validating the Stehfest’s algorithm on the numerical inversion of Laplace Transform, used in the second analytical solution, which considers a cylindrical excavation. The validity of this solution is assessed by comparing its results to that issued from a numerical resolution of the nonlinear system of equations. The analytical solution is then ultimately used to identify the influence of key parameters like the thermal/hydraulic conductivities, the amount of ice formed and the thermal dilatation coefficients on the mechanical response of a cylindrical cavity submitted to an internal frost. Keywords: Cold region underground structure, freezing‐thawing of porous continua, stress and displacement fields, analytical poro‐elastic solutions 1. Introduction Damage induced by frost action upon civil engineering structures is a source of main concern in cold climates [1]. If we consider underground structures, sub‐zero cooling can come from the surrounding rock mass (for example tunnel and pipeline in permafrost or seasonally frozen soils [2], [3]), or from the core of the structure (for example tunnel in cold climate within a temperature buffered rock mass [4] or leaking CO2 well submitted to Joule‐Thomson cooling [5]). Whatever the case, the structure and the surrounding rock mass are under strong thermal gradient and their behavior is governed by complex coupled processes. Theoretical studies of geomaterials behavior at low temperature started with the work of Powers in 1949 [6] [7], which attributed the expansion of concrete to the hydraulic pressure originated by the expulsion of liquid water from the freezing pores due to the liquid‐to‐ice volumetric expansion. However, the picture was not as simple as demonstrated by the fact that expansion is also observed in cement paste saturated with benzene, whose density increases with solidification [8].